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## **Meet the editor**

Dr. Ahmet Mesrur Halefoğlu is currently working as a resident specialist of Radiology and an associate professor at Sisli Etfal Training and Research Hospital, Istanbul, Turkey. He has completed Antakya High School at Antakya, Hatay, Turkey, with honors degree and has graduated from Istanbul University Cerrahpaşa Faculty of Medicine in 1986, Istanbul, Turkey. He completed his res-

idency between 1992 and 1997 at Sisli Etfal Training and Research Hospital, Istanbul, Turkey. He has served as postdoctoral research fellowship at Johns Hopkins Hospital, Baltimore, MD, USA, between 1998 and 1999. He has also been a research observer at Johns Hopkins Hospital in the years 2002 and 2004. He is mostly dealing with research fields in body imaging and neuroradiology with multidetector computed tomography and high-resolution magnetic resonance imaging. He has more than 50 high impact factor publications and has written 3 book chapters. He is a member of the Turkish Society of Radiology and European Society of Radiology.

## Contents



Chapter 8 **Usefulness of Cone Beam Computed Tomography for the Diagnosis and Treatment of Oral and Maxillofacial Pathology 169** Márcio Diniz-Freitas, Javier Fernández-Feijoo, Lucía García-

Caballero, Maite Abeleira, Mercedes Outumuro, Jacobo Limeres-Pose and Pedro Diz-Dios

	- **Section 3 Life Sciences 249**

## Preface

Chapter 8 **Usefulness of Cone Beam Computed Tomography for the Diagnosis and Treatment of Oral and Maxillofacial**

**Section 2 Physical Sciences, Engineering and Technology 187**

Chapter 10 **The Use of Computed Tomography to Explore the**

Chapter 9 **Novelty Detection‐Based Internal Fingerprint Segmentation in Optical Coherence Tomography Images 189**

Miguel A. Vicente, Jesús Mínguez and Dorys C. González

Chapter 11 **Physical Transport Properties of Porous Rock with Computed**

Chapter 13 **Computed Tomography in Veterinary Medicine: Currently Published and Tomorrow's Vision 271**

Rethabile Khutlang, Pheeha Machaka, Ann Singh and Fulufhelo

**Microstructure of Materials in Civil Engineering: From Rocks to**

Matthew Keane, Emily Paul, Craig J Sturrock, Cyril Rauch and Catrin

Márcio Diniz-Freitas, Javier Fernández-Feijoo, Lucía García-Caballero, Maite Abeleira, Mercedes Outumuro, Jacobo Limeres-

**Pathology 169**

**VI** Contents

Nelwamondo

**Concrete 207**

**Tomography 231**

**Section 3 Life Sciences 249**

Sian Rutland

Wenzheng Yue and Yong Wang

Chapter 12 **Vascular and Cardiac CT in Small Animals 251** Giovanna Bertolini and Luca Angeloni

Pose and Pedro Diz-Dios

It is my honor to introduce the book entitled *Computed Tomography – Advanced Applications*. Computed tomography (CT) has become an invaluable imaging modality in clinical medi‐ cine, but it also has many different application areas including veterinary medicine, dentist‐ ry, and engineering.

The term *tomography* comes from the Greek words *tomos* (a cut, a slice, or a section) and *gra‐ phein* (to write or record).

Computed tomography (CT) is a noninvasive cross-sectional imaging modality based on the absorption of X-rays in objects. It consists of a matrix of attenuation values depicted in vari‐ ous shades of gray, thereby creating a spatial image of the scanned object. In medicine, even though it is possible to obtain images of the inner human body, one can also hamper super‐ imposition of the different anatomical structures.

Nowadays, CT systems have spiral or helical scanning technology. In addition, many CT systems are capable of imaging multiple slices simultaneously. Helical CT has several ad‐ vantages over older CT techniques: it is faster, produces better three-dimensional (3D) pic‐ tures of areas inside the body, and may detect small abnormalities better. The newest CT scanners, called multislice CT or multidetector CT scanners, allow more slices to be imaged in a shorter period of time.

The advent and rapid diffusion of advanced multidetector-row scanner technology offers comprehensive evaluation of different anatomic structures in daily practice. Multidetector CT scanners have the capability of obtaining high-quality three- dimensional (3D) mapping of the vascular system called CT angiography. Dual-source CT technology is also now avail‐ able and plays an important role in the tissue analysis and characterization.

The aim of this book is to introduce the applications of CT imaging not only in general med‐ icine but also in different fields especially in veterinary medicine, dentistry, and engineer‐ ing. Recent developments in CT technology have led to a widening of its applications on many areas like material testing in engineering, 3D evaluation of teeth, and the vascular and cardiac evaluations of small animals.

> **Ahmet Mesrur Halefoğlu, MD** Department of Radiology, Sisli Hamidiye Etfal Training and Research Hospital, Istanbul, Turkey

**Section 1**

**Health Sciences**

## **Advances in Cardiac Computed Tomography**

Karthik Ananthasubramaniam, Nishtha Sareen and Gjeka Rudin

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68554

#### **Abstract**

Coronary cardiac computed tomography (CCTA) has seen rapid improvements in technology including hardware and postprocessing techniques that have contributed to its rapid growth and enabled it to remain in the forefront on diagnostic imaging. Important technological advances include wider detectors for greater coverage with less gantry rotation times, dual-source computed tomography (CT) with improved temporal resolution, dual-energy CT where simultaneous imaging at different energies to increase the contrast difference between different tissues enhances diagnostic accuracy, and emergence of spectral CT to enhance atherosclerotic imaging through nanoparticle technology. Software advances include iterative reconstruction methodologies to reduce noise and radiation doses, plaque imaging and quantification tools to assess plaque morphology and stenosis severity. Processing advances using computational fluid dynamics now enables the determination of fractional flow reserve (FFR). Another important advancement in CCTA physiologic imaging is CCTA perfusion imaging to detect ischemia and compares favorably with myocardial perfusion imaging and coronary angiographic stenosis. Finally, large registry studies and single-center studies have now been published assessing the incremental value of coronary calcium score, CT plaque severity of disease and have demonstrated that the CCTA carries strong prognostic value over and above traditional risk assessment in predicting adverse outcomes.

**Keywords:** coronary computed tomography angiography, CT advances, CT perfusion imaging, CT fractional flow reserve, prognosis

### **1. Introduction**

Cardiac computed tomography (CT), specifically coronary CT angiography (CCTA), has made major progress and currently is one of the leading noninvasive modalities for diagnosis of coronary artery disease (CAD) during the past years. The progress can be attributed to many

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

reasons but chief among them are progressive establishment of CCTA as a front-line imaging modality for diagnosis and prognosis of coronary artery disease. This was shown by randomized trials and multicenter registry-based evidence totaling tens of thousands of patients. The second important factor contributing to the rapid rise of CT is advancements in CT technology in hardware and new software solutions, such as refined image reconstruction methods. Due to such advances, CCTA has enjoyed progressive enhancements in image quality and achieved better temporal and spatial resolution. Most importantly, CCTA is now possible with much lower radiation doses than a traditional SPECT scan. Furthermore, with some advanced scanners and scanning methodologies current doses approach the 1-milliseivert range which is a mind-boggling advance since the inception of the technique not too long ago in early 2000.

### **2. Historical perspective**

The first CCTA was performed using electron-beam CT in the 1990s [1]. X-ray beams were produced by an electron beam, and were directed toward stationary targets around the patient. This image was produced at a temporal resolution of 100 ms but was insufficient to image coronaries given a slice thickness of 1.5–3 mm. However, this laid the groundwork for manufacturers to move the field forward with the multislice CST (MSCT), and the first four-slice CT in 2000 for coronary visualization had a gantry rotation time of 500 ms and a temporal resolution of 250 ms [2]. Subsequently, this evolved into 16-, 40-, and then 64-slice CT. There was slight improvement in slice thickness but now with an ability to image the heart in 4–8 heart beats. This led to reduction in less breath hold times, lesser artifacts, higher speed of contrast use, and thus lesser contrast volume. Multiple studies have now established the diagnostic accuracy of 64-slice CCTA using retrospective helical acquisition techniques [3, 4].

### **3. Equipment advances in CCTA**

Although 64-slice CCTA remains the workhorse of coronary imaging, manufacturers have worked continuously to move technology forward. While some have just increased the number of slices in detectors which then translates to greater scan coverage and thus acquisition of the image needed in shorter number of heart beats, others have used dual-scanner technology (dual-source CT at 90° angle) to enable increasing temporal resolution by a factor of 2.

1. **Wide detector CT:** By increasing the number of CT scanner detector width (number of slices), a great amount of coverage of the heart in a single gantry rotation can be achieved. Each detector row has a width (collimation) of 0.5–0.6 mm. So, a 64-slice detector can cover 64 × 0.5 = about 38 mm of scan coverage. Thus, a wider detector array such as 320-detector CT would provide a single gantry rotation coverage of 320 × 0.5 = 160 mm. Since the approximate coverage to scan the entire heart is about 120 mm, a 65-slice scanner would need about 4 gantry rotations, and a 320-slice scanner could cover the entire heart in one rotation. The disadvantage of wide detector CT is that due to extra rotation at the beginning and end of scan to avoid cone beam reconstruction artifact (over ranging), there is extra radiation burden to patient and also additionally areas not in the field of interest also being exposed to radiation. **Table 1** provides a comparison of CT scan characteristics and acquisition parameters over a wide range of detector widths, and **Figure 1** provides a comparative illustration of detector coverage depending on the number of detector rows in MSCT.

reasons but chief among them are progressive establishment of CCTA as a front-line imaging modality for diagnosis and prognosis of coronary artery disease. This was shown by randomized trials and multicenter registry-based evidence totaling tens of thousands of patients. The second important factor contributing to the rapid rise of CT is advancements in CT technology in hardware and new software solutions, such as refined image reconstruction methods. Due to such advances, CCTA has enjoyed progressive enhancements in image quality and achieved better temporal and spatial resolution. Most importantly, CCTA is now possible with much lower radiation doses than a traditional SPECT scan. Furthermore, with some advanced scanners and scanning methodologies current doses approach the 1-milliseivert range which is a mind-boggling advance since the inception of the technique not too long ago in early 2000.

The first CCTA was performed using electron-beam CT in the 1990s [1]. X-ray beams were produced by an electron beam, and were directed toward stationary targets around the patient. This image was produced at a temporal resolution of 100 ms but was insufficient to image coronaries given a slice thickness of 1.5–3 mm. However, this laid the groundwork for manufacturers to move the field forward with the multislice CST (MSCT), and the first four-slice CT in 2000 for coronary visualization had a gantry rotation time of 500 ms and a temporal resolution of 250 ms [2]. Subsequently, this evolved into 16-, 40-, and then 64-slice CT. There was slight improvement in slice thickness but now with an ability to image the heart in 4–8 heart beats. This led to reduction in less breath hold times, lesser artifacts, higher speed of contrast use, and thus lesser contrast volume. Multiple studies have now established the diagnostic accuracy of 64-slice CCTA

Although 64-slice CCTA remains the workhorse of coronary imaging, manufacturers have worked continuously to move technology forward. While some have just increased the number of slices in detectors which then translates to greater scan coverage and thus acquisition of the image needed in shorter number of heart beats, others have used dual-scanner technology

1. **Wide detector CT:** By increasing the number of CT scanner detector width (number of slices), a great amount of coverage of the heart in a single gantry rotation can be achieved. Each detector row has a width (collimation) of 0.5–0.6 mm. So, a 64-slice detector can cover 64 × 0.5 = about 38 mm of scan coverage. Thus, a wider detector array such as 320-detector CT would provide a single gantry rotation coverage of 320 × 0.5 = 160 mm. Since the approximate coverage to scan the entire heart is about 120 mm, a 65-slice scanner would need about 4 gantry rotations, and a 320-slice scanner could cover the entire heart in one rotation. The disadvantage of wide detector CT is that due to extra rotation at the beginning and end of scan to avoid cone beam reconstruction artifact (over ranging), there is extra radiation burden to patient and also additionally areas not in the field of interest also being exposed

(dual-source CT at 90° angle) to enable increasing temporal resolution by a factor of 2.

**2. Historical perspective**

4 Computed Tomography - Advanced Applications

using retrospective helical acquisition techniques [3, 4].

**3. Equipment advances in CCTA**



\* Double *z-*sampling. ‡ Temporal resolution can be improved to 83 ms with dual source acquisitions in single-energy applications. § Temporal resolution can be improved to 58 ms with multisegment acquisition and multisegment reconstruction

Abbreviation: MDCT, multidetector CT

Schuleri K.H. *et al. Nat. Rev. Cardiol*. **6**, 699–710 (2009); doi:10.1038/nrcardio.2009.172

**Table 1.** Technical and acquisition parameters for cardiac examinations with MDCT.

**Figure 1.** Technical progression of scanner technology. Improvement in coverage of the *z*-axis with 4-, 16-, and 64-slice detector rows, relative to wide-range 320-slice detector rows. With the wide-range technology, the entire heart is covered in one gantry rotation. Schuleri, K. H. *et al. Nat. Rev. Cardiol*. **6**, 699–710 (2009); doi:10.1038/nrcardio.2009.172.

of the entire heart and deliver extremely high spatial resolution capable of imaging distal small coronary arteries, much better stented lumen delineation, and less artifacts from calcium. The major limitations currently are poor temporal resolution (2 s) and poor contrast resolution (5–10 Hounsfield units compared to 1 Hounsfield unit for MSCT) [14]. Currently as most evidence is limited to preclinical and animal studies, further research and studies are needed in this field.

**Figure 2.** (A) Coronary CT with 320-slice CT. (B) Coronary CT with high-pitch prospective scanning. Achenbach S et al. Cardiol Clin 30 (2012) 1–8.


**Table 2.** Current applications of dual-energy and spectral CT techniques.

### **4. Advances in temporal and spatial resolution**

of the entire heart and deliver extremely high spatial resolution capable of imaging distal small coronary arteries, much better stented lumen delineation, and less artifacts from calcium. The major limitations currently are poor temporal resolution (2 s) and poor contrast resolution (5–10 Hounsfield units compared to 1 Hounsfield unit for MSCT) [14]. Currently as most evidence is limited to preclinical and animal studies, further research and

**Figure 1.** Technical progression of scanner technology. Improvement in coverage of the *z*-axis with 4-, 16-, and 64-slice detector rows, relative to wide-range 320-slice detector rows. With the wide-range technology, the entire heart is covered

in one gantry rotation. Schuleri, K. H. *et al. Nat. Rev. Cardiol*. **6**, 699–710 (2009); doi:10.1038/nrcardio.2009.172.

**Number of detector slices 4 16 64 256 320**

Slice width (mm) 1.3 0.8–1.0 0.5–0.8 0.6 0.5 Spatial resolution (mm) 1 0.6 0.4–0.6 0.4 0.35 Rotation time (s) 0.5 0.375–0.420 0.33–0.40 0.27 0.35 Temporal resolution (ms) 250 188–210 165–200‡ 135 175§ *z*-axis coverage (mm) 4–5 8–12 32–40 80 160

Schuleri K.H. *et al. Nat. Rev. Cardiol*. **6**, 699–710 (2009); doi:10.1038/nrcardio.2009.172

**Table 1.** Technical and acquisition parameters for cardiac examinations with MDCT.

64 × 0.5 64 × 0.65 2 × 32 × 0.6\*

40 15–20 6–12 1–2 >1

Temporal resolution can be improved to 58 ms with multisegment acquisition and multisegment

Temporal resolution can be improved to 83 ms with dual source acquisitions in single-energy

2 × 128 × 0.625\*

320 × 0.5

16 × 0.5 16 × 0.625 16 × 0.75

Detector collimation

Scan time to cover the entire heart volume (s)

\* Double *z-*sampling. ‡

Abbreviation: MDCT, multidetector CT

applications. §

reconstruction

4 × 1 4 × 1.25

6 Computed Tomography - Advanced Applications

(mm)

studies are needed in this field.

Continuing advances are being made in the development of faster scanners and in the pipeline is GE.

Revolution CT TM (GE Healthcare, Milwaukee, WI) with a wider *z*-axis coverage and a gantry rotation time of 0.2 s providing wider *z*-axis coverage and single beat image acquisition (Revolution CT 2014; available at www.gehealthcare) and the Seimens Somatom Force TM (Seimens AG, Erlangen, Germany) providing very high temporal resolution of 66 ms and spatial resolution of 0.24 s and able to image the heart in a single beat with Turbo Flash mode with the need for breath hold. These superb technological advances need formal clinical validation (Somatom Force TM available at www.seimens.com).

Typical MSCT detectors have solid-state ceramic detectors which help to convert X-rays to visible light followed by conversion to analog electrical signal which then gets converted to a digital signal for image formation. The detectors all have septate electric boards which are all then linked to each other.

However, with breakthrough in technology one vendor has introduced a new detector system called Stellar Detector (Stellar Detector TM, Seimens AG, Erlangen, Germany) which combines all detectors into single electric board and claims superior spatial resolution and decrease in image noise.

GE has introduced Gemstone Detector which is a garnet-based substance which has much shorter decay and after-glow times enabling much rapid processing of signal improving spatial resolution and decreasing image noise. This concept has proven useful in reading CTAs in stent, determining intrastent diameter and area due to decrease in image noise [15]. It appears to be compatible with dual-energy scanners too.

### **5. Software advances in CCTA**


(Seimens AG, Erlangen, Germany) providing very high temporal resolution of 66 ms and spatial resolution of 0.24 s and able to image the heart in a single beat with Turbo Flash mode with the need for breath hold. These superb technological advances need formal clinical vali-

Typical MSCT detectors have solid-state ceramic detectors which help to convert X-rays to visible light followed by conversion to analog electrical signal which then gets converted to a digital signal for image formation. The detectors all have septate electric boards which are all

However, with breakthrough in technology one vendor has introduced a new detector system called Stellar Detector (Stellar Detector TM, Seimens AG, Erlangen, Germany) which combines all detectors into single electric board and claims superior spatial resolution and

GE has introduced Gemstone Detector which is a garnet-based substance which has much shorter decay and after-glow times enabling much rapid processing of signal improving spatial resolution and decreasing image noise. This concept has proven useful in reading CTAs in stent, determining intrastent diameter and area due to decrease in image noise [15]. It appears

a. **Iterative reconstruction (IR):** Although filtered back-projection remains a common method of reconstruction, IR techniques are more commonly being used where image information is used to simulate expected image based on CT measurements and then these simulated data are modified in subsequent image reconstruction. This technique has been shown to reduce image noise and reduction in radiation doses [16, 17]. **Figure 3** shows an

b. **Motion correction:** Motion artifact is one of the most important limitations in CCTA affecting overall accuracy. Techniques such as heart rate control and faster scanning with wide detector and dual source technologies are ways to limit motion artifact. Recently, GE Healthcare has introduced Snapshot FreezeTM where the software evaluates multiple adjacent cardiac phases within the same cardiac cycle to evaluate and plot coronary artery motion and eliminate residual coronary motion artifact. This promises to further minimize motion artifact im-

c. **Arrhythmia detection:** Occurrence of arrhythmias causes significant issues with missing data and artifacts in CCTA. Advances in arrhythmia detection include using of complex arrhythmia detection algorithms to enable stopping the scan when arrhythmia occurs and restarting scans after arrhythmia subsides to enable capturing data in the right cardiac cycles (Seimens Healthcare, Forcheim, Germany). Other advances include image reconstruction using identical filling concepts isovolumetric phases (which contain best image data) are

dation (Somatom Force TM available at www.seimens.com).

to be compatible with dual-energy scanners too.

**5. Software advances in CCTA**

example of noise reduction with IR.

used in image reconstruction [19].

proving the image quality and interpretability [18].

then linked to each other.

8 Computed Tomography - Advanced Applications

decrease in image noise.

**Figure 3.** Image noise reduction with iterative reconstruction technology. Achenbach S et al. Cardiol Clin 30 (2012) 1–8.

d. **Radiation reduction:** Apart from prospective gating, traditional ECG tube current modulation, wide detector coverage, and dual source high-pitch-scanning techniques all of which dramatically reduce radiation; further advances are being done to do real-time modulation of attenuation-based adjustments in tube potential, thus driving radiation doses down even further (Care Dose4D TM; Seimens Healthcare, Forcheim, Germany).

### **6. Advances in CCTA beyond traditional noninvasive coronary angiography**

CCTA has been recognized as a cost-effective noninvasive diagnostic modality [20]. Evolving literature has established that revascularization has clinical benefit when performed in stenosis with hemodynamic significance [21, 22]. An intermediate stenosis on CT scan is not a good predictor of physiological significance [23–25]; this calls for additional tools which can provide complementary physiological data to available anatomy. Noninvasive fractional flow reserve (FFR) evaluation on CT, myocardial CT perfusion, and transluminal attenuation gradient (TAG) are the three techniques with clinical evidence. We will talk briefly about these in this section of the chapter.

### **6.1. Noninvasive fractional flow reserve evaluation on CCTA: physiology**

FFR is defined as the ratio of the mean coronary pressure distal to a coronary stenosis to the mean aortic pressure during maximal coronary blood flow. An FFR value of 0.80 or less suggests lesion-specific hemodynamic significance [26]. Incorporation of FFR in CT does not call for any modification of CCTA protocols, additional image acquisition, or administration of medications. The calculation is performed by segmentation of coronary tree and left ventricular mass and application of computational fluid dynamics (see **Figure 4**). While no adenosine administration is performed, the conditions to simulate the same can be established.

### *6.1.1. Clinical evidence*

FFR incorporation into routine CT has been compared to visual estimation alone in multiple studies. We now have evidence from an integrated analysis of data from three prospective, international, and multicenter trials, which assessed the diagnostic performance of FFR CT using invasive FFR as a reference standard [27]. The key trials outlining the value of CT FFR were the DISCOVER-FLOW, DeFACTO, and the NXT trials. These studies with cumulative over 600 patients concluded that with intermediate coronary stenosis, FFR CT remained both highly sensitive and specific with respect to the diagnosis of ischemia. Specifically, CT FFR had higher sensitivity than CT (81 vs. 53%) Additionally, when compared to invasive FFR evaluation, FFR CT had higher diagnostic accuracy (86 vs. 71%) in the identification of hemodynamically significant lesions.

More exciting data have suggested an economic benefit associated with a 12% reduction in adverse cardiovascular events at 1 year with the use of CT FFR when compared to angiography with stenosis-based PCI [28]. In their study, Hlatky et al. applied a decision analysis comparing five clinical strategies constructed as follows: (1) angiography with stenosis-based PCI; (2) angiography with FFR-guided PCI; (3) coronary CTA followed by angiography and

**Figure 4.** Simplified scheme of computational fluid dynamic techniques for simulating hyperemic flow and pressure applied to CTA data. Min JK. JCCT 2011;5(5);301-9.

stenosis-based PCI; (4) coronary CTA followed by angiography and FFR-guided PCI and (5) coronary CTA–FFR CT followed by FFR CT-guided PCI. The projected initial management costs were highest for angiography with stenosis-based PCI and lowest for the coronary CTA– FFR CT followed by FFR CT-guided PCI. Inspired from this concept, we now have a prospective, controlled utility trial evaluating patients with an intermediate likelihood of CAD PLATFORM (Prospective Longitudinal Trial of FFR CT: Outcome and Resource IMpacts) [29]. Patients referred for noninvasive evaluation formed the first cohort and those referred for invasive coronary angiogram comprised the second cohort. These were evaluated by using standard care approach (first phase) and coronary CTA with physiologic FFR evaluation (second stage). The primary result was that among those with intended ICA (FFRCT-guided = 193; usual care = 187), no-obstructive CAD was found at ICA in 24 (12%) in the CTA/FFRCT arm and 137 (73%) in the usual care arm (*P* < 0.0001), with similar mean cumulative radiation exposure (9.9 vs. 9.4 mSv, *P* = 0.20). Invasive coronary angiography was cancelled in 61% after receiving CTA/FFRCT results. Clinical event rates within 90 days were low in both the arms. This is just another example of how CT FFR is a feasible and safe alternative to invasive angiography and was associated with a significantly lower rate of invasive angiography showing no-obstructive CAD (**Figure 5a** and **b**).

We await the results of the multicentric registry ADVANCE (assessing diagnostic value of noninvasive FFRCT in coronary care) which will evaluate the clinical and economic impacts of FFR CT (NCT02499679).

#### *6.1.2. Clinical applications*

lesion-specific hemodynamic significance [26]. Incorporation of FFR in CT does not call for any modification of CCTA protocols, additional image acquisition, or administration of medications. The calculation is performed by segmentation of coronary tree and left ventricular mass and application of computational fluid dynamics (see **Figure 4**). While no adenosine

FFR incorporation into routine CT has been compared to visual estimation alone in multiple studies. We now have evidence from an integrated analysis of data from three prospective, international, and multicenter trials, which assessed the diagnostic performance of FFR CT using invasive FFR as a reference standard [27]. The key trials outlining the value of CT FFR were the DISCOVER-FLOW, DeFACTO, and the NXT trials. These studies with cumulative over 600 patients concluded that with intermediate coronary stenosis, FFR CT remained both highly sensitive and specific with respect to the diagnosis of ischemia. Specifically, CT FFR had higher sensitivity than CT (81 vs. 53%) Additionally, when compared to invasive FFR evaluation, FFR CT had higher diagnostic accuracy (86 vs. 71%) in the identification of hemo-

More exciting data have suggested an economic benefit associated with a 12% reduction in adverse cardiovascular events at 1 year with the use of CT FFR when compared to angiography with stenosis-based PCI [28]. In their study, Hlatky et al. applied a decision analysis comparing five clinical strategies constructed as follows: (1) angiography with stenosis-based PCI; (2) angiography with FFR-guided PCI; (3) coronary CTA followed by angiography and

**Figure 4.** Simplified scheme of computational fluid dynamic techniques for simulating hyperemic flow and pressure

administration is performed, the conditions to simulate the same can be established.

*6.1.1. Clinical evidence*

10 Computed Tomography - Advanced Applications

dynamically significant lesions.

applied to CTA data. Min JK. JCCT 2011;5(5);301-9.

Enhanced specificity and accuracy in the available data has established FFR incorporation to CT as a promising new dimension in noninvasive modalities. It may serve as a "gate-keeper" to escalation to invasive coronary angiography in suitable patient population. We await many more exciting studies to define the niche for its role in daily clinical practice.

#### *6.1.3. Limitations*


### **6.2. Myocardial CT perfusion (myocardial CTP)**

Myocardial CTP protocol is composed of a stress phase acquisition and a rest phase acquisition, as with nuclear myocardial perfusion imaging [30]. Iodinated contrast is administered in both the stress and rest acquisition (60–75 ml for each acquisition), for a total contrast dose of

**Figure 5.** (a) Examples of a no-obstructive CAD on CTA and corresponding normal CT FFR and correlative coronary angiographic FFR of patient from the DeFACTO study. (b) Example of patient with obstructive coronary disease in left anterior descending coronary artery on CTA and corresponding abnormal CT FFR and correlative coronary angiographic FFR from the DeFACTO study.

approximately 130–150 ml. The pharmacological stress agents include adenosine, dipyridamole or regadenosin. Although it has been shown in many studies that pharmacological and exercise stress testing have comparable diagnostic characteristics, exercise is the preferred method of stress in myocardial perfusion imaging when possible [31].

There are two ways in which to set up a stress and rest myocardial CTP protocol based on the order of scan acquisition, namely stress phase first followed by rest phase, or vice versa (as illustrated in **Figure 6**).

As expected, the main consideration is that the first scan will be a "clean" acquisition, and that the contrast used in the first acquisition can cross-contaminate the second acquisition if the interval between the scans is less than approximately 30 min. On the other hand, when doing a stress phase acquisition first, the detection of myocardial ischemia is optimized by not having contamination of contrast; however, the second scan can underestimate the presence of infarct in the myocardium if a short scan interval is used. This is so because the contrast from the stress scan would accumulate in an area of myocardial infarct due to the slow wash-out phenomenon, leading to persistent perfusion defect during rest imaging. Thus, possible underestimation of myocardial infarction specifically if the second scan is done within 10 min of the first one. A coronary CTA acquisition can be acquired simultaneously with the rest acquisition, and beta-blockers and sublingual nitroglycerin can be given to optimize the second scan (**Table 3**)

#### *6.2.1. Clinical evidence*

The smaller initial studies have been conducted at various institutions with differences in protocols and reference standards. The unifying conclusion is that perfusion defects on myocardial


**Figure 6.** Full CTP Protocol: The protocol includes patient preparation and post-examination checkup (including an optional delayed phase acquisition (shaded box). All steps are as listed in sequence. Heart rhythm and symptoms are monitored throughout the entire examination. (Adopted with permission from Ref [31]).


**Table 3.** Advantages and disadvantages of different CTP protocol sequences (adopted with permission [30]).

approximately 130–150 ml. The pharmacological stress agents include adenosine, dipyridamole or regadenosin. Although it has been shown in many studies that pharmacological and exercise stress testing have comparable diagnostic characteristics, exercise is the preferred method of

**Figure 5.** (a) Examples of a no-obstructive CAD on CTA and corresponding normal CT FFR and correlative coronary angiographic FFR of patient from the DeFACTO study. (b) Example of patient with obstructive coronary disease in left anterior descending coronary artery on CTA and corresponding abnormal CT FFR and correlative coronary angiographic

There are two ways in which to set up a stress and rest myocardial CTP protocol based on the order of scan acquisition, namely stress phase first followed by rest phase, or vice versa

As expected, the main consideration is that the first scan will be a "clean" acquisition, and that the contrast used in the first acquisition can cross-contaminate the second acquisition if the interval between the scans is less than approximately 30 min. On the other hand, when doing a stress phase acquisition first, the detection of myocardial ischemia is optimized by not having contamination of contrast; however, the second scan can underestimate the presence of infarct in the myocardium if a short scan interval is used. This is so because the contrast from the stress scan would accumulate in an area of myocardial infarct due to the slow wash-out phenomenon, leading to persistent perfusion defect during rest imaging. Thus, possible underestimation of myocardial infarction specifically if the second scan is done within 10 min of the first one. A coronary CTA acquisition can be acquired simultaneously with the rest acquisition, and beta-blockers and sublingual nitroglycerin can be given to optimize the second scan (**Table 3**)

The smaller initial studies have been conducted at various institutions with differences in protocols and reference standards. The unifying conclusion is that perfusion defects on myocardial

stress in myocardial perfusion imaging when possible [31].

(as illustrated in **Figure 6**).

FFR from the DeFACTO study.

12 Computed Tomography - Advanced Applications

*6.2.1. Clinical evidence*

CTP correlate well with those on SPECT and also in some studies with stenosis on quantitative coronary angiography. We briefly present some of these studies.

George et al. [32] used a 64-detector MDCT or a 256-detector MDCT for image acquisition with adenosine as the stress agent. The combined analysis of all patients (including both scanner types) in this study showed a per-vessel territory sensitivity, specificity, positivepredictive value (PPV), and negative-predictive value (NPV) of 75, 87, 60, and 93%, respectively, when compared with QCA and SPECT. Using the same stress agent, Blankstein et al. [33] acquired myocardial CTP images using a dual-source CT scanner, which has higher temporal resolution. They confirmed that myocardial CTP is equivalent to SPECT in detecting coronary artery stenosis by QCA, with comparative sensitivity and specificity to prior study. One interesting derivation from this study was similar radiation exposure with full myocardial CTP when compared to SPECT MPI. Rocha-Filho et al. [34] demonstrated that adding perfusion information obtained from stress myocardial CTP to coronary CTA improves all diagnostic characteristics of CTA alone, with most significant impact on specificity and PPV. The size and severity evaluation of perfusion defect at rest and stress have been shown to be concordant between myocardial CTP and SPECT [35]. This concordance has been further validated in the form of excellent validation by a five-point scale and a total perfusion deficit score [36]. Myocardial CTP has proven equivalent to SPECT in the detection of stenosis found on QCA (sensitivity and specificity: 88 and 79% for myocardial CTP and 69 and 71% for SPECT, *p* = NS) with dipyridamole on a 64-detector MDCT scanner [37].

An additional concept is the utilization of dynamic myocardial perfusion. Ho et al. [38] demonstrated that stress and rest dynamic perfusion imaging can detect myocardial perfusion defect with good diagnostic accuracy when compared with SPECT MPI (per-segment sensitivity, specificity, PPV, and NPV of 83, 78, 79, and 82%, respectively) and with QCA (per-segment sensitivity, specificity, PPV, and NPV of 95, 65, 78, and 79%, respectively) and allows for defining time-attenuation curves with the potential for quantification of myocardial blood flow. This comes at the price of a much higher radiation dose when compared to static imaging.

### *6.2.2. Limitations*


It cannot be emphasized enough that a careful review of multiple phases of the cardiac cycle is a robust method to differentiate a true perfusion defect from an artifact.

#### In summary,


### **7. Transluminal attenuation gradient**

TAG is a modality that is based upon the kinetics of iodinated contrast media within coronary arteries. It is the linear regression coefficient between the lumen attenuation and axial distance along the vessel from the ostium. This method is based upon the contrast attenuation difference across a stenosis which may predict functional significance [40].

### **7.1. Clinical evidence**

stress have been shown to be concordant between myocardial CTP and SPECT [35]. This concordance has been further validated in the form of excellent validation by a five-point scale and a total perfusion deficit score [36]. Myocardial CTP has proven equivalent to SPECT in the detection of stenosis found on QCA (sensitivity and specificity: 88 and 79% for myocardial CTP and 69 and 71% for SPECT, *p* = NS) with dipyridamole on a 64-detector

An additional concept is the utilization of dynamic myocardial perfusion. Ho et al. [38] demonstrated that stress and rest dynamic perfusion imaging can detect myocardial perfusion defect with good diagnostic accuracy when compared with SPECT MPI (per-segment sensitivity, specificity, PPV, and NPV of 83, 78, 79, and 82%, respectively) and with QCA (per-segment sensitivity, specificity, PPV, and NPV of 95, 65, 78, and 79%, respectively) and allows for defining time-attenuation curves with the potential for quantification of myocardial blood flow. This comes at the price of a much higher radiation dose when compared to static imaging.

1. CT-related artifacts should be recognized in an attempt to minimize them. One major culprit is beam hardening, which is a phenomenon that occurs when X-ray beams pass through objects of high density, leading to a selective attenuation of lower-energy beams and increased mean energy of the remaining beams. The resulting appearance is a hypoenhanced region that may mimic areas of true perfusion defect. Such hypoenhanced region is usually triangular and appears to originate from the region of high attenuation next to it, and does not conform to vascular territories [39]. A particularly common location includes the basal inferolateral wall, due to proximity to the descending aorta with iodinated contrast and dense vertebral bodies. Attempts to develop an algorithm to minimize

beam-hardening artifacts are ongoing, with the use of iterative reconstruction.

temporal resolution of CT has led to marked decrease in this artifact.

is a robust method to differentiate a true perfusion defect from an artifact.

2. Myocardial CTP is also prone to motion artifacts similar to coronary CTA, particularly during the stress phase acquisition, due to the increased heart rate. Cardiac motion during the acquisition leads to hypoenhanced areas that can mimic true perfusion defects. Enhanced

It cannot be emphasized enough that a careful review of multiple phases of the cardiac cycle

• Myocardial CTP has the potential to become a robust clinical tool for the evaluation of chest

• The available literature is in a very preliminary stage with only single-center preliminary experiences. These are flawed by referral bias and absence of any standardized protocol.

• More research is needed in order to further define, optimize, and validate the modality.

MDCT scanner [37].

14 Computed Tomography - Advanced Applications

*6.2.2. Limitations*

In summary,

pain patients.

Changes in coronary opacification across a stenosis were found to predict abnormal resting coronary blood flow in a study by Chow et al. [41]. The comparison of coronary opacification after normalization to aorta was performed to severity of stenosis and thrombolysis in myocardial infarction flow in the coronary arteries at invasive coronary angiography. TAG significantly improves both sensitivity and specificity over CCTA stenosis degree alone [40].

### **7.2. Clinical applications**

The addition of TAG to CCTA may supplement detection of hemodynamic significance of coronary stenosis especially in severely calcified lesions. An advantage of TAG over FFR supplementation of CT is that there is no complex computation required [42].

### **7.3. Limitations**

The evidence on the role of TAG in CCTA is limited. Further validation of both diagnostic and prognostic role of this approach is required in larger studies.

### **8. Take home points**

The single most attractive characteristic of the summarized techniques is that they provide both anatomical and functional assessments of CAD. The current studies have demonstrated that these methods are feasible for noninvasive assessment of CAD and have the potential to provide incremental value in detecting functionally significant coronary stenosis over CCTA alone. The available data are preliminary, but definitely promising. This calls for dedicated research to identify the prognostic value and clinical outcomes of decision making based on these techniques.

### **9. CCTA and prognosis**

In an era where coronary artery disease (CAD) is the leading cause of death worldwide, noninvasive cardiac imaging is essential for the diagnosis and prognosis of patient with suspected or known coronary artery disease. While nuclear positron emission tomography (PET), SPECT, cardiac magnetic resonance imaging, and stress echocardiography are well-established modality with excellent diagnostic accuracy, coronary computed tomographic angiography (CCTA) has emerged in the past couple of decades and is rapidly growing as noninvasive testing modality for the detection of coronary artery disease (CAD). CCTA provides excellent anatomic information that is comparable with invasive coronary angiography and in addition can provide significantly more information about subclinical atherosclerosis [43–46].

This has attracted particular interest to explore prognostic implication of the CCTA in cardiology field. Several single- and multiple-center studies, including meta-analysis of large registry, have been done to evaluate its prognostic value and compare it to the traditional risk factors [47].

### **9.1. Clinical evidence**

Prognostic value of the CCTA was studied in a variety of patient population including symptomatic and asymptomatic subset of patients. Hadamitzky et al. analyzed large patient population of 17,793 from the international CONFIRM registry in patient with suspected coronary artery disease. Combining the CCTA data and the clinical risk scores, a modeled score was developed with end-point assessment being all-cause mortality at 2-year follow-up. The optimized score developed improved risk stratification and overall risk prediction beyond the clinical risk scores. Incremental prognostic value was noted particularly with plaque burden and vessel stenosis, with a proportional correlation for proximal segment involvement [48]. Similar outcome was replicated at longer 5-year follow-up studies [49].

Other studies evaluated the prognostic value of the CCTA based on the plaque location and whether the atherosclerotic plaque is obstructive or not and the number of vessels involved. Cheruvu et al. analyzed the CCTA prognosis in asymptomatic patients without modifiable cardiovascular risk factors [50]. A total number of 1884 patients from 12 different centers were enrolled and followed up for approximately 5 years. Both obstructive and non-obstructive CADs were found to predict MACE with increased HR associated with higher degree of stenosis. MACE ranged from 5.6% in patients with no CAD to 36.28% in patients with obstructive CAD. **Figure 7** shows the obstructive severity on CTA and clinical implications. **Table 4** provides a summary of some of prognostic studies in CCTA.

The additive information of the CCTA on atherosclerotic plaque features offers the promise to provide a more comprehensive view on total plaque burden. In emergent data, atherosclerotic plaque characteristics have been associated with plaque vulnerability; hence, several observational and prospective studies are done to correlate their ability to predict future cardiovascular events [51–54]. Feuchtner et al. characterized CTA features associated with worse clinical outcomes. The evaluation of the CTA findings was based on lesion severity, plaque types (the spectrum from different degrees of calcified to non-calcified), and high-risk plaque criteria (low attenuation by HU, napkin-ring, spotty calcification, and remodeling index). The study concluded that the low attenuation plaque of <60 HU and napkin-ring sign were the most powerful predictors for MACE. Prognosis was established as excellent long term if CTA is negative but worsens with increasing non-calcifying plaque component [55]. Similar

cardiac magnetic resonance imaging, and stress echocardiography are well-established modality with excellent diagnostic accuracy, coronary computed tomographic angiography (CCTA) has emerged in the past couple of decades and is rapidly growing as noninvasive testing modality for the detection of coronary artery disease (CAD). CCTA provides excellent anatomic information that is comparable with invasive coronary angiography and in addition can

This has attracted particular interest to explore prognostic implication of the CCTA in cardiology field. Several single- and multiple-center studies, including meta-analysis of large registry, have been done to evaluate its prognostic value and compare it to the traditional risk

Prognostic value of the CCTA was studied in a variety of patient population including symptomatic and asymptomatic subset of patients. Hadamitzky et al. analyzed large patient population of 17,793 from the international CONFIRM registry in patient with suspected coronary artery disease. Combining the CCTA data and the clinical risk scores, a modeled score was developed with end-point assessment being all-cause mortality at 2-year follow-up. The optimized score developed improved risk stratification and overall risk prediction beyond the clinical risk scores. Incremental prognostic value was noted particularly with plaque burden and vessel stenosis, with a proportional correlation for proximal segment involvement

Other studies evaluated the prognostic value of the CCTA based on the plaque location and whether the atherosclerotic plaque is obstructive or not and the number of vessels involved. Cheruvu et al. analyzed the CCTA prognosis in asymptomatic patients without modifiable cardiovascular risk factors [50]. A total number of 1884 patients from 12 different centers were enrolled and followed up for approximately 5 years. Both obstructive and non-obstructive CADs were found to predict MACE with increased HR associated with higher degree of stenosis. MACE ranged from 5.6% in patients with no CAD to 36.28% in patients with obstructive CAD. **Figure 7** shows the obstructive severity on CTA and clinical implications. **Table 4**

The additive information of the CCTA on atherosclerotic plaque features offers the promise to provide a more comprehensive view on total plaque burden. In emergent data, atherosclerotic plaque characteristics have been associated with plaque vulnerability; hence, several observational and prospective studies are done to correlate their ability to predict future cardiovascular events [51–54]. Feuchtner et al. characterized CTA features associated with worse clinical outcomes. The evaluation of the CTA findings was based on lesion severity, plaque types (the spectrum from different degrees of calcified to non-calcified), and high-risk plaque criteria (low attenuation by HU, napkin-ring, spotty calcification, and remodeling index). The study concluded that the low attenuation plaque of <60 HU and napkin-ring sign were the most powerful predictors for MACE. Prognosis was established as excellent long term if CTA is negative but worsens with increasing non-calcifying plaque component [55]. Similar

provide significantly more information about subclinical atherosclerosis [43–46].

[48]. Similar outcome was replicated at longer 5-year follow-up studies [49].

provides a summary of some of prognostic studies in CCTA.

factors [47].

**9.1. Clinical evidence**

16 Computed Tomography - Advanced Applications

**Figure 7.** Coronary artery disease (CAD) severity identified by coronary CT angiography and recommended management. Patients with a normal coronary CT angiography can be safely reassured. Follow-up for preventive therapy is recommended for non-obstructive (<50%) CAD. For obstructive CAD (≥50% stenosis), further testing is recommended to guide management [55].

concept was entertained by Nadjiri et al., who performed a semi-quantitative analysis of all non-calcified plaques or partially calcified plaques to quantify the low attenuation plaque volume (LAPV), total non-calcified plaque volume, and remodeling index. All these plaque characteristics were associated with increased MACE independently from the clinical risk presentation. The strongest prognosis was associated with LAPV, which carried additional information beyond the calcium score and the conventional coronary CTA [56]. High-risk plaque and plaque progression were also found to be independent risk factors for predicting ACS [57, 58]. **Figures 8**–**10** demonstrate images of different histologic plaque types, their quantitative measurements, and plaque-specific-associated risk.

Considering the well-known correlation of the diabetes mellitus and CAD, particular attention was directed of the CCTA implication in diagnosing diabetic patients with subclinical CAD and assessing the prognostic value in this subset of patients. On prospective evaluation of 525 asymptomatic diabetic patients, Van den Hoogen et al. found a proportional increase in event rates in patients with increased CAC category and coronary stenosis severity. What was even more importantly noted was that patients with normal CTA had an excellent prognosis [59]. Whether or not asymptomatic diabetic patients would benefit from screening for CAD remains controversial. Muhlestein et al. demonstrated in a prospective study of 900 patients that CTA screening showed no survival benefit compared to optimized medical therapy in asymptomatic patients with type 1 and type 2 diabetes mellitus [60].


*CCTA*, coronary computed tomographic angiography; *CAD*, coronary artery disease; *HR*, hazard ratio; LAVP, low attenuation volume plaque; LAP, low attenuation plaque; MACE, major adverse cardiac events.

**Table 4.** Major studies assessing prognostic value of CCTA.

Symptomatic patients are another subgroup of patients where the role of CTA and its clinical implication was assessed. ROMICATT II and CCATCH trials [61, 62] addressed the clinical impact of CTA-guided therapy in patients with acute chest pain and negative ECG and cardiac biomarkers were evaluated in 600 randomized patients. Almost half underwent CTA guided and other half standard care (exercise MPI/EKG). MACE (cardiac death, myocardial infarction, hospitalization for unstable angina, symptom-driven revascularization, and readmission for chest pain) was significantly better in CTA group.

In conclusion, the above review has summarized the advances in CCTA and emerging data reflecting the very promising role CCTA carries in diagnosis and prognosis over the traditional risk assessment. Its unique ability to provide complete assessment of anatomy, plaque characteristics, and prognosis makes the CCTA's future very promising and crucial in enhancing patient care.

**Figure 8.** CCTA image of the coronaries with traditional plaque classification and the corresponding histology slides. There are non-calcified (A), calcified (B), and mixed plaque (C) noted. Based on plaque attenuation, there is homogeneous (D), heterogeneous (E), and napkin-ring sign (F) plaques [56].

**Figure 9.** Probability of having acute coronary syndrome during the index hospitalization according to coronary computed tomography characteristics. Central Illustration: Significant stenosis and high-risk coronary plaque features and their association with the probability of having acute coronary syndrome during the index hospitalization. Stenosis of ≥50%—Severe stenosis of the mid-left anterior descending coronary artery (Bold arrow). Non-calcified plaque with positive remodeling in the distal right coronary artery (arrowhead). Positive remodeling—The two dotted red lines (image insert) demonstrate the vessel diameters at the proximal and distal reference (both 1.8 mm) and the full red line demonstrates the maximal vessel diameter in the mid portion of the plaque (2.7 mm)—the remodeling index is 1.5 Low HU plaque—Partially calcified plaque in the mid-right coronary artery with low <30 HU plaque. The red circles demonstrate the three regions of interest with the mean CT number of 22, 19, and 20 HU Napkin-ring sign—Napkinring sign plaque in the mid-left anterior descending coronary artery. Schematic cross-sectional view of the napkinring sign. The red line demonstrates the central low HU area of the plaque adjacent to the lumen (ellipse) surrounded by a peripheral rim of the higher CT attenuation (arrows). Spotty calcium—Partially calcified plaque in the mid-right coronary artery with spotty calcification (diameter of <3 mm in all directions; circles) [58].

Symptomatic patients are another subgroup of patients where the role of CTA and its clinical implication was assessed. ROMICATT II and CCATCH trials [61, 62] addressed the clinical impact of CTA-guided therapy in patients with acute chest pain and negative ECG and cardiac biomarkers were evaluated in 600 randomized patients. Almost half underwent CTA guided and other half standard care (exercise MPI/EKG). MACE (cardiac death, myocardial infarction, hospitalization for unstable angina, symptom-driven revascularization, and read-

*CCTA*, coronary computed tomographic angiography; *CAD*, coronary artery disease; *HR*, hazard ratio; LAVP, low

attenuation volume plaque; LAP, low attenuation plaque; MACE, major adverse cardiac events.

**Study Study aim Patients (***N***) Population characteristics Major findings**

472 Acute chest pain, low risk for ACS.

previously diagnosed

1584 Suspected CAD, not

1469 Low to intermediate risk patients for CAD

1168 Patient with suspected CAD

1884 Symptomatic patient with angina-equivalent

525 Asymptomatic diabetic

600 Symptomatic patient with chest pain but negative troponin and ECG

patients with no known history of CAD

Presence of high-risk plaques was an independent *predictor* 

Severity of CAD and total plaque score predicted cardiac events over standard

Strongest predictors for MACE were LAP and napkin-ring sign with HR of 4.96 and 3.85, respectively.

Napkin-ring sign lesions and LAVP found to be predictors for MACE with LAVP carrying the strongest prognostic value HR 1.12, *p*

MACE were 5.6% in patients with non-obstructive CAD and 36.28% in patients with

*of ACS*

clinical events

< 0.0001

*p* = 0.04

obstructive CAD

Excellent prognosis in patient with CCTA negative. Prognosis was worse and directly proportional to the *number and severity of stenosis*

CCTA-guided strategy appears to improve clinical outcomes in these patient population with HR: 0.36;

In conclusion, the above review has summarized the advances in CCTA and emerging data reflecting the very promising role CCTA carries in diagnosis and prognosis over the traditional risk assessment. Its unique ability to provide complete assessment of anatomy, plaque characteristics, and prognosis makes the CCTA's future very promising and crucial in enhanc-

mission for chest pain) was significantly better in CTA group.

ing patient care.

**Puchner S. et al. [58] (ROMICATII TRIAL)**

**Hadamitzky M et al.** 

**Feuchtner G et al. [55]** Prospective

**Nadjiri J et al. [56]** Plaque

**Cheruvu C et al. [50]** Predict MACE

**Van den Hoogen IJ et al.** 

**Linde et al. [61] (CATCH TRIAL)**

**[59]**

**[48, 49]**

Plaque characteristics predicting ACS.

18 Computed Tomography - Advanced Applications

Predict cardiac events at 5 years follow-up.

assessment of the CCTA and MACE.

characteristics and associated prognosis

in long-term follow-up.

Prognostic assessment of the CCTA in patient with diabetes mellitus

CCTA-guided management and clinical outcomes.

**Table 4.** Major studies assessing prognostic value of CCTA.

**Figure 10.** An example of the quantitative plaque measurements. **Panel A** – The large coronary plaque in the proximal right coronary artery (RCA) showed in long-axis view in the multiplanar reformatted image. **Panel B** – The cross-sectional view of the proximal RCA demonstrates a large plaque. The software detects plaque components with low CT attenuation <30HU, 31 to 60HU and 61 to 130HU. **Panel C** – The curved multiplanar reformatted image of the RCA. The proximal and distal normal cross sections are selected manually by the reader to mark the beginning and end of the plaque. The software automatically selects the minimal luminal area (stenosis). **Panel D** – The software provides quantitative measurements of the selected coronary plaque including total plaque volume (127 mm3 ), remodeling index (2.04), stenosis degree (21%) and plaque length (11.7 mm). The volumes of plaque subcomponents are also reported [62].

### **Author details**

Karthik Ananthasubramaniam\*, Nishtha Sareen and Gjeka Rudin

\*Address all correspondence to: kananth1@hfhs.org

1 Department of Medicine, Heart and Vascular Institute, Henry Ford Hospital, Detroit, Michigan, USA

2 Division of Cardiology, St. Joseph Mercy Hospital Oakland, Michigan, USA

### **References**

**Author details**

Michigan, USA

Karthik Ananthasubramaniam\*, Nishtha Sareen and Gjeka Rudin

2 Division of Cardiology, St. Joseph Mercy Hospital Oakland, Michigan, USA

1 Department of Medicine, Heart and Vascular Institute, Henry Ford Hospital, Detroit,

**Figure 10.** An example of the quantitative plaque measurements. **Panel A** – The large coronary plaque in the proximal right coronary artery (RCA) showed in long-axis view in the multiplanar reformatted image. **Panel B** – The cross-sectional view of the proximal RCA demonstrates a large plaque. The software detects plaque components with low CT attenuation <30HU, 31 to 60HU and 61 to 130HU. **Panel C** – The curved multiplanar reformatted image of the RCA. The proximal and distal normal cross sections are selected manually by the reader to mark the beginning and end of the plaque. The software automatically selects the minimal luminal area (stenosis). **Panel D** – The software provides quantitative measurements of the selected

), remodeling index (2.04), stenosis degree (21%) and plaque length

\*Address all correspondence to: kananth1@hfhs.org

(11.7 mm). The volumes of plaque subcomponents are also reported [62].

coronary plaque including total plaque volume (127 mm3

20 Computed Tomography - Advanced Applications


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## **Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image**

Marcin Sawicki

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26 Computed Tomography - Advanced Applications

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68557

#### **Abstract**

Treatment planning in High Dose Rate (HDR) brachytherapy based on three‐dimen‐ sional (3D) imaging allows for prearranging and realization optimal treatment process. This process consists of procedure planning, the choice of applicators, adjusting the appropriate implantation technique, and planning of three‐dimensional distribution of dose in computerized treatment planning system. 3D images used in treatment planning in HDR brachytherapy allows for choosing the most appropriate application technique. This in turn allows for the best area coverage by reference dose with simultaneous pro‐ tection of critical organs. Treatment planning on 3D images assures individual planning of dose dispersion in target area. Several techniques will be presented based on 3D imag‐ ing in location such as lung, skin cancer, breast, and prostate cancer. For each location, relative cases will be provided where different applicators and techniques were applied. These examples are going to present images from before and after performed application along with the pictures from computer treatment planning system. In each of described locations, relative advice and rules of conducting accurate application will be provided.

**Keywords:** HDR brachytherapy, treatment planning, 3D, three‐dimensional images

### **1. Introduction**

HDR brachytherapy is a radiotherapy method in which a source of ionizing radiation is administered directly into the tumor area or to its nearest surroundings. Dissemination of this method, nowadays, is associated with the possibility of using radiation sources with rela‐ tively low dimension. Small size of capsules made administration of catheter possible in the areas where previously it would have not been possible or would have involved a number of inconveniences for the patient as well as considerable risks of complications, e.g., bronchial

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

carcinoma. This unique method also provides the possibility to determine the exact location of catheter in the tumor area for applying several visualization methods.

The purpose of the following chapter is to introduce practical application of HDR brachy‐ therapy based on the three‐dimensional (3D) computed tomography method. This publica‐ tion is for those who are interested in applying and using 3D images in HDR brachytherapy and are searching for practical treatment examples based on this method. The purpose of this section is to spread treatment HDR brachytherapy treatment planning based on 3D images. The majority of brachytherapy departments still base their treatment on 2D imaging in spite of relatively popular CT scanners.

This chapter aims to familiarize the reader with treatment planning based on CT imaging to draw attention to the benefits coming from this method not only for the treatment planning but also for the patient. It is a practical guide based on brachytherapy department experiences located in Subcarpathian Cancer Center.

This chapter includes CT images presenting brachytherapy treatment in different stages of treatment planning. It is going to introduce a course of planning process in different locations as well as the application methods used in correspondence to the location of the treatment. With each location, relevant suggestions and recommendations will be provided, which would improve the whole treatment planning process.

This chapter is mainly addressed to radiotherapy specialists but also residents, physical med‐ ics, radiologists, and everyone who is interested in the topic of applying CT imaging in HDR brachytherapy.

First section deals with what the approach of brachytherapy is and what imaging methods it uses. Also, the differences emerging from using different imaging methods and locations where 3D imaging was used will be described as well as the methods applied to enhance the treatment planning procedure. It will illustrate the guidelines we use in our department when treating different tumor locations along with the necessary equipment relevant in the 3D imaging method.

Second section will demonstrate, in detail, its applications in various locations. In this chapter, I am going to demonstrate the utilization of HDR brachytherapy in treatment of breast, pros‐ tate, skin, and lung cancers. Depending on the tumor location, one or more examples will be provided. For each case, there will be one accepted treatment plan presented. Each case includes a wide range of materials in the form of CT images and computed planning system, each of them will be described under the angle of planning and conducting in most optimal application, based on the experience of our department. I am going to present several plan‐ ning stages, starting from CT scans on different application levels to the demonstration of images and results of computer treatment planning system (TPS).

### **2. Treatment planning in brachytherapy HDR**

Brachytherapy HDR is administration of a source of ionizing radiation into the immedi‐ ate vicinity of the tumor. Because of the high gradient dose, the administered application allows for reduction of ionizing radiation in the critical organs area with simultaneous coverage of tumor area with reference dose. Treatment planning process can be based on two‐ and three‐dimensional imaging. In case of 2D imaging, distribution of dosage around the **catheter** would conventionally be calculated on X‐ray pictures taken in two different projections. This reconstruction allows us to determine the dose around the guide or guides [1]. We do not have the exact information about the dose in the target and the critical organs in the immediate vicinity to catheter. When planning a treatment, CT images provide actual information about the location of the applicator, target, and organ at risk (OAR). Images from computer tomography are electronic cross‐sections (scans) of a patient body, which includes cancerous areas. The distance between those scans is adjusted accordingly to achieve best‐possible three‐dimensional reconstruction of the patient's body. It is necessary to calculate and determine the dose on the clear scans from the CT. The dosage calculation area here is the patient's body. Second, radiation area is determined along with critical organs and structures. Using the linear method, involving manual or automatic contouring of selected areas in each scan, ionizing areas are deter‐ mined as well as critical organs and structures. Ionizing area in brachytherapy is defined by a three‐step process:


carcinoma. This unique method also provides the possibility to determine the exact location

The purpose of the following chapter is to introduce practical application of HDR brachy‐ therapy based on the three‐dimensional (3D) computed tomography method. This publica‐ tion is for those who are interested in applying and using 3D images in HDR brachytherapy and are searching for practical treatment examples based on this method. The purpose of this section is to spread treatment HDR brachytherapy treatment planning based on 3D images. The majority of brachytherapy departments still base their treatment on 2D imaging in spite

This chapter aims to familiarize the reader with treatment planning based on CT imaging to draw attention to the benefits coming from this method not only for the treatment planning but also for the patient. It is a practical guide based on brachytherapy department experiences

This chapter includes CT images presenting brachytherapy treatment in different stages of treatment planning. It is going to introduce a course of planning process in different locations as well as the application methods used in correspondence to the location of the treatment. With each location, relevant suggestions and recommendations will be provided, which

This chapter is mainly addressed to radiotherapy specialists but also residents, physical med‐ ics, radiologists, and everyone who is interested in the topic of applying CT imaging in HDR

First section deals with what the approach of brachytherapy is and what imaging methods it uses. Also, the differences emerging from using different imaging methods and locations where 3D imaging was used will be described as well as the methods applied to enhance the treatment planning procedure. It will illustrate the guidelines we use in our department when treating different tumor locations along with the necessary equipment relevant in the

Second section will demonstrate, in detail, its applications in various locations. In this chapter, I am going to demonstrate the utilization of HDR brachytherapy in treatment of breast, pros‐ tate, skin, and lung cancers. Depending on the tumor location, one or more examples will be provided. For each case, there will be one accepted treatment plan presented. Each case includes a wide range of materials in the form of CT images and computed planning system, each of them will be described under the angle of planning and conducting in most optimal application, based on the experience of our department. I am going to present several plan‐ ning stages, starting from CT scans on different application levels to the demonstration of

Brachytherapy HDR is administration of a source of ionizing radiation into the immedi‐ ate vicinity of the tumor. Because of the high gradient dose, the administered application

of catheter in the tumor area for applying several visualization methods.

of relatively popular CT scanners.

28 Computed Tomography - Advanced Applications

brachytherapy.

3D imaging method.

located in Subcarpathian Cancer Center.

would improve the whole treatment planning process.

images and results of computer treatment planning system (TPS).

**2. Treatment planning in brachytherapy HDR**

• Planning target volume (PTV)—1 cm safety margin top‐bottom in regard to CTV and addi‐ tional 1 cm resulting from uncertain location of catheter or possible applicator movements caused, i.e., transporting the patient.

As a result of reconstruction, you get a three‐dimensional image of target volume and critical organs. Application of computer treatment planning methods enables a precise dosage cal‐ culation. Dosage distribution is determined using formalism TG‐43 or Monte Carlo method. Individual treatment plan is verified before the treatment starts. Designated dosage, active length, dwell times, and source activity are being confirmed. Once all these data have been verified, the treatment plan begins to be realized.

The main purpose of treatment planning based on computed tomography images is to deter‐ mine the best‐possible dosage in the therapeutic area, simultaneously decreasing its volume in organs and critical structures. Such adjustment can be accomplished by treatment planning enhancement [2–6].

This process depends on defining the location and appropriate dwell time to achieve the desired dose distribution in the patient's body. Introduction of new 3D methods that are applied in treatment planning triggered studies on optimization algorithms using data from three‐dimensional imaging. One example is graphical optimization. Thanks to the informa‐ tion from target volume and surrounding it structures, optimization algorithm provided a possibility to target the area of interest with reference dose while protecting tissues sur‐ rounding implant. Graphical optimization allows change of shape of the isodose in any way. Applying such set of applicators enables the reduction of organ at risk (OARs) dose. Utilizing 3D imaging allows us to define the exact application place as well as determine the type and correct amount of applicators.

#### **2.1. Lung cancer**

In case of lung cancer, HDR brachytherapy treatment planning is conventionally based on two‐dimensional imaging. More and more brachytherapy departments get access to computer tomography, which provide three‐dimensional imaging. In our brachytherapy department, the entire treatment process is based on three‐dimensional imaging. Dosage distribution in treatment planning based on 2D imaging is conventionally set in reference points of axis. Reference points are identified in constant proximity from the reconstructed applicator axis, which usually is 1 cm. The applicators curvature is an important factor taken into consider‐ ation while calculating dose distribution in 3D‐based treatment. Dose disperse is set on the target area taking into consideration critical organs. Equipment routinely used for adminis‐ tering bronchial applicators in our department is a bronchovideoscope.

Before the treatment begins, the patient has computed tomography. Then, radiotherapist familiarizes themselves with the patient's history and then determines the area for adminis‐ tering the ionizing radiation.

In cases where the tumor area allows for applying the catheter into the tumor, usually only one applicator is used. In situations where the tumor location does not allow for the direct application of a catheter into the tumor area, several applicators are applied into the imme‐ diate surroundings of therapeutic area. Usage of one applicator in the tumor area does not allow for optimal coverage by the reference dose. It is caused by unsymmetrical shape of the target in the reference to the applicator. By such implantation, applicator can be the reason for a quantity that exceeds reference dose many times over. To achieve the best coverage of the tumor area, it is best to use several applicators. Applicators, as long as the clinical situation allows, are placed to be inside the tumor and in the external target area. Such treatment allows the reduction of high contact dose, which is the case when using only one applicator, as well as a considerable dose reduction in OARs.

Once application is completed, markers are injected to each of the catheters. Markers role is to visualize the catheter in which stepping source is going to maneuver. The next step is to execute CT imaging, and it is advised to perform imaging of the entire inspiration stage. Its purpose is to mineralize movement of markers during the treatment. When images indicate patients major movements while breathing, it is necessary to repeat the procedure as there is a possibility of artifacts occurring, e.g., in form of blurred images. Changes in applicator location in reference to the target caused by the patient's movement do not have a significant effect on dose dispersion in the patients system [7]. Scans are performed every 2.5 mm. In case, scans are performed below 2.5 mm proximity, the quality of images is significantly impaired.

Once CT images are accepted by radiotherapist and medical physicist, they are being sent to the computerized system of treatment planning. Radiotherapist marks each image for PTV and OARs areas. In lung cancer area, the critical organs are esophagus, heart, and spinal cord. In our department, we contour the actual image of target and critical organs on the images from computed tomography. Dose is specified for the entire PTV area. Most recent American Brachytherapy Society guidelines suggest 3D imaging for lung cancer treatment planning while applying HDR brachytherapy [8].

During the next stage, medical physicist performs reconstruction of applicators trajectory. Selection of the optimal source step and stop place in the in the nearest proximity from PTV. Then, the treatment plan is being optimized. Generally, treatment plan is optimized onto dose reference points usually situated 1 cm from catheter axis [9]. Reference dose should be calculated for the target area. This process is greatly influenced by the number of applicators. In our department, it is usually between two and four. The number of catheters adminis‐ tered depends mainly on patient's condition, location, and the volume of therapeutic area. When possible, bronchial applicators are implemented into the terminal bronchioles. Such allocation prevents catheter from sliding out what can stem from patient's couch movements caused by the presence of excrescence in patient's airways.

Routinely, treatment plans are optimized by graphical optimization. It is crucial to examine the dose dispersion in patient's system after each modification based on graphic optimization. After the development process is completed, plan is evaluated. Radiotherapist analyzes vol‐ ume dose histogram (DVH). Evaluation of target coverage by reference dose in 85, 100, and 115% volume, as well as the dose in most important critical volume structures, was done. In instances of heart, spinal cord, and esophagus, the dose examined was 0.1, 1, and 2 cm3 vol‐ ume in each of those structures. After initial DVH, the dose dispersion is determined on each cross‐section (image). After the plan is accepted, it is sent to the Treatment Control Station.

#### *2.1.1. Case*

**2.1. Lung cancer**

30 Computed Tomography - Advanced Applications

tering the ionizing radiation.

as a considerable dose reduction in OARs.

while applying HDR brachytherapy [8].

In case of lung cancer, HDR brachytherapy treatment planning is conventionally based on two‐dimensional imaging. More and more brachytherapy departments get access to computer tomography, which provide three‐dimensional imaging. In our brachytherapy department, the entire treatment process is based on three‐dimensional imaging. Dosage distribution in treatment planning based on 2D imaging is conventionally set in reference points of axis. Reference points are identified in constant proximity from the reconstructed applicator axis, which usually is 1 cm. The applicators curvature is an important factor taken into consider‐ ation while calculating dose distribution in 3D‐based treatment. Dose disperse is set on the target area taking into consideration critical organs. Equipment routinely used for adminis‐

Before the treatment begins, the patient has computed tomography. Then, radiotherapist familiarizes themselves with the patient's history and then determines the area for adminis‐

In cases where the tumor area allows for applying the catheter into the tumor, usually only one applicator is used. In situations where the tumor location does not allow for the direct application of a catheter into the tumor area, several applicators are applied into the imme‐ diate surroundings of therapeutic area. Usage of one applicator in the tumor area does not allow for optimal coverage by the reference dose. It is caused by unsymmetrical shape of the target in the reference to the applicator. By such implantation, applicator can be the reason for a quantity that exceeds reference dose many times over. To achieve the best coverage of the tumor area, it is best to use several applicators. Applicators, as long as the clinical situation allows, are placed to be inside the tumor and in the external target area. Such treatment allows the reduction of high contact dose, which is the case when using only one applicator, as well

Once application is completed, markers are injected to each of the catheters. Markers role is to visualize the catheter in which stepping source is going to maneuver. The next step is to execute CT imaging, and it is advised to perform imaging of the entire inspiration stage. Its purpose is to mineralize movement of markers during the treatment. When images indicate patients major movements while breathing, it is necessary to repeat the procedure as there is a possibility of artifacts occurring, e.g., in form of blurred images. Changes in applicator location in reference to the target caused by the patient's movement do not have a significant effect on dose dispersion in the patients system [7]. Scans are performed every 2.5 mm. In case, scans are performed below 2.5 mm proximity, the quality of images is significantly impaired. Once CT images are accepted by radiotherapist and medical physicist, they are being sent to the computerized system of treatment planning. Radiotherapist marks each image for PTV and OARs areas. In lung cancer area, the critical organs are esophagus, heart, and spinal cord. In our department, we contour the actual image of target and critical organs on the images from computed tomography. Dose is specified for the entire PTV area. Most recent American Brachytherapy Society guidelines suggest 3D imaging for lung cancer treatment planning

tering bronchial applicators in our department is a bronchovideoscope.

In this case, patient is diagnosed with an inoperable non–small cell right lung cancer. Before the treatment begins, the patient has computed tomography (**Figure 1**). Overall patient's con‐ dition and the location of changes allowed the introduction of three bronchial applicators. All applicators were in the immediate proximity to tumor area. **Figure 2** shows scans with volume target contoured in computerized treatment planning systems (TPS). Illustration from computerized planning system depicts three‐dimensional reconstruction of bronchial applicators, PTV, OARs, and dose distribution (**Figure 3**). Reconstruction on several planes and DVH is presented in **Figure 4**. The patient was treated with 18 Gy dose in three fractions.

#### *2.1.2. Case*

Second situation presents a patient with an inoperable non–small cell right lung cancer. Before the treatment begins, the patient has computed tomography. Overall patient's condition and the location of changes allowed the introduction of three bronchial applicators. Two applica‐ tors (nr1 and nr2) were introduced through the PTV area and planted in bronchial tubes. Applicator nr3 was placed where the bronchial tubes light has been blocked by the neoplastic changes. Very often, such applicator placement causes dilatation of bronchial tube, making it possible to introduce applicator through this area during next fraction. This, furthermore, improves the coverage on tumor area. **Figure 5** shows scans with volume target contoured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruc‐ tion of bronchial applicators, PTV, OARs, and dose distribution (**Figure 6**). Reconstruction on several planes and DVH is presented in **Figure 7**. The patient was treated with 18 Gy dose in three fractions. In **Figure 8**, cancer photo was captured during the application.

**Figure 1.** CT image of the front (A) and side (B) of the patient with marked PTV.

**Figure 2.** Images of the TPS with PTV.

#### **2.2. Skin cancer**

In the case of skin cancer, depending on its size and location, we can differentiate several types of applicators. With small and superficial skin changes, usually Leipzig applicators are being used. When dealing with long and flat changes, i.e., on the leg, then usually Freiburg flap is applied. The advantage of this applicator derives from the parallel posi‐ tioning of catheters and consistent length at which they are situated. The distance of the catheters from the surface is also consistent. This type of applicator is also characterized

**Figure 3.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators and OARs and 3D dose reference distribution.

by the high repetitiveness during the following irradiation fractions. The only requirement is the correct marking of applicator placement on the patient's skin. Very often, the place in which cancer is situated, i.e., in nose, ear, or cheek area, doesn't allow for application of standard applicators. In this case, it is very difficult to determine with the use of standard applicator. Using of standard applicator will not allow for ensuring optimal dose distribu‐ tion in the PTV area. It is caused by inability to adjust catheter location in reference to the target [10].

**2.2. Skin cancer**

**Figure 2.** Images of the TPS with PTV.

In the case of skin cancer, depending on its size and location, we can differentiate several types of applicators. With small and superficial skin changes, usually Leipzig applicators are being used. When dealing with long and flat changes, i.e., on the leg, then usually Freiburg flap is applied. The advantage of this applicator derives from the parallel posi‐ tioning of catheters and consistent length at which they are situated. The distance of the catheters from the surface is also consistent. This type of applicator is also characterized

**Figure 1.** CT image of the front (A) and side (B) of the patient with marked PTV.

32 Computed Tomography - Advanced Applications

Applicator adjustment during the following irradiation fractions is influenced by a consid‐ erable inaccuracy margin caused by a limited applicator placement repetitiveness in regard to patient's body. In cases when changes are located in close proximity to risk organs, appli‐ cator reconstruction can be planned so that it can decrease irradiation dose in those organs. The dose can also be reduced by appropriate arrangement of catheters in the applicator.

**Figure 4.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

```
Figure 5. Images of the TPS with PTV.
```
In cases of shallow changes, situated in immediate proximity to applicators surface, cath‐ eters can be placed slightly further away from the target to avoid high dosage besides the PTV area. However, if the cancerous region is situated underneath the layer of skin and skin itself is OAR, the applicators will be moved toward the skin surface, inside the silicone

**Figure 6.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators OARs and 3D dose reference distribution.

mask. Such applicator distribution is the reason for the high dose, and catheters being the source do not reach to skin region. Another way to dose distribution, and therefore pro‐ tection for critical organs, is the adoption of shields. Their task is to absorb (reduce) the dose, for I192 the half value is 2.5 mm for lead (HVL pb). Shields can be in the form of led strips in different thickness. Such shield can be produced in workshop of teleradiotherapy department. Shield adjustment takes place on provided patient's gypsum cast. Shields are fixed in a silicone mask with the exception of the three‐dimensional computer tomography imaging. LED shields are the source of artifacts during CT imaging, hence disturbing the treatment process. Because the individual shields are removed for the CT imaging, they are not visible on patient's scans sent to the computerized system of treatment planning. The dose that reaches critical organs protected by shields is calculated based on the thickness of applied shield. It is necessary to conduct *in vivo* dosimetry before the first irradiation to verify the prearranged dosage. Dosimetry can be conducted through applying the MOSFET detector. In cases where it is necessary to determine the dosage absorbed by an individual

In cases of shallow changes, situated in immediate proximity to applicators surface, cath‐ eters can be placed slightly further away from the target to avoid high dosage besides the PTV area. However, if the cancerous region is situated underneath the layer of skin and skin itself is OAR, the applicators will be moved toward the skin surface, inside the silicone

**Figure 4.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

**Figure 5.** Images of the TPS with PTV.

34 Computed Tomography - Advanced Applications

**Figure 7.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

**Figure 8.** Lung cancer photo.

shield, Micro‐MOSFET detectors are very effective, and because of their small‐scale dimen‐ sions, they can be placed between irradiative area and the shield itself. In cases where can‐ cerous changes are located in the area of nose or cheeks, it is advised to place such shields around patient's eyes. Such placement prevents the shield from moving while during the treatment process.

Another method of manufacturing individual applicators is the usage thermoplastic mask. Usage of the orfit masks is widely spread in teleradiotherapy. They are applied to immobilize the patient during treatment with help of external bundles. They are characterized by very good tracing qualities. Forming process takes place on patient's body. High level of its repro‐ ducibility is advantageous during the treatment process. They can be used to immobilize any location. In case of brachytherapy, such properties as reproducibility of patient's curvatures are very desirable. This is one of the reasons why I became interested in applying this type of material in the HDR brachytherapy treatment process. The concept and theory are quite simi‐ lar to silicone masks. However, there are some relevant differences between these two types of individual applicators. First, it is the use of the material itself. With the orfit mask, we get a premade product that has to be heated. When heat treated, it becomes very malleable, and after applying it onto the given surface, it easily adapts to its shape. It is setting just within few minutes. If the reproduction is not satisfying, the material can be reheated and formed again. Once it reaches ambient temperature, the mask is ready to use. Another difference lays in the way catheters are mounted to the surface of the individual applicator. With the silicone mask, applicators are inside, and with the Orfit mask, they can be freely mounted onto it. So in situ‐ ation where the applicators need to be close to the surface of the skin, we can immobilize cath‐ eters by sewing them to the mask. When they have to be further away from the surface of the orfit mask, we can use paraffin bolus or secure silicone mask. With shields, the workflow pro‐ cedure is the same as with the silicone mask. Because we use thermoplastic material, we can contour the shield placement, which allows the position control throughout every treatment fraction. The last difference between the orfit and silicone masks is the manner of mounting it onto the patient. The silicone mask uses patient's natural curvatures for the appropriate setting. In large areas, it is easy to adjust the applicator; however, in cases with flat areas, it is necessary to mark reference points on the patient's body. Additionally, for the mask to adhere properly through irradiation process, it is advisable to use immobilizing bands. The orfit mask is fixed to the base on which the patent is laid. It is mounted to specialized brackets and that is why mask adjustment is the same during every fraction. Immobilizing bands are no more necessary nor is the marking of reference points on the patient's body. Routinely, silicone masks are ready in 4 to 5 days after taking the imprint. When adopting the use of the orfit mask, first fraction can be performed on the same day that the patient is accepted to the brachytherapy department.

#### *2.2.1. Case*

**Figure 8.** Lung cancer photo.

**Figure 7.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

36 Computed Tomography - Advanced Applications

The first case presents a patient with skin cancer (squamous cell carcinoma). Cancer is located in the vicinity of the ear. The patient was qualified for treatment with the applicator indi‐ vidual (silicone mask). In the silicone mask were placed seven applicators. The patient was treated with 40 Gy in 10 fractions once a day. **Figure 9** shows scans with volume target con‐ toured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruction applicators, PTV, and dose distribution (**Figure 10**). Reconstruction on several planes and DVH is presented in **Figure 11**. Patient treated with silicone mask is presented in **Figure 12**.

### *2.2.2. Case*

The second case presents a patient with skin cancer (basal cell carcinoma). Cancer is located in the vicinity of the nose. The patient was qualified for treatment with the applicator individual (orfit mask). In the silicone mask were placed four applicators. The patient was treated with 50 Gy in 10 fractions once a day. The patient had a shield on both eyes. Before the treatment begins, the patient has computed tomography to verify the mask fit to the patient (**Figure 13**). **Figure 14** shows scans with volume target contoured in TPS. Illustration from TPS depicts three‐dimensional reconstruction applicators, PTV, OARs, and dose distribution (**Figure 15**). Reconstruction on several planes and DVH is presented in **Figure 16**. Patient treated with the orfit mask is presented in **Figure 17**.

#### *2.2.3. Case*

The third case presents a patient with skin cancer (basal cell carcinoma). Cancer is located in the vicinity of the nose. The patient was qualified for treatment with the applicator individual

**Figure 9.** Images of the TPS with PTV.

Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image http://dx.doi.org/10.5772/intechopen.68557 39

reconstruction applicators, PTV, and dose distribution (**Figure 10**). Reconstruction on several planes and DVH is presented in **Figure 11**. Patient treated with silicone mask is presented in

The second case presents a patient with skin cancer (basal cell carcinoma). Cancer is located in the vicinity of the nose. The patient was qualified for treatment with the applicator individual (orfit mask). In the silicone mask were placed four applicators. The patient was treated with 50 Gy in 10 fractions once a day. The patient had a shield on both eyes. Before the treatment begins, the patient has computed tomography to verify the mask fit to the patient (**Figure 13**). **Figure 14** shows scans with volume target contoured in TPS. Illustration from TPS depicts three‐dimensional reconstruction applicators, PTV, OARs, and dose distribution (**Figure 15**). Reconstruction on several planes and DVH is presented in **Figure 16**. Patient treated with the

The third case presents a patient with skin cancer (basal cell carcinoma). Cancer is located in the vicinity of the nose. The patient was qualified for treatment with the applicator individual

**Figure 12**.

*2.2.2. Case*

*2.2.3. Case*

orfit mask is presented in **Figure 17**.

38 Computed Tomography - Advanced Applications

**Figure 9.** Images of the TPS with PTV.

**Figure 10.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators and 3D dose reference distribution.

**Figure 11.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

**Figure 12.** Patient treated with the silicone mask.

**Figure 13.** CT image of the front (A) and side (B) of the patient with an orfit mask.

**Figure 14.** Images of the TPS with PTV.

Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image http://dx.doi.org/10.5772/intechopen.68557 41

**Figure 12.** Patient treated with the silicone mask.

40 Computed Tomography - Advanced Applications

**Figure 14.** Images of the TPS with PTV.

**Figure 13.** CT image of the front (A) and side (B) of the patient with an orfit mask.

**Figure 15.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators OARs and 3D dose reference distribution.

(Orfit mask). In the silicone mask were placed eight applicators. The patient was treated with 50 Gy in 10 fractions once a day. The patient had individual shield on one eye and standard shield on the other eye (**Figure 18**). Before the treatment begins, the patient has computed tomography to verify the mask fit to the patient (**Figure 19**). **Figure 20** shows scans with

**Figure 16.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

**Figure 17.** Patient treated with an orfit mask.

**Figure 18.** Picture of shield.

Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image http://dx.doi.org/10.5772/intechopen.68557 43

**Figure 19.** CT image of the front (A) and side (B) of the patient with an orfit mask.

**Figure 20.** Images of the TPS with PTV.

volume target contoured in TPS. Illustration from TPS depicts three‐dimensional reconstruc‐ tion applicators, PTV, OARs, and dose distribution (**Figure 21**). Reconstruction on several planes and DVH is presented in **Figure 22**. Patient treated with the orfit mask is presented in **Figure 23**

#### **2.3. Breast cancer**

**Figure 16.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

**Figure 17.** Patient treated with an orfit mask.

42 Computed Tomography - Advanced Applications

**Figure 18.** Picture of shield.

With breast cancer, brachytherapy can be applied as a method associated with teleradiother‐ apy after breast‐conserving surgery. It is realized in form of boost. It can also be applied as an independent form of post‐surgical treatment (Accelerated Partial Breast Irradiation) as an alternative to the external beam radiotherapy.

**Figure 21.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators OARs and 3D dose reference distribution.

Before breast brachytherapy treatment begins, after radical dissection, it is necessary to per‐ form tumor bed imaging. Computed tomography is the advised method to apply. Before CT examination, it is necessary to place markers on the post‐surgical scar. The presence of this marker does not have a significant effect on the quality of images from CT. It is possible to use specialized markers for CT which, because of the material they are made of, is not the source of artifacts. Markers placed on the scar allow more precise tumor bed localization and there‐ fore more precise applicator administration into the tumor bed area. The process for locating of tumor area is facilitated by surgical clips. They are easily identifiable in CT examination. Their presence allows for exact defining of targets location. We can adopt two techniques with the boost. One technique takes advantage of a frame so‐called a template; another one on the other hand uses metal needles. The choice of a given technique depends mainly on target Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image http://dx.doi.org/10.5772/intechopen.68557 45

**Figure 22.** CT images and reconstruction on several planes (A, B, C) and DVH (D).

**Figure 23.** Patient treated with an orfit mask.

Before breast brachytherapy treatment begins, after radical dissection, it is necessary to per‐ form tumor bed imaging. Computed tomography is the advised method to apply. Before CT examination, it is necessary to place markers on the post‐surgical scar. The presence of this marker does not have a significant effect on the quality of images from CT. It is possible to use specialized markers for CT which, because of the material they are made of, is not the source of artifacts. Markers placed on the scar allow more precise tumor bed localization and there‐ fore more precise applicator administration into the tumor bed area. The process for locating of tumor area is facilitated by surgical clips. They are easily identifiable in CT examination. Their presence allows for exact defining of targets location. We can adopt two techniques with the boost. One technique takes advantage of a frame so‐called a template; another one on the other hand uses metal needles. The choice of a given technique depends mainly on target

**Figure 21.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators OARs and 3D dose reference distribution.

44 Computed Tomography - Advanced Applications

location and patient's anatomical structure. If a patient has got big breasts and the tumor bed is located in the central area of the breast, then we use the template. This template consists of two plates and a connector which mounts those plates parallel within specified proxim‐ ity. The plates have openings through which applicators are put through. The number and the arrangement of the plains are the same on both plates. The distance between openings on plates is between 10 and 18 mm. The choice of the appropriate template depends on the size, positioning of the tumor bed, and patient's anatomical structure. By using templates, the position of needles is parallel. By applying the template, depending on patient's breast size, we can change its form. The breast is squeezed by the plates what can result in differences in implantation geometry. This kind of obstacle can be avoided by performing three‐dimen‐ sional imaging with already applied template. In cases where the application geometry is not satisfactory, it is possible to use a different template. Where the implant geometry is not sat‐ isfactory after application deriving from the used template, there is no possibility to change it without removing applicators.

Second technique, so‐called free hand, differs from the one already mentioned as in this case, the needles are applied without using templates. This technique requires extensive experi‐ ence from the person performing the treatment. Location of needles is not determined by the plates so they can run non parallel. Such distribution can provoke difficulties in obtain‐ ing the required spatial distribution of isodose in the target area. Creating of an acceptable computerized treatment plan by physicist requires wide experience in this type of applica‐ tion. It is simply because it is possible that some areas can occur with higher or lower dosage than the reference dosage prepared for PTV areas. This method can be successfully applied with small and average breasts. Arbitrariness in needle maneuvering in the breast allows for higher degree of risk organs protection. After applying templates, skin, as its being squeezed by plates, can move to closer proximity to the PTV area. This can cause telangiectasias in the skin area. When applicators are applied free hand, tumor beds do not change their location in reference to the skin. In cases where tumor bed is positioned in small proximity to the chest wall, it is possible to introduce applicators directly into bed area while applying the free‐hand technique. Where templates are used, structure of the plate reduces the possibility of introducing applicators in the PTV area. After deciding on palliation technique based on previously performed imaging, we can proceed to needle implantation. During application, it is possible to perform low‐dose CT in order to regulate applicator's trajectory through tumor bed area. After application is completed, it is necessary to secure the needles from moving out by applying clips onto them. It is particularly important when taking advantage of this technique, but it also secures the needles from relocation while attaching transfer tubes. It is crucial to remove mandrins from the needles as they are the source of numerous artifacts in computer tomography imaging. They significantly affect the image quality especially because they are in the PTV area.

In case of brachytherapy as an independent form of treatment, we can use several differ‐ ent applicators. As with the boost, we can apply plate/template techniques. The difference between boost procedures and unassisted treatment lies mainly in the number of fractions. Boost is applied in one of the fractions whereas Accelerated Partial Breast Irradiation (APBI) in eight fractions. Because of that, all metal needles have been replaced with plastic guides, which remain in patient's body through the whole treatment process. The guides are closed up with clips on the one end, whereas on the other end, we can find a connector that mounts introduced needle. Plastic needle is present in patient's body only during irradiation; they are being removed once irradiation has been completed. Because those needles are made of plastic, it is necessary to introduce dedicated markers to make them visible in CT imaging. Another method applied is so‐called balloon method which takes advantage of SAVI appli‐ cator. This applicator consists of several channels with in its central part and rest in its cir‐ cumferential area. To be able to apply this applicator, the patient has to be operated for open cavity surgery. After introducing applicator into tumor bed, it is being adjusted by dilating channels located on its boarders (circumferentially). Applicator is monitored by ultrasonogra‐ phy (USG) while being introduced; then, thee‐dimensional imaging is performed. Before CT examination, it is important to mark one of the channels on patient's body to be able to verify applicator's location in reference to the tumor bed. Verification should be taken place before each and every irradiation fraction. The applicator is introduced into patient's body for the whole time of treatment process. Breast cancer treatment process based on three‐dimensional images allows you to determine the dosage for the actual PTV area. Taking advantage of com‐ puter tomography made it possible to search for new types of applicators, which, in course, allows to cover the desirable target area and protection of critical organs. TPS images present marked the target and all risk organs. Reference dose is specified for the whole PTV area, and risk organs in this case are skin area and the wall of the chest. In case of boost, the dosage equals 10 Gy, and in case of APBI/SAVI, it is 4 Gy 8 times twice a day [11].

#### *2.3.1. Case*

location and patient's anatomical structure. If a patient has got big breasts and the tumor bed is located in the central area of the breast, then we use the template. This template consists of two plates and a connector which mounts those plates parallel within specified proxim‐ ity. The plates have openings through which applicators are put through. The number and the arrangement of the plains are the same on both plates. The distance between openings on plates is between 10 and 18 mm. The choice of the appropriate template depends on the size, positioning of the tumor bed, and patient's anatomical structure. By using templates, the position of needles is parallel. By applying the template, depending on patient's breast size, we can change its form. The breast is squeezed by the plates what can result in differences in implantation geometry. This kind of obstacle can be avoided by performing three‐dimen‐ sional imaging with already applied template. In cases where the application geometry is not satisfactory, it is possible to use a different template. Where the implant geometry is not sat‐ isfactory after application deriving from the used template, there is no possibility to change it

Second technique, so‐called free hand, differs from the one already mentioned as in this case, the needles are applied without using templates. This technique requires extensive experi‐ ence from the person performing the treatment. Location of needles is not determined by the plates so they can run non parallel. Such distribution can provoke difficulties in obtain‐ ing the required spatial distribution of isodose in the target area. Creating of an acceptable computerized treatment plan by physicist requires wide experience in this type of applica‐ tion. It is simply because it is possible that some areas can occur with higher or lower dosage than the reference dosage prepared for PTV areas. This method can be successfully applied with small and average breasts. Arbitrariness in needle maneuvering in the breast allows for higher degree of risk organs protection. After applying templates, skin, as its being squeezed by plates, can move to closer proximity to the PTV area. This can cause telangiectasias in the skin area. When applicators are applied free hand, tumor beds do not change their location in reference to the skin. In cases where tumor bed is positioned in small proximity to the chest wall, it is possible to introduce applicators directly into bed area while applying the free‐hand technique. Where templates are used, structure of the plate reduces the possibility of introducing applicators in the PTV area. After deciding on palliation technique based on previously performed imaging, we can proceed to needle implantation. During application, it is possible to perform low‐dose CT in order to regulate applicator's trajectory through tumor bed area. After application is completed, it is necessary to secure the needles from moving out by applying clips onto them. It is particularly important when taking advantage of this technique, but it also secures the needles from relocation while attaching transfer tubes. It is crucial to remove mandrins from the needles as they are the source of numerous artifacts in computer tomography imaging. They significantly affect the image quality especially because

In case of brachytherapy as an independent form of treatment, we can use several differ‐ ent applicators. As with the boost, we can apply plate/template techniques. The difference between boost procedures and unassisted treatment lies mainly in the number of fractions. Boost is applied in one of the fractions whereas Accelerated Partial Breast Irradiation (APBI) in eight fractions. Because of that, all metal needles have been replaced with plastic guides,

without removing applicators.

46 Computed Tomography - Advanced Applications

they are in the PTV area.

The first case presents a patient with breast cancer. The patient is after conservative treatment. Treatment is realized in the form of boost after external beam radiotherapy. The patient was treated with 10 Gy in 1 fraction. Before the treatment begins, the patient has computed tomog‐ raphy (**Figure 24**).The patient was treated with template. In the tumor bed were placed five applicators. **Figure 25** shows scans with volume target contoured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruction applicators, PTV, and dose distribution (**Figure 26**). Reconstruction on several planes and DVH is presented in **Figure 27**.

#### *2.3.2. Case*

The second case presents a patient with breast cancer. Patient is after breast‐conserving sur‐ gery. Treatment is realized in the form of boost after external beam radiotherapy. The patient was treated with 10 Gy in 1 fraction. Before the treatment begins, the patient has computed tomography (**Figure 28**). The patient was treated with the free‐hand technique. In the tumor bed were placed eight applicators. **Figure 29** shows scans with volume target contoured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruc‐ tion applicators, PTV, and dose distribution (**Figure 30**). Reconstruction on several planes and DVH is presented in **Figure 31**. Patient with breast cancer treated using the free‐hand technique is presented in **Figure 32**.

**Figure 24.** CT image before application with a marked scar.

**Figure 25.** Images of the TPS with PTV.

#### *2.3.3. Case*

The third case presents a patient with breast cancer. Patient is after breast‐conserving sur‐ gery. Treatment is realized in the form of post‐surgical treatment (Accelerated Partial Breast Irradiation). The patient was treated with 32 Gy in eight fractions twice a day. Before the treat‐ ment begins, the patient has computed tomography (**Figure 33**). In the tumor bed were placed 12 applicators. **Figure 34** shows scans with volume target contoured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruction applicators, PTV, and dose distribution (**Figure 35**). Reconstruction on several planes and DVH is presented in **Figure 36**.

Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image http://dx.doi.org/10.5772/intechopen.68557 49

**Figure 26.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators OARs and 3D dose reference distribution.

#### *2.3.4. Case*

*2.3.3. Case*

**Figure 25.** Images of the TPS with PTV.

**Figure 24.** CT image before application with a marked scar.

48 Computed Tomography - Advanced Applications

in **Figure 36**.

The third case presents a patient with breast cancer. Patient is after breast‐conserving sur‐ gery. Treatment is realized in the form of post‐surgical treatment (Accelerated Partial Breast Irradiation). The patient was treated with 32 Gy in eight fractions twice a day. Before the treat‐ ment begins, the patient has computed tomography (**Figure 33**). In the tumor bed were placed 12 applicators. **Figure 34** shows scans with volume target contoured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruction applicators, PTV, and dose distribution (**Figure 35**). Reconstruction on several planes and DVH is presented

The fourth case presents a patient with breast cancer. Patient is after breast‐conserving sur‐ gery. Treatment is realized in the form of post‐surgical treatment (Accelerated Partial Breast Irradiation). The patient was treated with 34 Gy in 10 fractions twice a day. Patient was treated by using applicator SAVI. Before the treatment begins, the patient has computed tomography

**Figure 27.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

**Figure 28.** CT images before application with a marked scar.

(**Figure 37**). In the tumor bed was placed one applicator with seven channels. **Figure 38** shows scans with volume target contoured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruction applicators, PTV, and dose distribution (**Figure 39**). Reconstruction on several planes and DVH is presented in **Figure 40**.

Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image http://dx.doi.org/10.5772/intechopen.68557 51

**Figure 29.** Images of the TPS with PTV.

(**Figure 37**). In the tumor bed was placed one applicator with seven channels. **Figure 38** shows scans with volume target contoured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruction applicators, PTV, and dose distribution (**Figure 39**).

Reconstruction on several planes and DVH is presented in **Figure 40**.

**Figure 28.** CT images before application with a marked scar.

**Figure 27.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

50 Computed Tomography - Advanced Applications

**Figure 30.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators OARs and 3D dose reference distribution.

**Figure 31.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

**Figure 32.** Patient with breast cancer treated using the free‐hand technique.

**Figure 33.** CT images before application with a marked scar.

Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image http://dx.doi.org/10.5772/intechopen.68557 53

**Figure 34.** Images of the TPS with PTV.

**Figure 31.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

52 Computed Tomography - Advanced Applications

**Figure 32.** Patient with breast cancer treated using the free‐hand technique.

**Figure 33.** CT images before application with a marked scar.

**Figure 35.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators OARs and 3D dose reference distribution.

**Figure 36.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

**Figure 37.** CT images before application with a marked scar.

#### **2.4. Prostate cancer**

Standard hospitalization procedure for patients suffering from prostate cancer in HDR brachytherapy is ultrasonographic imaging. Applicators used for the treatment are metal and plastic needles. Images are generated by Transrectal Ultrasound Scan (TRUS). Normally, the treatment kit consists of a transrectal probe that is mounted onto so‐called stepper. A stepper is a set of mechanical lever system, a specialized stand with longitudinal boat for USG head at Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image http://dx.doi.org/10.5772/intechopen.68557 55

**Figure 38.** Images of the TPS with PTV.

**2.4. Prostate cancer**

**Figure 37.** CT images before application with a marked scar.

Standard hospitalization procedure for patients suffering from prostate cancer in HDR brachytherapy is ultrasonographic imaging. Applicators used for the treatment are metal and plastic needles. Images are generated by Transrectal Ultrasound Scan (TRUS). Normally, the treatment kit consists of a transrectal probe that is mounted onto so‐called stepper. A stepper is a set of mechanical lever system, a specialized stand with longitudinal boat for USG head at

**Figure 36.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

54 Computed Tomography - Advanced Applications

**Figure 39.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators OARs and 3D dose reference distribution.

**Figure 40.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

its peak. During treatment, stepper was immobilized by being fixed to the floor. This prevents potential twists as well as target volume reading errors through planning system. Important function of the stepper was support of special ceramic targeting plate (template) and ultra‐ sonographic head. This plate has a grid of coordinate system correlating to this equivalently in the planning system. It is setting distance between the needles and the correct direction of the needle applicators is established. Gland images acquired from the ultrasonograph (1 mm intervals) were sent to the planning system simultaneously (on‐line), enabling real‐life change in volume target irradiation in reference to metal applicators and neighboring organs.

Prostate cancer can also be treated with means of HDR brachytherapy based on three‐dimen‐ sional imaging from computer tomography. In this case, the procedure is more complicated compared to applying TRUS. This technique is usually applied with patients who already went through surgery where rectum was removed along the cancerous tumor. It is not pos‐ sible to introduce transrectal probe after having undergone Miles surgery. Treatment is con‐ ducted with the help of computer tomography. We do not have an online preview while inserting catheters into the prostate area. The patient is laid in lateral position and not, as it is for standard treatment, in gynecological position. The reason for this comes from the fact that the treatment itself takes place on computer tomography. With patient laid like that, we can introduce applicators and perform CT imaging. They do not have to change the posi‐ tion between application and imaging processes. Hence, the danger of applicator relocation caused by patient's movement is eliminated. Furthermore, the position and inability to apply the stepper exclude the option of applying the ceramic plate. The needles are reviewed in the free‐hand technique. Before the treatment begins, a three‐dimensional imaging is performed to determine target's location as well as its volume. After the analysis of 3D images, the depth to which applicators will be introduced into patient's body can be determined. After first few needles have been applied, another computer tomography is performed to examine applica‐ tion geometry. The location as well as the depth, to which applicators have been introduced, is being inspected. Verification scheme is repeated after applying few applicators. After the application process is completed, a CT imaging is performed. Then, the images are sent to TPS with marked PTV and OAR areas. Prostate treatment planning based on CT imaging requires great experience from radiotherapist while introducing the needles into the prostate area. Medical physicists have to possess a wide experience in this type of procedures. In cases where needles are injected "free hand," it is common for catheters to intersect in patient's body, what in consequence can lead to difficulties when identifying individual applicators [12].

### *2.4.1. Case*

its peak. During treatment, stepper was immobilized by being fixed to the floor. This prevents potential twists as well as target volume reading errors through planning system. Important function of the stepper was support of special ceramic targeting plate (template) and ultra‐ sonographic head. This plate has a grid of coordinate system correlating to this equivalently in the planning system. It is setting distance between the needles and the correct direction of the needle applicators is established. Gland images acquired from the ultrasonograph (1 mm intervals) were sent to the planning system simultaneously (on‐line), enabling real‐life change

**Figure 40.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

56 Computed Tomography - Advanced Applications

in volume target irradiation in reference to metal applicators and neighboring organs.

Prostate cancer can also be treated with means of HDR brachytherapy based on three‐dimen‐ sional imaging from computer tomography. In this case, the procedure is more complicated compared to applying TRUS. This technique is usually applied with patients who already went through surgery where rectum was removed along the cancerous tumor. It is not pos‐ sible to introduce transrectal probe after having undergone Miles surgery. Treatment is con‐ ducted with the help of computer tomography. We do not have an online preview while inserting catheters into the prostate area. The patient is laid in lateral position and not, as it is for standard treatment, in gynecological position. The reason for this comes from the fact that the treatment itself takes place on computer tomography. With patient laid like that, we can introduce applicators and perform CT imaging. They do not have to change the posi‐ tion between application and imaging processes. Hence, the danger of applicator relocation caused by patient's movement is eliminated. Furthermore, the position and inability to apply the stepper exclude the option of applying the ceramic plate. The needles are reviewed in the free‐hand technique. Before the treatment begins, a three‐dimensional imaging is performed to determine target's location as well as its volume. After the analysis of 3D images, the depth to which applicators will be introduced into patient's body can be determined. After first few The first case presents a patient with prostate cancer. Miles operation is a surgery for rectal cancer or anal cancer. The patient was treated with 30 Gy in two fractions twice a day. During application, the patient had twice CT examination for verification (**Figure 41**). In the tumor bed were placed 12 applicators. **Figure 42** shows scans with volume target contoured in TPS. Illustration from computerized planning system depicts three‐dimensional reconstruction applicators, PTV, and dose distribution (**Figure 43**). Reconstruction on several planes and DVH is presented in **Figure 44**.

**Figure 41.** CT images: first imaging (A, B) and second imaging (C, D).

**Figure 42.** Images of the TPS with PTV.

**Figure 43.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators and 3D dose reference distribution.

**Figure 44.** CT images and reconstruction on several planes (A, B, and C) and DVH (D).

### **3. Summary**

**Figure 42.** Images of the TPS with PTV.

58 Computed Tomography - Advanced Applications

**Figure 43.** 3D reconstruction (A, C: front; B, D: side) of PTV applicators and 3D dose reference distribution.

Treatment planning in HDR brachytherapy based on three‐dimensional imaging allows for prearranging and conducting optimal treatment in a given location. Routinely, in parts like the lung or esophagus, treatment plan is based on 2D imaging. Academic literature provides reports about incorporating 3D along with 2D imaging in lung cancer treatment. Significant differences are also pointed out when it comes to the coverage of the therapeutic area between these two methods. Thanks to the use of computer tomography, we have got the precise loca‐ tion of the irradiation area. We can adjust the most appropriate technique and applicators to conduct the most optimal treatment. What's more, the geometry of introduced implant allows for the ultimate target coverage with simultaneous protection of organs at risk

Utilizing three‐dimensional imaging provides great possibility for treatment in location where previous access was hindered or impossible because of patient's anatomical structure or previously undergone procedures, i.e., Miles surgery.

Computer tomography allows for establishing individual treatment solutions that provide optimal approach to every patient as in skin cancer. With more and easier access to three‐ dimensional imaging, new ways of applying HDR brachytherapy open in new location as well as in form of radical treatment. With the use of imaging, we are now able to introduce catheters precisely into the tumor area with putting the patient at risk of posttreatment com‐ plications. It allows the treatment of people that no more qualify for other forms of treatment (radiotherapy). Because of the high gradient dose in HDR brachytherapy and patients with internal intracranial implants, i.e., pacemaker or cardioverter‐defibrillator, we know exactly the dose the device will receive, so we can perform the procedures without exposing the patient to additional risk. Thanks to different optimization forms based on 3D images, HDR brachytherapy is applied not only in palliative treatment but also in new ways of radical treat‐ ment, i.e., in case of APBI.

### **Author details**

Marcin Sawicki

Address all correspondence to: savi8307@poczta.fm

Brachytherapy Department, Subcarpathian Cancer Center, Brzozów, Poland

### **References**


[10] Kowalik L, Lyczek J, Sawicki M, Kazalski D. Individual applicator for brachytherapy for various sites of superficial malignant lesions. Journal of Contemporary Brachytherapy. 2013;**5**(1):45‐49

the dose the device will receive, so we can perform the procedures without exposing the patient to additional risk. Thanks to different optimization forms based on 3D images, HDR brachytherapy is applied not only in palliative treatment but also in new ways of radical treat‐

ment, i.e., in case of APBI.

60 Computed Tomography - Advanced Applications

Address all correspondence to: savi8307@poczta.fm

Contemporary Brachytherapy. 2014;**6**(3):289‐292

Physics of Radiation Therapy. LWW, Gdańsk; 2009

Brachytherapy Department, Subcarpathian Cancer Center, Brzozów, Poland

[1] Makarewicz R, editor. Brachyterapia HDR. Via Medica, Gdańsk; 2004

[2] Sawicki M. The evaluation of treatment plans in high‐dose‐rate endobronchial brachy‐ therapy by utilizing 2D and 3D computed tomography imaging methods. Journal of

[3] Zvonarev PS. 2D/3D registration algorithm for lung brachytherapy. Medical Physics.

[4] Khan FM, Gibbons J, Mihailidis D, Alkhatib H, Khan's Lectures: Handbook of the

[5] Melhus CS, Rivard MJ. Approaches to calculating AAPM TG‐43 brachytherapy dosim‐ etry parameters for Cs, I, Ir, Pd, and Yb sources. Medical Physics. 2006;**33**:1729

[6] Pérez‐Calatayud J, Granero D, Casal E, Ballester F, Puchades V. Monte Carlo and experi‐ mental derivation of TG43 dosimetric parameters for CSM‐type Cs‐137 sources. Medical

[7] Cavanaugh SX, Vidovic A, Law T, Bechara R, Parks C, Wei J, Swanson J. Multichannel endobronchial HDR catheter respiratory motion and resultant dosimetric variation.

[8] Stewart A, et al. American Brachytherapy Society consensus guidelines for thoracic

[9] Łyczek J, et al. Comparison of the GTV coverage by PTV and isodose of 90% in 2D and 3D planning during endobronchial brachytherapy in the palliative treatment of patients with advanced lung cancer. Pilot study. Journal of Contemporary Brachytherapy.

brachytherapy for lung cancer. Brachytherapy. 2016;**15**(1):1‐11

**Author details**

Marcin Sawicki

**References**

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2012;**4**:113‐115


## **Computed Tomography: Role in Femoroacetabular Impingement**

Maximiliano Barahona, Jaime Hinzpeter and Cristian Barrientos

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68558

#### **Abstract**

Femoroacetabular impingement (FAI) physiopathology is still unclear; however, there is a consensus that a pathological mechanical contact between the femoral neck-head junction and the acetabulum leads to pain and cartilage damage. Computed tomography (CT) is useful in FAI diagnosis and surgical planning. In the present chapter, we will analyze the role of CT in FAI, with special emphasis on alignment and comparison of measurements related to epidemiological variables. We analyzed 101 CT of patients that consulted in our institution for a non-joint-or-bone-related reason. Prior to the measurement of acetabular variables, CT image must be corrected in three planes. Acetabular version is a gender- and age-related measurement. As age increased, acetabular version increased, and the same impact age has on Wiberg angle. Femoral FAI-related measurement is not related to epidemiological variables. CT has a very important role for a better understanding of hip anatomy, and further research using CT images should be encouraged.

**Keywords:** femoroacetabular impingement, computed tomography, femoral alpha angle, acetabular version angle, Wiberg angle

### **1. Introduction**

Femoroacetabular impingement (FAI) is a relatively new pathology, described in the early 1990s. FAI physiopathology is still unclear; however, there is a consensus that a pathological mechanical contact between the femoral neck-head junction and the acetabulum leads to pain, microinstability, joint cartilage damage and labrum tear. FAI diagnosis should be based on clinical evaluation and subsequent appropriate radiological confirmation that aim to detect excessive femoral head coverage (pincer-type) and/or insufficient femoral head-neck offset hip (cam-type) [1–3].

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Computed tomography (CT) is a very useful tool in the diagnosis and surgical planning for FAI; however, normal values have not been still defined and lesser is the relation of these measurements according to gender, age weight and height [4–6].

In the present chapter, we will analyze the role of CT in FAI, with special emphasis on alignment and comparison of measurements related to gender, weight, height and age.

### **2. Methods**

We analyzed 101 CT of patients that consulted in our institution for a non-joint-or-bonerelated reason and who required an abdominal and pelvic CT for diagnosis. Before enrollment, volunteers completed a questionnaire, which included asking for current or historic hip-related pain and hip surgery. Positive answers led to the volunteers being excluded from the study.

In this population of 101 patients, we will perform an analysis regarding different situations related to femoroacetabular impingement in which CT has a fundamental role.

The images were obtained using a Siemens Multicut Computerized Tomography Machine, a model of Somaton Sensation 64®. In the study, a protocol of 1.5-mm cuts for every 0.3 mm was used, information that was later processed to 3-mm multiplanar reconstructions in bone window and 3D reconstructions, processed with 3D and INSPACE®, respectively.

### **3. CT radiological measures related to FAI**

### **3.1. Acetabular version**

The acetabular version is described as the acetabular orientation regarding the sagittal plane. It is considered normal that the acetabulum has an anterior orientation called anteversion [7].

The measurement is performed in an image obtained in CT in axial reconstruction. The angle is measured by drawing a line from the anterior border to the posterior border of the ipsilateral acetabulum and another vertical line which runs from the posterior edge of the acetabulum and is tangential to a horizontal line joining the posterior edges of the acetabulum (**Figure 1**). The measurement taken at the height where the acetabulum is deeper or in which the medial wall of the acetabulum is deeper corresponds to the "classic" measurement described for the diagnosis of acetabular dysplasia. It's considered retroversion when the angle is ≤15° [8, 9].

### **3.2. Crossover sign**

In a regular pelvis, the acetabulum is in anteversion so in an anterior-posterior (AP) X-ray and in a transparent reconstruction of a CT that simulates an AP X-ray, the anterior wall of the

**Figure 1.** It shows acetabular version angle measurement. It is measured by drawing a line from the anterior border to the posterior border of the ipsilateral acetabulum and another vertical line, which runs from the posterior edge of the acetabulum and is tangential to a horizontal line joining the posterior edges of the acetabulum.

acetabulum is always medial to the edge of the posterior wall. The sign is positive if in some portion the anterior border becomes lateral to the posterior border (**Figure 2**). This translates into an acetabular retroversion at the height where the crossover occurs and is associated with anterior focal over-coverage [9].

### **3.3. Center edge or Wiberg angle**

Computed tomography (CT) is a very useful tool in the diagnosis and surgical planning for FAI; however, normal values have not been still defined and lesser is the relation of these

In the present chapter, we will analyze the role of CT in FAI, with special emphasis on alignment

We analyzed 101 CT of patients that consulted in our institution for a non-joint-or-bonerelated reason and who required an abdominal and pelvic CT for diagnosis. Before enrollment, volunteers completed a questionnaire, which included asking for current or historic hip-related pain and hip surgery. Positive answers led to the volunteers being excluded from

In this population of 101 patients, we will perform an analysis regarding different situations

The images were obtained using a Siemens Multicut Computerized Tomography Machine, a model of Somaton Sensation 64®. In the study, a protocol of 1.5-mm cuts for every 0.3 mm was used, information that was later processed to 3-mm multiplanar reconstructions in bone

The acetabular version is described as the acetabular orientation regarding the sagittal plane. It is considered normal that the acetabulum has an anterior orientation called anteversion [7]. The measurement is performed in an image obtained in CT in axial reconstruction. The angle is measured by drawing a line from the anterior border to the posterior border of the ipsilateral acetabulum and another vertical line which runs from the posterior edge of the acetabulum and is tangential to a horizontal line joining the posterior edges of the acetabulum (**Figure 1**). The measurement taken at the height where the acetabulum is deeper or in which the medial wall of the acetabulum is deeper corresponds to the "classic" measurement described for the diagnosis of acetabular dysplasia. It's considered retroversion when the

In a regular pelvis, the acetabulum is in anteversion so in an anterior-posterior (AP) X-ray and in a transparent reconstruction of a CT that simulates an AP X-ray, the anterior wall of the

related to femoroacetabular impingement in which CT has a fundamental role.

window and 3D reconstructions, processed with 3D and INSPACE®, respectively.

**3. CT radiological measures related to FAI**

measurements according to gender, age weight and height [4–6].

**2. Methods**

64 Computed Tomography - Advanced Applications

the study.

**3.1. Acetabular version**

angle is ≤15° [8, 9].

**3.2. Crossover sign**

and comparison of measurements related to gender, weight, height and age.

The acetabular center-border angle is measured on an anteroposterior X-ray or in the reconstruction of a CT that simulates an AP X-ray.

From the center of the femoral head, a line is drawn that goes to the edge of the acetabulum. The other line is a vertical line from the center of the femoral head, which is perpendicular to a horizontal line passing between the ischial tuberosities (**Figure 3**). A Wiberg angle is considered normal between 20 and 40°; angles less than 20° are associated with hip dysplasia. Angles greater than 40° are associated with deep thigh and therefore there is global overcoverage [8].

### **3.4. Femoral alpha angle**

It is an angle formed at the intersection of a line that goes from the axis of the femoral neck and another line extending from the center of the femoral head to the point where a circumference, imagined on the femoral head, is intercepted with the anterior perimeter of the femoral neck (**Figure 4**) [10].

**Figure 2.** It shows a crossover sign. In a normal AP view of the pelvis, the anterior wall of the acetabulum is always medial to the edge of the posterior wall (A). It is positive when the posterior wall becomes medial to the anterior wall of the acetabulum (B).

The normal value of this angle is controversial, even more controversial than the value that must be considered pathological. Notzli et al. [11], in a paper from 2002, suggests 50% as a pathological value in a study that was performed by measuring the alpha angle in magnetic resonance imaging (MRI) and in which only the average difference test was applied between the groups. Tannast et al. [9], in a review published in 2007, uses the same value but now in CT.

Beaulé et al. [4] proposed a 50.5° CT cutoff value in a study in which they compared symptomatic and asymptomatic patients. Five years later, he published an article in which he points

**Figure 3.** It shows Wiberg angle measurement. It is considered normal between 20 and 40°.

**Figure 4.** The alpha angle was measured in an axial oblique cut of the neck. The normal value of this angle is controversial.

out that in MRI the average alpha angle in asymptomatic patients is 50.15° [12]. Allen et al., on X-rays and Kang et al., in CT, arbitrarily define the angle value at 55.5 and 55°, respectively, as pathological, arguing the findings in asymptomatic and inter-intraobserver measurement variability [8, 13].

In a study carried out by our working group, it was determined that if the cutoff value was 50° in CT, 28% of the asymptomatic population should be classified with a pathological alpha value [14]. Finally, Pollard et al. [15], in 2010, in a study carried out on X-rays, establishes that the normal average value of the alpha angle is 95% between 46 and 49°, that is, very close to the 50° proposed.

The normal value of this angle is controversial, even more controversial than the value that must be considered pathological. Notzli et al. [11], in a paper from 2002, suggests 50% as a pathological value in a study that was performed by measuring the alpha angle in magnetic resonance imaging (MRI) and in which only the average difference test was applied between the groups. Tannast et al. [9], in a review published in 2007, uses the same value but now in CT. Beaulé et al. [4] proposed a 50.5° CT cutoff value in a study in which they compared symptomatic and asymptomatic patients. Five years later, he published an article in which he points

**Figure 3.** It shows Wiberg angle measurement. It is considered normal between 20 and 40°.

**Figure 2.** It shows a crossover sign. In a normal AP view of the pelvis, the anterior wall of the acetabulum is always medial to the edge of the posterior wall (A). It is positive when the posterior wall becomes medial to the anterior wall of

the acetabulum (B).

66 Computed Tomography - Advanced Applications

The initial studies that established pathological cutoff values between 50 and 55° for the alpha angle have been invalidated by subsequent studies in healthy populations in which higher values have been found for the angle described by Notzli; in addition, they lack the methodology suitable for setting cut values in diagnostic tests [11].

We conducted an investigation in which our cohort of 101 asymptomatic patients was compared to a cohort of patients who were operated on with femoroacetabular impingement. This cohort presented hip pain referred to the inguinal region, positive flexion adduction internal rotation (FADIR) on physical examination and positive lidocaine test. In our center, the lidocaine test is performed by a radiologist specialized in the musculoskeletal region, who, under ultrasound, infiltrates intra-articular lidocaine. Before and after infiltration, a FADIR test is performed and the test is considered positive when the patient subjectively reported a decrease of more than 50% of the pain. In addition, it was considered as an inclusion requirement, the presence of intraoperative bump. Patients with previous hip surgeries, with a history of hip dysplasia, and in whom only acetabular surgical gestures were performed, were excluded.

The alpha angle was measured in an axial oblique cut of the neck, determining three levels, cephalic third, middle and caudal femoral neck, and measurements were made in the center of these levels. The measurement performed in the middle third was compared for the purposes of this study. In the case of controls, the measurement was performed on both hips and the average between right and left was registered. Regarding the cases, the value of the angle of the operated hip was registered.

A logistic regression model was estimated, in which the presence of FAI (case/control) was used as the dependent variable and the alpha angle measurement as the independent variable. A Hosmer-Lemeshow goodness-of-fit test was done to test logistic regression assumptions (this is considered appropriate if p > 0.15) [16]. The receiver operating characteristics (ROC) curve was calculated and interpreted according to Hosmer and Lemeshow recommendations [17, 18]. A significance level of 0.05 was established and 95% confidence interval is reported. All analyses were performed using Stata v11.2 (StataCorp LP, College Station, Texas, USA).

Nearly, 38 patients with femoroacetabular impingement were recruited, who had an alpha angle of 66.78° (±12.23°), while the cohort of 101 asymptomatic patients had an average alpha angle of 47.81° (±5.30°). The relationship between controls and cases is 3:1.

When estimating a logistic regression model, an odds ratio of 1.28 [1.18–1.39] was obtained, which implies that as the alpha angle measurement increases 1°, the risk of having FAI type cam increases by 28% compared to having 1° less.

The ROC curve has an area under the curve of 0.96 [0.93–0.99], which gives an excellent level of discrimination. The angle of 57° is the value that maximizes the sensitivity 92.11% and the specificity 95.05%, correctly classifying 94% of our sample.

The study by Sutter et al. [19] included 53 healthy individuals and 53 pathological patients, measuring the alpha angle in different time radii, finding a sensitivity between 72 and 76% and specificity between 73 and 80%, with an angle of 60° as the cut in the anterosuperior region. This finding is similar to that found in our work in which the cut value is higher than the 50–55° angle proposed initially and uses a similar methodology. However, the measurement of the alpha angle in radians is not the measurement that is used daily in clinical practice; it is more commonly used for research purposes, and in the relation, they used one control for each case.

The value of the alpha angle measured in an axial oblique femoral neck reconstruction has a high discriminative power for the diagnosis of symptomatic FAI type cam. The finding of an alpha angle value above 57° is suggestive of symptomatic FAI type cam.

### **3.5. Femoral offset**

The femoral head-neck offset is the distance between the anterior margin of the femoral neck and the anterior margin of the femoral head (**Figure 5**). As the sphere shape of the femoral head is lost, the offset decreases, and so it is a measure related to FAI type cam. Kang et al. [8] report that an offset smaller than 8 mm is considered pathological, whereas Tannast et al. [9] mention that a distance less than 10 mm is related to FAI.

of this study. In the case of controls, the measurement was performed on both hips and the average between right and left was registered. Regarding the cases, the value of the angle of

A logistic regression model was estimated, in which the presence of FAI (case/control) was used as the dependent variable and the alpha angle measurement as the independent variable. A Hosmer-Lemeshow goodness-of-fit test was done to test logistic regression assumptions (this is considered appropriate if p > 0.15) [16]. The receiver operating characteristics (ROC) curve was calculated and interpreted according to Hosmer and Lemeshow recommendations [17, 18]. A significance level of 0.05 was established and 95% confidence interval is reported. All analyses were performed using Stata v11.2 (StataCorp LP, College Station,

Nearly, 38 patients with femoroacetabular impingement were recruited, who had an alpha angle of 66.78° (±12.23°), while the cohort of 101 asymptomatic patients had an average alpha

When estimating a logistic regression model, an odds ratio of 1.28 [1.18–1.39] was obtained, which implies that as the alpha angle measurement increases 1°, the risk of having FAI type

The ROC curve has an area under the curve of 0.96 [0.93–0.99], which gives an excellent level of discrimination. The angle of 57° is the value that maximizes the sensitivity 92.11% and the

The study by Sutter et al. [19] included 53 healthy individuals and 53 pathological patients, measuring the alpha angle in different time radii, finding a sensitivity between 72 and 76% and specificity between 73 and 80%, with an angle of 60° as the cut in the anterosuperior region. This finding is similar to that found in our work in which the cut value is higher than the 50–55° angle proposed initially and uses a similar methodology. However, the measurement of the alpha angle in radians is not the measurement that is used daily in clinical practice; it is more commonly used for research purposes, and in the relation, they used one

The value of the alpha angle measured in an axial oblique femoral neck reconstruction has a high discriminative power for the diagnosis of symptomatic FAI type cam. The finding of an

The femoral head-neck offset is the distance between the anterior margin of the femoral neck and the anterior margin of the femoral head (**Figure 5**). As the sphere shape of the femoral head is lost, the offset decreases, and so it is a measure related to FAI type cam. Kang et al. [8] report that an offset smaller than 8 mm is considered pathological, whereas Tannast et al. [9]

alpha angle value above 57° is suggestive of symptomatic FAI type cam.

mention that a distance less than 10 mm is related to FAI.

angle of 47.81° (±5.30°). The relationship between controls and cases is 3:1.

cam increases by 28% compared to having 1° less.

specificity 95.05%, correctly classifying 94% of our sample.

the operated hip was registered.

68 Computed Tomography - Advanced Applications

Texas, USA).

control for each case.

**3.5. Femoral offset**

**Figure 5.** It shows femoral offset measurement. The distance between the anterior margin of the femoral neck and the anterior margin of the femoral head is shown.

### **4. Measurement analysis in CT by image correction in two or three planes**

The multiplanar reconstructions of the 101 asymptomatic individuals included the axial planes to the pelvis and axial slants to the femoral neck. Since the pelvis has a spatial arrangement in three dimensions and considering the deviations by the position of the pelvis in relation to the table of the tomographer, the axial reconstructions and in the three dimensions were corrected in three planes [20, 21], that is to say corrected the rotation, the lateral inclination and the tilting of the pelvis. For the latter, differences between genders were considered, setting a distance of 3 cm between the sacrococcygeal junction and upper border of the pubis in men and 6 cm in women [22]. The evaluation of the images and the measurements were made by radiologists and orthopedic surgeons, using the software Osirix® v4.0.

Our hypothesis is that if acetabular measurements, like Wiberg angle and acetabular version angle, are performed without correction in three planes, the retroversion measures of the pelvis are significantly different, which can lead to misdiagnosis of acetabular overcoverage, meaning pincer-type impingement.

Non-parametric median test was used to compare both groups. A significance level of 0.05 was established and 95% confidence interval was reported. All analyses were performed using Stata v11.2 (StataCorp LP, College Station, Texas, USA).

When analyzing the Wiberg angle, the average value without correction is 38.8° (±7.54), while when correcting in three planes, the average value of the angle increases to 39.4 (±7.59). Although the average difference between the two measurements is 0.6° (±2.9° and range: −6.9–14), this is significant when applying a comparison test for medians (p = 0.01).

Secondly, acetabular retroversion measures were analyzed. Acetabular version angle was measured in six levels of cephalic to caudal, every 3 mm from the upper edge of the acetabular to distal. The sixth measurement coincides with the classic measure of acetabular version, which is performed where the acetabulum is deeper. The measurement was performed as proposed by Kang et al. [8].

The average value of acetabular version angle is shown in **Table 1**. It is evident that the angle value is consistently lower in the measurements made with the pelvis corrected in three planes. The average difference is −07.6° (± 08.0°), this difference being significant (test, p <0.00). The detail of the differences for each level is shown in **Table 1**.

In conclusion, the correction in three planes is important to standardize the measures. Failure to correct the spatial position of the pelvis in the patient overestimates the anteversion and decreases the lateral coverage angle. This is important because it can modify the diagnosis and/or surgical planning.


**Table 1.** It shows median and range of the acetabular version angle by level. Acetabular version angle increased from proximal to distal.

### **5. Measurement analysis related to impingement according to epidemiological variables**

There are physiological differences in the anatomy of the hip according to epidemiological characteristics. It is known that women have greater acetabular anteversion, greater acetabular inclination and greater femoral anteversion. It is therefore presumed that normal values in FAI-related measurements vary between genders [23]. On the other hand, Dudda et al. [24] found that white women had a significantly lower mean alpha angle and a higher average value at the center edge angle as compared to women born in China. This finding suggests that the measures vary between different races, so it is also a variable to consider [24]. Finally, we found a directly proportional increase between the measurement of the acetabular edge center angle and age [25].

In this section, the relationship between three FAI-related variables (acetabular version angle, Wiberg angle and alpha angle) and the epidemiological variables, gender, age, height and weight will be analyzed. A multivariate analysis is applied using Wards's linkage cluster analysis. After clustering, groups will be compared using regression models and non-parametric median test. A significance level of 0.05 was established and 95% confidence interval is reported. All analyses were performed using Stata v11.2 (StataCorp LP, College Station, Texas, USA).

### **5.1. Acetabular version angle**

### *5.1.1. Results*

The average value of acetabular version angle is shown in **Table 1**. It is evident that the angle value is consistently lower in the measurements made with the pelvis corrected in three planes. The average difference is −07.6° (± 08.0°), this difference being significant (test, p <0.00).

In conclusion, the correction in three planes is important to standardize the measures. Failure to correct the spatial position of the pelvis in the patient overestimates the anteversion and decreases the lateral coverage angle. This is important because it can modify the diagnosis

**Level Not corrected Three-plane corrected Average difference** 11.4° (−15.0 to 45.7°) 02.7° (−25.8 to 35.9°) −08.8° (−15.0 to 45.7°) 17.4° (−12.1 to 45.9°) 07.8° (−24.3 to 37.2°) −09.7° (−12.1 to 45.9°) 20.9° (−0.64 to 20.9°) 13.5° (−15.3 to 31.6°) −08.6° (−0.64 to20.9°) 21.2° ( 00.1 to 38.0°) 15.2° (−12.8 to 31.3°) −06.4° (00.1 to38.0°) 20.7° ( 30.9 to 35.5°) 15.8° (−06.9 to 30.7°) −05.0° (30.9 to 35.5°) 20.0° ( 05.6 to 34.8°) 15.5° ( 00.8 to 30.1°) −04.1° (05.6 to 34.8°)

**5. Measurement analysis related to impingement according to** 

There are physiological differences in the anatomy of the hip according to epidemiological characteristics. It is known that women have greater acetabular anteversion, greater acetabular inclination and greater femoral anteversion. It is therefore presumed that normal values in FAI-related measurements vary between genders [23]. On the other hand, Dudda et al. [24] found that white women had a significantly lower mean alpha angle and a higher average value at the center edge angle as compared to women born in China. This finding suggests that the measures vary between different races, so it is also a variable to consider [24]. Finally, we found a directly proportional increase between the measurement of the acetabular edge

**Table 1.** It shows median and range of the acetabular version angle by level. Acetabular version angle increased from

In this section, the relationship between three FAI-related variables (acetabular version angle, Wiberg angle and alpha angle) and the epidemiological variables, gender, age, height and weight will be analyzed. A multivariate analysis is applied using Wards's linkage cluster analysis. After clustering, groups will be compared using regression models and non-parametric median test. A significance level of 0.05 was established and 95% confidence interval is reported. All analyses

were performed using Stata v11.2 (StataCorp LP, College Station, Texas, USA).

The detail of the differences for each level is shown in **Table 1**.

and/or surgical planning.

70 Computed Tomography - Advanced Applications

**epidemiological variables**

proximal to distal.

Three-plane corrected CT shows lower angle value in each level.

center angle and age [25].

The variables used in this analysis are the acetabular version angles measured from level one to six bilateral in the three-plane correction.

Ninety-nine patients were included. Cluster analysis separated two groups of patients (see **Figure 6**). In group 2, 19 patients were assigned; this group presented lower values of acetabular version (acetabulum plus retroversion) with statistical significance in the 14 measured levels (see **Table 2**).

When observing the epidemiological variables, group 2 presents an average age lower than group 1, which is statistically significant and with high power (α = 0.02 and 1-β = 0.86). The age distribution by the group is shown in **Figure 7**. The differences in weight (α = 0.03 and 1-β = 0.59) and height (α = 0.05, 1-β = 0.64) are statistically significant but the power is moderate. Differences in BMI were not significant (α = 0.13 and 1-β = 0.35). Regarding gender, it is observed that there are more women in group 2, this association being significant (α = 0.01 and 1-β = 0.74) (see **Tables 3** and **4**).

When estimating a multivariate logistic regression model with the variables age and sex as independent variables, age has an OR of 1.06 [1.01–1.11] (goodness of fit test = 0.62) and being male has an OR of 4.80 [1.58–14.64] to belong to group 1. The area under the ROC curve is of 0.76 [0.63–0.89].

When estimating a logistic regression model using age as an independent variable, we obtain an OR of 1.06 [1.01–1.11]. The area under the curve is 0.68 [0.55–0.80]. The cut value that maximizes sensitivity and specificity is 34 years, being 58.75 and 73.68%, respectively, correctly

**Figure 6.** A dendrogram showing cluster analysis of acetabular version angle, and two groups are identified.


The probability obtained in the test of median comparison is shown in the last column, and at each level the differences reach statistical significance. R= right, L = left, 3p = 3-plane corrected CT and L = level.

**Table 2.** It shows the mean and standard deviation of acetabular version angle by the group that results from the cluster analysis.

**Figure 7.** It shows age distribution among both groups resulting from cluster analysis of the acetabular version angle.

#### Computed Tomography: Role in Femoroacetabular Impingement http://dx.doi.org/10.5772/intechopen.68558 73


**Table 3.** It shows mean and standard deviation of epidemiological variables by the group that results from the cluster analysis of acetabular version angle.


**Table 4.** It shows gender distribution among both groups that results from the cluster analysis of acetabular version angle .

classifying 70.31% of the sample. In the case of 40 years, the sensitivity decreases to 54.05% and the specificity increases to 77.78%, so having 40 years or more gives you an OR of 6.28 [1.36–29.04] belonging in group 1.

In the estimation of a multinomial regression model, it was observed that the relative risk of having a unilateral positive crossover sign given that the individual belongs to group 2 is 1.05 [0.11–9.72] and bilateral is 7.13 [2.32–21.90].

When estimating a multivariate logistic regression model, including the dichotomized age of 40 years and the presence of a sign of crossover (positive, unilateral and bilateral), it appears that being under 40 years old has an OR of 4.90 [1.02–23.68] and the sign of positive crossover has an OR of 2.40 [1.34–4.30] belonging in group 2. This model presents an area under the curve of 0.77 [0.67–0.87].

#### *5.1.2. Discussion*

**Figure 7.** It shows age distribution among both groups resulting from cluster analysis of the acetabular version angle.

The probability obtained in the test of median comparison is shown in the last column, and at each level the differences

**Table 2.** It shows the mean and standard deviation of acetabular version angle by the group that results from the cluster

reach statistical significance. R= right, L = left, 3p = 3-plane corrected CT and L = level.

analysis.

**Variable Group 1 Group 2 Total P N** 80 (80.81%) 19 (19.19%) 99 0.00 **VERSION 3P L1 R.** 5.80(±9.26) −11.48(±4.80) 2.48(±10.96) 0.00 **VERSION 3P L1 L.** 7.17(±9.74) −14.22(±5.58) 3.06(±12.40) 0.00 **VERSION 3P L2 R.** 10.25(±8.02) −6.98(±4.97) 6.94(±10.14) 0.00 **VERSION 3P L2 L.** 10.78(±8.49) −8.68(±5.60) 7.04(±11.10) 0.00 **VERSION 3P L3 R.** 14.72(±7.58) −1.39(±6.00) 11.62(±9.67) 0.00 **VERSION 3P L3 L.** 15.26(±6.77) −3.48(±6.36) 11.66(±9.97) 0.00 **VERSION 3P L4 R.** 16.76(±6.11) 3.05(±6.08) 14.13(±8.14) 0.00 **VERSION 3P L4 L.** 17.30(±4.96) 1.9(±7.09) 14.34(±8.14) 0.00 **VERSION 3P L5 R.** 17.29(±5.26) 8.12(±4.49) 15.53(±6.26) 0.00 **VERSION 3P L5 L.** 17.67(±4.33) 7.74(±3.57) 15.77(±5.73) 0.00 **VERSION 3P L6 R.** 17.08(±4.87) 9.58(±3.88) 15.64(±5.54) 0.00 **VERSION 3P L6 L.** 17.43(±4.10) 9.99(±3.26) 16.00(±4.92) 0.00 **VERSION 3P L7 R.** 16.80(±5.16) 10.51(±3.38) 15.59(±5.46) 0.00 **VERSION 3P L7 L.** 17.04(±4.05) 10.51(±3.42) 15.78(±4.69) 0.00

72 Computed Tomography - Advanced Applications

In the acetabular version, it was observed that group 1 consistently presented in each level measured medians of angle in a more forward position than group 2. Group 2 presented an average age significantly lower than group 1 and with high statistical power. This suggests that the acetabular orientation varies with age. The calculated OR shows that for each year you grow older, there is a 6% chance of belonging to the group with more predatory acetabulum. Interestingly, the cut point was found at age 34, since the disease is generally described in women who are about 40 years old; therefore, it is possible that the acetabulum that remained retroverted after the age of 30 years is the one that eventually causes the symptomatology.

Likewise, the resulting groups differ in the proportion of individuals by gender, with the number of men in group 1 being more significant, with statistical significance and high power. This suggests that there are differences in acetabular orientation by gender. The individuals included in group 1 are in greater proportion in men, that is to say, male individuals have more anteverse acetabulum than women, which agrees with the literature described for FAI, where the majority of the patients with pincer impingement are women [9, 26].

Ito et al. [27] reports in a cross-sectional study that there is no difference in the version angle regarding age or sex. The number of individuals recruited for the study was 24 symptomatic and 24 healthy. The comparison was performed by ANOVA test, grouping sex and age dichotomized at 40 years old. The difference of their results with respect to this report may be due to the size of the sample used since each group studied contains a maximum of eight individuals.

On the other hand, the estimation of the multinomial regression model shows that there is an association between the clusters formed and the presence of crossover sign. Thus, belonging to group 2 (retroverted acetabulum) increases the relative risk for the presence of both bilateral and unilateral positive crossover sign. This finding suggests that there may be "physiological" crossover at an early age so it is not always pathological. Thus, the development of the pathology will depend on the load applied by each individual in this overcoverage and on how it evolves as it reaches the age, that is, if the acetabulum is oriented anteriorly.

### **5.2. Wiberg angle**

### *5.2.1. Results*

The variables used in this analysis are the Wiberg angle measured in coronal CT in bilateral form and corrected in three planes.

The result of the analysis is presented in the dendrogram (see **Figure 8**), where the presence of two groups with greater distances is observed. When creating these two groups, it is observed that group 1 has average values of acetabular version angle significantly larger than group 2 (see **Table 5**).

When observing the epidemiological variables, it is observed that group 2 presents an average age lower than group 1; this finding is significant and has a high power (α = 0.00 and 1-β = 0.99). The distribution of age is shown in **Figure 9**. The differences found in weight and BMI are also significant however the power is moderate, with α = 0.05 1-β = 0.52 and α = 0.02 and β = 0.64, respectively. Finally, the differences found in size are not statistically significant (α = 0.52, β = 0.09); the same occurs with the higher proportion of males in group 1 (α = 0.99, β = 0.09) (see **Tables 6** and **7**).

When estimating a logistic regression model, age has an OR of 1.08 [1.04–1.12] (goodness of fit test = 0.30) belonging to group 1, with an area under the ROC curve of 0.74 [0.64–0.84]. The cut value that maximizes sensitivity and specificity is 38 years, being 64.58 and 83.02%,

**Figure 8.** A dendrogram showing cluster analysis of Wiberg angle, and two groups are identified.

respectively, correctly ranking 74.26% of the sample. In the case of the 40 years, the sensitivity remains at 60.42% and the specificity decreases to 83.02%, whereby being 40 years or older has an OR of 7.46 [2.97–18.75] belonging to group 1.

#### *5.2.2. Discussion*

Likewise, the resulting groups differ in the proportion of individuals by gender, with the number of men in group 1 being more significant, with statistical significance and high power. This suggests that there are differences in acetabular orientation by gender. The individuals included in group 1 are in greater proportion in men, that is to say, male individuals have more anteverse acetabulum than women, which agrees with the literature described for FAI, where the majority of the patients with pincer impingement are women

Ito et al. [27] reports in a cross-sectional study that there is no difference in the version angle regarding age or sex. The number of individuals recruited for the study was 24 symptomatic and 24 healthy. The comparison was performed by ANOVA test, grouping sex and age dichotomized at 40 years old. The difference of their results with respect to this report may be due to the size of the sample used since each group studied contains a maximum of eight

On the other hand, the estimation of the multinomial regression model shows that there is an association between the clusters formed and the presence of crossover sign. Thus, belonging to group 2 (retroverted acetabulum) increases the relative risk for the presence of both bilateral and unilateral positive crossover sign. This finding suggests that there may be "physiological" crossover at an early age so it is not always pathological. Thus, the development of the pathology will depend on the load applied by each individual in this overcoverage and on how it evolves as it

The variables used in this analysis are the Wiberg angle measured in coronal CT in bilateral

The result of the analysis is presented in the dendrogram (see **Figure 8**), where the presence of two groups with greater distances is observed. When creating these two groups, it is observed that group 1 has average values of acetabular version angle significantly larger than group 2

When observing the epidemiological variables, it is observed that group 2 presents an average age lower than group 1; this finding is significant and has a high power (α = 0.00 and 1-β = 0.99). The distribution of age is shown in **Figure 9**. The differences found in weight and BMI are also significant however the power is moderate, with α = 0.05 1-β = 0.52 and α = 0.02 and β = 0.64, respectively. Finally, the differences found in size are not statistically significant (α = 0.52, β = 0.09); the same occurs with the higher proportion of males in group 1 (α = 0.99,

When estimating a logistic regression model, age has an OR of 1.08 [1.04–1.12] (goodness of fit test = 0.30) belonging to group 1, with an area under the ROC curve of 0.74 [0.64–0.84]. The cut value that maximizes sensitivity and specificity is 38 years, being 64.58 and 83.02%,

reaches the age, that is, if the acetabulum is oriented anteriorly.

[9, 26].

individuals.

**5.2. Wiberg angle**

form and corrected in three planes.

74 Computed Tomography - Advanced Applications

β = 0.09) (see **Tables 6** and **7**).

*5.2.1. Results*

(see **Table 5**).

In the conglomerate analysis of the Wiberg angle, a correlation with age is also observed, showing that as the age increases the average value of the Wiberg angle does as well. For each completed year, the probability of belonging to the group with higher Wiberg angle increases by 6%. The cut value found is 6 years longer than in the case of the acetabular version angle,


The probability obtained in the test of median comparison is shown in the last column, and at each level the differences reach statistical significance. R = right, L = left and 3-p = 3-plane corrected.

**Table 5.** It shows mean and standard deviation of Wiberg angle by the group that results from the cluster analysis.

**Figure 9.** It shows age distribution among both groups, resulting from cluster analysis of Wiberg angle.


**Table 6.** It shows mean and standard deviation of epidemiological variables by the group that results from the cluster analysis of Wiberg angle.


**Table 7.** It shows gender distribution among both groups that result from the cluster analysis of Wiberg angle.

which implies that the acetabular coverage increases later. This finding is consistent with what was described by Konishi et al. [28], where it is mentioned that the angle increases with age.

#### **5.3. Alpha angle**

#### *5.3.1. Results*

which implies that the acetabular coverage increases later. This finding is consistent with what was described by Konishi et al. [28], where it is mentioned that the angle increases with age.

**Table 6.** It shows mean and standard deviation of epidemiological variables by the group that results from the cluster

**Table 7.** It shows gender distribution among both groups that result from the cluster analysis of Wiberg angle.

**Figure 9.** It shows age distribution among both groups, resulting from cluster analysis of Wiberg angle.

**Age** 43.54 (±15.81) 30.74 (±9.76) 36.82 (±14.43) **Weight (kg)** 74.23 (±13.14) 69.09 (±12.58) 71.56 (±13.04) **Height (mts)** 1.68 (±0.09) 1.67 (±0.08) 1.68 (±0.09) **BMI** 26.14 (±3.36) 24.63 (±3.20) 25.35 (±3.35)

**Group 1 Group 2 Total**

**Wiberg cluster Female Male 1** 19 (39.58%) 29 (60.42%) **2** 22 (41.51%) 31 (58.49%) **TOTAL** 41 (40.69%) 60 (59.41%)

BMI = body mass index, kg = kilograms and mts = meters.

76 Computed Tomography - Advanced Applications

analysis of Wiberg angle.

The variables used in this analysis correspond to alpha femoral angle measurements. In an axial oblique cut of the femoral neck, it was divided into thirds from chepalic to caudal. The measurement was made at the second third in the anterosuperior region, that is to say, using the clock handle form, from 1:00 to 3:00. This measurement was made in both hips.

Hundred patients were included. Cluster analysis separated two groups of patients. In group 2, 13 patients were assigned, which presented higher alpha angle values with statistical significance in 16 of the 18 measurement levels analyzed (see **Table 8**). The result of the analysis is presented in the dendrogram (**Figure 10**), where we observe the presence of two groups that have greater distances.


The probability obtained in the test of median comparison is shown in the last column, and at each level the differences reach statistical significance. R = right and L = left.

**Table 8.** It shows mean and standard deviation of alpha angle by a group that results from the cluster analysis.

**Figure 10.** A dendrogram showing cluster analysis of femoral alpha angle, and two groups are identified.

In the measurements of the alpha angle by levels, the difference was significantly greater in group 2 in levels 1 and 2 bilaterally. However, although the average value in group 2 was higher, the difference in level 3 was not significant, either to the right or to the left. In the measurements of the alpha angle by radians, the difference in all hourly radii was significant bilaterally, the average being consistently higher in group 2.

Observing the epidemiological variables, it is observed that group 2 has a higher average age, but the difference is not significant (α = 0.22, 1-β = 0.44). The differences in size, weight and BMI are minimal and therefore are not statistically significant [(height, α = 0.36, 1-β = 0.46), weight, α = 0.19, 1-β = 0.52 and BMI, α = 0.29; 1-β = 0.99)]. The distributions of these variables by groups can be observed in graphs 17, 18, 19 and 20. As for gender, it is observed that in


**Table 9.** It shows mean and standard deviation of epidemiological variables by a group that results from the cluster analysis of Wiberg angle.


**Table 10.** It shows gender distribution among both groups that result from the cluster analysis of the alpha angle.

group 2, there is a greater proportion of men than in group 1, however, this is not significant (p = 0.07) (see **Tables 9** and **10**).

#### *5.3.2. Discussion*

The variables measured in the femur are not related to the epidemiological variables analyzed: age, gender, height, weight and body mass index, which is consistent with the literature reviewed [29, 30].

### **6. Conclusions**

In the measurements of the alpha angle by levels, the difference was significantly greater in group 2 in levels 1 and 2 bilaterally. However, although the average value in group 2 was higher, the difference in level 3 was not significant, either to the right or to the left. In the measurements of the alpha angle by radians, the difference in all hourly radii was significant

**Figure 10.** A dendrogram showing cluster analysis of femoral alpha angle, and two groups are identified.

Observing the epidemiological variables, it is observed that group 2 has a higher average age, but the difference is not significant (α = 0.22, 1-β = 0.44). The differences in size, weight and BMI are minimal and therefore are not statistically significant [(height, α = 0.36, 1-β = 0.46), weight, α = 0.19, 1-β = 0.52 and BMI, α = 0.29; 1-β = 0.99)]. The distributions of these variables by groups can be observed in graphs 17, 18, 19 and 20. As for gender, it is observed that in

**Group 1 Group 2 Total**

**Table 9.** It shows mean and standard deviation of epidemiological variables by a group that results from the cluster

**Age** 36.40 (±14.89) 40.15 (±11.33) 36.89 (±14.49) **Weight (kg)** 70.87 (±13.42) 75.00 (±09.72) 71.41 (±13.03) **Height (Mts)** 1.67 (±0.09) 1.70 (±0.10) 1.67 (±0.09) **BMI** 25.23 (±3.51) 25.98 (±2.06) 25.33 (±3.36)

bilaterally, the average being consistently higher in group 2.

78 Computed Tomography - Advanced Applications

BMI = body mass index, Kg = kilograms and mts = meters.

analysis of Wiberg angle.


### **Author details**

Maximiliano Barahona\*, Jaime Hinzpeter and Cristian Barrientos

\*Address all correspondence to: maxbarahonavasquez@gmail.com

Orthopedic Surgery Department, Hospital Clinico Universidad de Chile, Chile

### **References**


[14] Barrientos C, Diaz J, Brañes J, Chaparro F, Barahona M, Salazar A, Hinzpeter J. Hip morphology characterization: Implications in femoroacetabular impingement in a Chilean population. Orthopaedic Journal of Sports Medicine. 2014;**2**(10):2325967114552800

**References**

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of Radiology. 2007;**63**(1):29-35

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[1] Canham CD, Domb BG, Giordano BD. Atraumatic hip instability. JBJS Reviews. 2016;**4**(5):e3 [2] Lee A, Emmett L, Van der Wall H, Kannangara S, Mansberg R, Fogelman I. SPECT/CT of

[3] Ganz R, Parvizi J, Beck M, Leunig M, Nötzli H, Siebenrock KA. Femoroacetabular impingement: A cause for osteoarthritis of the hip. Clinical Orthopaedics and Related

[4] Beaulé P, Zaragoza E, Motamedi K, Copelan N, Dorey F. Three-dimensional computed tomography of the hip in the assessment of femoroacetabular impingement. Journal of

[5] Hinzpeter J, Barrientos C, Barahona M, Diaz J, Zamorano A, Salazar A, Catalan J. Fluid extravasation related to hip arthroscopy: A prospective computed tomography-based

[6] Kassarjian A, Brisson M, Palmer WE. Femoroacetabular impingement. European Journal

[7] Beall DP, Sweet CF, Martin HD, Lastine CL, Grayson DE, Ly JQ, et al. Imaging findings of femoroacetabular impingement syndrome. Skeletal Radiology. 2005;**34**(11):691-701

[8] Kang AC, Gooding AJ, Coates MH, Goh TD, Armour P, Rietveld J. Computed tomography assessment of hip joints in asymptomatic individuals in relation to femoroacetabular impingement. The American Journal of Sports Medicine. 2010;**38**(6):1160-1165

[9] Tannast M, Siebenrock KA, Anderson SE. Femoroacetabular impingement: Radiographic diagnosis—What the radiologist should know. American Journal of Radiology. 2007;**188**(6):

[10] Barton C, Salineros MJ, Rakhra KS, Beaulé PE. Validity of the alpha angle measurement on plain radiographs in the evaluation of cam-type femoroacetabular impingement.

[11] Notzli HP, Wyss TF, Stoecklin CH, Schmid MR, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. The

[12] Hack K, Di Primio G, Rakhra K, Beaulé PE. Prevalence of cam-type femoroacetabular impingement morphology in asymptomatic volunteers. The Journal of Bone and Joint

[13] Allen D, Beaulé PE, Ramadan O, Doucette S. Prevalence of associated deformities and hip pain in patients with cam-type femoroacetabular impingement. The Journal of Bone

Clinical Orthopaedics and Related Research. 2011;**469**(2):464-469

and Joint Surgery. British Volume. 2009;**91**(5):589-594

Journal of Bone and Joint Surgery. British Volume. 2002;**84**(4):556-560

study. Orthopaedic Journal of Sports Medicine. 2015;**3**(3):2325967115573222

femeroacetabular impingement. Clinical Nuclear Medicine. 2008;**33**(11):757


## **OncoSpineSeg: A Software Tool for a Manual Segmentation of Computed Tomography of the Spine on Cancer Patients**

Silvia Ruiz-España and David Moratal

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68552

### **Abstract**

[28] Konishi N, Mieno T. Determination of acetabular coverage of the femoral head with use of a single anteroposterior radiograph. The Journal of Bone and Joint Surgery. American

[29] Toogood PA, Skalak A, Cooperman DR. Proximal femoral anatomy in the normal human

[30] Gosvig KK, Jacobsen S, Palm H, Sonne-Holm S, Magnusson E. A new radiological index for assessing asphericity of the femoral head in cam impingement. Journal of Bone and

population. Clinical Orthopaedics and Related Research. 2009;**467**(4):876

Joint Surgery. British Volume. 2007;**89**(10):1309-1316

Volume. 1993;**75**:1318-1333

82 Computed Tomography - Advanced Applications

The organ most commonly affected by metastatic cancer is the skeleton, and spine is the site where it causes the highest morbidity. Computer-aided diagnosis (CAD) for detecting and assessing metastatic disease in bone or other spine disorders can assist physicians to perform their decision-making tasks. A precise segmentation of the spine is important as a first stage in any automatic diagnosis task. However, it is a challenging problem to segment correctly an affected spine, and it is a crucial step to assess quantitatively the results of segmentation by comparing them with the results of a manual segmentation, reviewed by one experienced radiologist. This chapter presents the design of a MATLAB-based software for the manual segmentation of the spine. The software tool has a simple and easy to use interface, and it works with either computed tomography or magnetic resonance imaging (MRI). A typical workflow includes loading the image volume, creating multi-planar reconstructions, manually contouring the vertebrae, spinal lesions, intervertebral discs and spinal canal with availability of different segmentation tools, classification of the bone into healthy bone, osteolytic metastases, osteoblastic metastases or mixed lesions, being also possible to classify an object as a false-positive and a 3D reconstruction of the segmented objects.

**Keywords:** computed tomography, magnetic resonance imaging, manual segmentation, metastatic disease, spinal canal, intervertebral discs, vertebrae

### **1. Introduction**

Spine is a structure commonly involved in several prevalent diseases causing, in most of the cases, back pain [1]. Back pain is an important public health problem in industrialized countries [1], and it is a common cause of disability, activity limitation, work absenteeism and economic burden [2].

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Moreover, spinal metastases affect many patients with advanced cancer since the bone is the most common spot of metastatic recurrence and the spine the most frequent place of bone metastases [3]. Bone metastasis is typically referred as osteolytic or osteoblastic. Osteolytic or lytic lesions are associated with bone resorption; there is a scarce new bone formation and focal bone destruction. Osteoblastic or blastic lesions are associated with an increased osteoblastic activity; these lesions seem to have little or no resorptive component. The structure of the new bone grows abnormally and causes the bone to be weak [4]. Metastatic spine is prone to several complications such as fractures and spinal cord compression due to weakness [4, 5].

Nowadays, spinal imaging studies are increasing worldwide [6], and computer-aided diagnosis (CAD) is beginning to be a part of the routine clinical work, being applied in the detection and differential diagnosis of abnormalities. Hence, its demand over the past decade has increased as a way to assist radiologists in the imaging diagnosis of back pain [7, 8]. Automatic reliable methods to quantify and classify spinal disorders, and an early detection of metastatic disease to prevent complications, are an unmet need. However, an accurate segmentation of the spine is an essential step prior to any diagnosis task. For this reason, considerable research effort has been directed towards the development of automatic or semi-automatic algorithms for the segmentation of the spine in computed tomography (CT) or magnetic resonance imaging (MRI) [9]. There are methods that do not include prior information in the process of segmentation as this kind of data is not always available. These algorithms mainly rely on the information extracted from the acquired images, for example, the application of intensity thresholds, watershed, level-set and direct graph methods [10–13]. However, other methods incorporate higher-level knowledge of the object of interest to facilitate or improve the segmentation results. Most of them are based on deformable models [14–17]. For example, using an active shape model, a statistical representation of the object is performed. The active shape model is used to identify objects, within other images, considered as the same class by using landmark points [18, 19]. Some algorithms also integrate image patches, such as intensity or texture, into the statistical model. These methods are known as active appearance models [20]. Using an atlas-based segmentation is also a way to introduce anatomical information related to the position of an organ [21–23]. The raw data values that are stored in an image are not always sufficiently informative, especially in the case of organs whose limit surface is not clearly defined in terms of signal value. In these cases, the only way to classify appropriately a voxel is taking into account its spatial location, either in absolute co-ordinates or, more commonly, given its spatial relationship with other already segmented structures. This is exactly the kind of information that can be provided by an atlas.

Unfortunately, the segmentation process involves four image-related problems. They are partial volume effect, intensity inhomogeneity, intensity similarity and noise. These problems and the differences in body structures among individuals make the segmentation process a very challenging task. Therefore, in order to obtain an accurate and robust segmentation, it is a crucial step to assess quantitatively the results of segmentation by comparing them with the results of a manual segmentation, made by experts. Some free softwares developed for image analysis or as automatic (semi-automatic) medical image segmentation tools can be also used for manual segmentation. For instance, Heilberg et al. developed a cardiovascular image analysis software package called segment. The main features of this software include loading Digital Imaging and Communications in Medicine (DICOM) images from all major MRI vendors, display of multiple image stacks at the same time, automated segmentation of the left ventricle, flow quantification, region of interest analysis, myocardial viability analysis and image fusion tools. The software also incorporates all the necessary tools to perform a manual segmentation [24]. Casero et al. developed a new spline tool for the open source software platform Seg3D [25] in order to perform the manual segmentation of the annulus of the cardiac valves. In this work, they review two manual segmentation approaches, slice-byslice and manual segmentation interpolating a sparse set of landmarks [26]. However, these softwares are mainly focused on cardiovascular image analysis.

Moreover, spinal metastases affect many patients with advanced cancer since the bone is the most common spot of metastatic recurrence and the spine the most frequent place of bone metastases [3]. Bone metastasis is typically referred as osteolytic or osteoblastic. Osteolytic or lytic lesions are associated with bone resorption; there is a scarce new bone formation and focal bone destruction. Osteoblastic or blastic lesions are associated with an increased osteoblastic activity; these lesions seem to have little or no resorptive component. The structure of the new bone grows abnormally and causes the bone to be weak [4]. Metastatic spine is prone to several complications such as fractures and spinal cord compres-

Nowadays, spinal imaging studies are increasing worldwide [6], and computer-aided diagnosis (CAD) is beginning to be a part of the routine clinical work, being applied in the detection and differential diagnosis of abnormalities. Hence, its demand over the past decade has increased as a way to assist radiologists in the imaging diagnosis of back pain [7, 8]. Automatic reliable methods to quantify and classify spinal disorders, and an early detection of metastatic disease to prevent complications, are an unmet need. However, an accurate segmentation of the spine is an essential step prior to any diagnosis task. For this reason, considerable research effort has been directed towards the development of automatic or semi-automatic algorithms for the segmentation of the spine in computed tomography (CT) or magnetic resonance imaging (MRI) [9]. There are methods that do not include prior information in the process of segmentation as this kind of data is not always available. These algorithms mainly rely on the information extracted from the acquired images, for example, the application of intensity thresholds, watershed, level-set and direct graph methods [10–13]. However, other methods incorporate higher-level knowledge of the object of interest to facilitate or improve the segmentation results. Most of them are based on deformable models [14–17]. For example, using an active shape model, a statistical representation of the object is performed. The active shape model is used to identify objects, within other images, considered as the same class by using landmark points [18, 19]. Some algorithms also integrate image patches, such as intensity or texture, into the statistical model. These methods are known as active appearance models [20]. Using an atlas-based segmentation is also a way to introduce anatomical information related to the position of an organ [21–23]. The raw data values that are stored in an image are not always sufficiently informative, especially in the case of organs whose limit surface is not clearly defined in terms of signal value. In these cases, the only way to classify appropriately a voxel is taking into account its spatial location, either in absolute co-ordinates or, more commonly, given its spatial relationship with other already segmented structures. This is

exactly the kind of information that can be provided by an atlas.

Unfortunately, the segmentation process involves four image-related problems. They are partial volume effect, intensity inhomogeneity, intensity similarity and noise. These problems and the differences in body structures among individuals make the segmentation process a very challenging task. Therefore, in order to obtain an accurate and robust segmentation, it is a crucial step to assess quantitatively the results of segmentation by comparing them with the results of a manual segmentation, made by experts. Some free softwares developed for

sion due to weakness [4, 5].

84 Computed Tomography - Advanced Applications

In this chapter, we present a software tool for performing the manual segmentation of vertebrae, intervertebral discs, spinal metastases and spinal canal. To the best of our knowledge, there is no free software for the manual segmentation of the spine. For this reason, it has been designed to get references with which users can compare automatic segmentations. The software tool can be divided into six main modules, and a general approach is shown in **Figure 1**.

**Figure 1.** General approach of the manual segmentation software developed. After loading a 3D image volume, a multi-planar reconstruction from the original axial planes is performed. Next, it is necessary to label the structure to be segmented. Segmentation can be performed in any of the three views and in two different ways. Following segmentation, it is possible to classify the segmented bone. Finally, a 3D reconstruction can be obtained.

### **2. Software description**

#### **2.1. Software platform and data**

The software tool presented in this work is called OncoSpineSeg, and its main interface is shown in **Figure 2**. The graphical user interface and all the implemented functions have been developed under MATLAB 7.10 (R2010a) (The Mathworks, Inc., Natick, MA, USA). Using MATLAB, the code can be written in a straightforward manner, which allows easily modifying, extending or integrating new functions. It can be executed under Windows, Linux or Mac OS.

The software has been tested with CT imaging and also with MRI. Both modalities are widely used for the diagnosis of spinal disorders. MRI is the preferred modality for the diagnosis of intervertebral disc pathology and spinal stenosis because it provides better contrast resolution to differentiate soft tissues [27, 28]. However, bony structures are more clearly identified in CT scans being possible to distinguish between cortical and trabecular bones and allowing accurate diagnosis of vertebral lesions [29].

The software supports the classical formats encountered in medical applications, e.g. DICOM, Neuroimaging Informatics Technology Initiative (Nifti), Raw, Meta-Image or the Visualization Toolkit (VTK). When 3D data are loaded, relevant information such as image data, resolution, acquisition details or patient identification is stored as a structure to be included in the final segmentation output file. The final output file will also contain the manual segmentation.

**Figure 2.** Main interface of OncoSpineSeg. (a) To load the 3D data volume, a saved segmentation, or to perform a 3D reconstruction. (b) To prepare images for segmentation and to perform manual segmentation. (c) To get information about the objects, which have been already segmented. (d) To copy and paste different objects and to edit the contour or label of a segmented object. (e) Multi-planar reconstruction. The straight vertical and horizontal lines are the position markers. (f) To label the structure to be segmented. (g) To classify the segmented bone ('textures' menu). There are three different options for the representation of the segmented objects, and there is information about the texture patterns associated with the different bone types available in the 'textures' menu.

After loading a 3D image volume, a multi-planar reconstruction (MPR) is performed. Sagittal and coronal cross sections are reconstructed from original axial planes. In this way, it allows an easy and a fast mutual cross-correlation of any object with the other views. The software has available position markers that allow the user to move through the volume data only by clicking with the mouse button at the desired position over any of the three planes. It is also possible scrolling between image slices using a set of sliders.

The software tool allows loading a second dataset. That is, it is also possible to load a saved segmentation in order to easily fix mistakes, using the editing tool, or finish an incomplete segmentation. This will be explained in Section 2.3.

### **2.2. Tools for image segmentation preparation**

**2. Software description**

ual segmentation.

**2.1. Software platform and data**

86 Computed Tomography - Advanced Applications

The software tool presented in this work is called OncoSpineSeg, and its main interface is shown in **Figure 2**. The graphical user interface and all the implemented functions have been developed under MATLAB 7.10 (R2010a) (The Mathworks, Inc., Natick, MA, USA). Using MATLAB, the code can be written in a straightforward manner, which allows easily modifying, extending or integrating new functions. It can be executed under Windows, Linux or Mac OS. The software has been tested with CT imaging and also with MRI. Both modalities are widely used for the diagnosis of spinal disorders. MRI is the preferred modality for the diagnosis of intervertebral disc pathology and spinal stenosis because it provides better contrast resolution to differentiate soft tissues [27, 28]. However, bony structures are more clearly identified in CT scans being possible to distinguish between cortical and trabecular

The software supports the classical formats encountered in medical applications, e.g. DICOM, Neuroimaging Informatics Technology Initiative (Nifti), Raw, Meta-Image or the Visualization Toolkit (VTK). When 3D data are loaded, relevant information such as image data, resolution, acquisition details or patient identification is stored as a structure to be included in the final segmentation output file. The final output file will also contain the man-

**Figure 2.** Main interface of OncoSpineSeg. (a) To load the 3D data volume, a saved segmentation, or to perform a 3D reconstruction. (b) To prepare images for segmentation and to perform manual segmentation. (c) To get information about the objects, which have been already segmented. (d) To copy and paste different objects and to edit the contour or label of a segmented object. (e) Multi-planar reconstruction. The straight vertical and horizontal lines are the position markers. (f) To label the structure to be segmented. (g) To classify the segmented bone ('textures' menu). There are three different options for the representation of the segmented objects, and there is information about the texture patterns

bones and allowing accurate diagnosis of vertebral lesions [29].

associated with the different bone types available in the 'textures' menu.

In spite of high contrast of MRI and CT images, there are often unclear object boundaries or similar structures in close vicinity, which impede obtaining an exact segmentation.

Classic image processing tools have been developed to facilitate manual segmentation. By using these tools, it is possible to adjust image details such as contrast and brightness or to zoom into specific regions of the image, according to mouse movements. Zoom is applied to all sections, axial, sagittal and coronal, at the same time.

Position markers are also useful for image preparation because they allow users to move between image slices and select the most appropriate region to segment each structure.

### **2.3. Slice-by-slice manual segmentation**

Prior to start manual segmentation, a mandatory first step is to label the structure, which is going to be segmented. If the structure is not labelled, the process of manual segmentation will not be available and the user will receive information about how to proceed. In the presented tool, there is a module for this purpose, which opens up an anatomical image displaying the anterior and lateral views of an artificial spine. Only by clicking on the vertebra, we want segmentation of the specific label to be automatically set. It is also possible to select a label for the intervertebral discs and the spinal canal. A 'NO LABEL' label can also be used, allows segmenting a structure without any specific information. A default colour is assigned to each one of the available labels, although these colours can be changed. Any performed change will be stored and saved with the segmentation results.

There are two ways to manually segment the structures, and, in both cases, it is possible to segment in any of the three views (axial, sagittal and coronal), shown in **Figure 1**. In the first way, the region of interest is specified by placing a set of points using the mouse. Once the regions have been specified, they can interactively be dragged, or resized by deleting or adding new points. Then, the set of points is interpolated with a spline curve. In the second way, the region of interest is manually drawn, as using a pencil. To facilitate the segmentation task, the software permits the user to copy one or several contours and paste them upwards and downwards through the slices. The user has the possibility of using the editing tool, anytime, to edit any contour, as well as its label, to accommodate them to a more precise segmentation or to change its identification. If it is necessary to perform the segmentation again, it is possible to undo the last segmentation or delete all or just some specific contours.

The segmented objects are shown in all three views: axial, sagittal and coronal. In the axial view, it is only possible to see the segmentations performed in the current slice. However, in the sagittal and coronal views, the segmentations performed in all other slices are shown at the level indicated by the markers. An example of slice-by-slice segmentation of the vertebrae and the spinal canal in CT images is shown in **Figure 3**.

**Figure 3.** (a) Manual segmentation of a slice corresponding to the vertebra L3 and to the spinal canal. (b) and (c) show the corresponding slices to the vertebra for the sagittal and coronal views, respectively, as selected by the markers.

Another example of manual segmentation is shown in **Figure 4**. In this case, all intervertebral discs of the lumbar region have been segmented in MRI.

The software offers, constantly, information about the objects segmented in the current slice and the objects already segmented within the whole volume. Mask values and labels are already accessible after segmentation. All masks corresponding to the segmented objects are stored in a volume data. As stated previously, the structure of the final file has different fields for storing important information. Details such as image data, spatial resolution, acquisition details, patient identification and user's name, besides all previously reported segmentation data (masks, labels and colours assigned to each label), will be stored as a .mat.

### **2.4. Bone classification**

segmentation or to change its identification. If it is necessary to perform the segmentation again, it is possible to undo the last segmentation or delete all or just some specific contours. The segmented objects are shown in all three views: axial, sagittal and coronal. In the axial view, it is only possible to see the segmentations performed in the current slice. However, in the sagittal and coronal views, the segmentations performed in all other slices are shown at the level indicated by the markers. An example of slice-by-slice segmentation of the vertebrae

**Figure 3.** (a) Manual segmentation of a slice corresponding to the vertebra L3 and to the spinal canal. (b) and (c) show the corresponding slices to the vertebra for the sagittal and coronal views, respectively, as selected by the markers.

and the spinal canal in CT images is shown in **Figure 3**.

88 Computed Tomography - Advanced Applications

Once the segmentation of the structures has been performed, it is possible to classify the segmented bone. In the right side of the software interface, a menu called 'textures' is available. This menu permits to categorize the bone into healthy bone (default mode), osteolytic metastases, osteoblastic metastases or a mixture of osteolytic and osteoblastic lesions. It is also possible to classify an object as a false-positive (i.e. osteophytes).

According to the selected bone lesion, different texture patterns are applied, as shown in **Figure 5**. In addition, in the right side of the software interface, a panel called 'texture description' can be found where there is information about the textures associated with the different available bone types. In this way, the user can easily differentiate among the different spinal lesions.

There are different ways to visualize the structures, which have been segmented and classified. A menu called 'image representation' is available for this purpose. Inside the menu

**Figure 4.** (a) Manual segmentation of a slice corresponding to the intervertebral disc L5-S1 in the axial view of an MR image. (b) Shows the segmentation of all lumbar intervertebral discs in the sagittal view. External contours are shown with a solid line.

**Figure 5.** (a) Manual segmentation of a slice corresponding to the vertebra L4 and to the spinal canal. The striped region corresponds to an osteolytic metastasis. The segmentation of all the slices corresponding to the vertebra L4 is shown in the point indicated by the markers, in sagittal section (b) and coronal section (c).

there are three visualization options: selecting 'external contours' allows to show only the segmentation of the spine without any lesion, 'texture contours' permits us to visualize the segmentation contour of the spine and all the spinal lesions and, finally, 'solid objects' allows to depict segmentation of the spine and the spinal lesions with their corresponding texture patterns.

At this point, a complete spine segmentation has been performed, and it can be used as a reference to assess the accuracy of automatic segmentation methods, or to evaluate metastatic involvement.

#### **2.5. 3D reconstruction**

there are three visualization options: selecting 'external contours' allows to show only the segmentation of the spine without any lesion, 'texture contours' permits us to visualize the segmentation contour of the spine and all the spinal lesions and, finally, 'solid objects' allows to depict segmentation of the spine and the spinal lesions with their corresponding texture

**Figure 5.** (a) Manual segmentation of a slice corresponding to the vertebra L4 and to the spinal canal. The striped region corresponds to an osteolytic metastasis. The segmentation of all the slices corresponding to the vertebra L4 is shown in

the point indicated by the markers, in sagittal section (b) and coronal section (c).

90 Computed Tomography - Advanced Applications

At this point, a complete spine segmentation has been performed, and it can be used as a reference to assess the accuracy of automatic segmentation methods, or to evaluate metastatic

patterns.

involvement.

3D reconstruction provides accurate information of the 3D structure of the whole spine, which can be very important as some clinical applications often use some parameters obtained from these 3D reconstructions.

The software uses a volume rendering algorithm to reconstruct an isosurface from the volumetric dataset containing the segmentation results. It also smooths the resulting isosurfaces, applies a colour, which corresponds to colours assigned during labelling, and displays the 3D object. The resulting image can be easily rotated, zoomed or saved. An example of a 3D reconstruction is shown in **Figure 6**.

**Figure 6.** (a) 3D reconstruction of a whole spine with a spinal metastasis. The vertebra with the circle is zoomed in (b) and (c) where a metastasis can be distinguished (arrow).

### **3. Conclusions and future work**

A software tool called OncoSpineSeg has been presented. This tool permits to manually segment an MRI or CT dataset, showing vertebral bodies, spinal metastases, intervertebral discs and spinal canal.

OncoSpineSeg has been fully developed using MATLAB in a straightforward manner, which allows the user not only modify or integrate new functions but also easily adapt the software to detect other spinal lesions or segment other structures. All the needed tools to facilitate the workflow have been implemented, such as the contour editing mode to fix mistakes or redraw inaccurate contours without the necessity of drawing again the complete contour. In addition, it offers a simple, intuitive and easy to use interface.

Slice-by-slice segmentation is a time-consuming process. However, it is widely known the importance of having image sets, manually segmented by experts, for reference. For this reason, and in order to facilitate the advance of research on this topic, we expect to share OncoSpineSeg through internet under a free to download open source license. We also expect to provide a database of several spine CT volumes and the manual segmentation of the vertebral bodies and spinal canal. In addition, OncoSpineSeg will be also available in source code to allow modifications and extensions.

### **Acknowledgements**

The authors thank the financial support of the Spanish Ministerio de Economía y Competitividad (MINECO) and the FEDER funds under Grants TEC2012-33778 and BFU2015- 64380-C2-2-R. The authors thank Dr. Estanislao Arana for his collaboration.

### **Author details**

Silvia Ruiz-España and David Moratal\*

\*Address all correspondence to: dmoratal@eln.upv.es

Center for Biomaterials and Tissue Engineering, Universitat Politècnica de València, Valencia, Spain

### **References**


[3] Oliveira MF, Rotta JM, Botelho RV. Survival analysis in patients with metastatic spinal disease: The influence of surgery, histology, clinical and neurologic status. Arquivos de Neuro-Psiquiatria. 2015;**73**(4):330-335. DOI: 10.1590/0004-282X20150003

**3. Conclusions and future work**

92 Computed Tomography - Advanced Applications

code to allow modifications and extensions.

Silvia Ruiz-España and David Moratal\*

\*Address all correspondence to: dmoratal@eln.upv.es

**Acknowledgements**

**Author details**

Spain

**References**

addition, it offers a simple, intuitive and easy to use interface.

discs and spinal canal.

A software tool called OncoSpineSeg has been presented. This tool permits to manually segment an MRI or CT dataset, showing vertebral bodies, spinal metastases, intervertebral

OncoSpineSeg has been fully developed using MATLAB in a straightforward manner, which allows the user not only modify or integrate new functions but also easily adapt the software to detect other spinal lesions or segment other structures. All the needed tools to facilitate the workflow have been implemented, such as the contour editing mode to fix mistakes or redraw inaccurate contours without the necessity of drawing again the complete contour. In

Slice-by-slice segmentation is a time-consuming process. However, it is widely known the importance of having image sets, manually segmented by experts, for reference. For this reason, and in order to facilitate the advance of research on this topic, we expect to share OncoSpineSeg through internet under a free to download open source license. We also expect to provide a database of several spine CT volumes and the manual segmentation of the vertebral bodies and spinal canal. In addition, OncoSpineSeg will be also available in source

The authors thank the financial support of the Spanish Ministerio de Economía y Competitividad (MINECO) and the FEDER funds under Grants TEC2012-33778 and BFU2015-

Center for Biomaterials and Tissue Engineering, Universitat Politècnica de València, Valencia,

[1] Loney PL, Stratford PW. The prevalence of low back pain in adults: A methodological

[2] Hoy D, Brooks P, Blyth F, Buchbinder R. The epidemiology of low back pain. Best Practice and Research Clinical Rheumatology. 2010;**24**(6):769-781. DOI: 10.1016/j.berh.2010.10.002

64380-C2-2-R. The authors thank Dr. Estanislao Arana for his collaboration.

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[27] Brayda-Bruno M, Tibiletti M, Ito K, Fairbank J, Galbusera F, Zerbi A, et al. Advances in the diagnosis of degenerated lumbar discs and their possible clinical application. European Spine Journal. 2014;**23**(3):S315–S323. DOI: 10.1007/s00586-013-2960-9

[16] Klinder T, Ostermann J, Ehm M, Franz A, Kneser R, Lorenz C. Automated model-based vertebra detection, identification, and segmentation in CT images. Medical Image

[17] Korez R, Ibragimov B, Likar B, Pernus F, Vrtovec T. A Framework for automated spine and vertebrae interpolation-based detection and model-based segmentation. IEEE Transactions on Medical Imaging. 2015;**34**(8):1649-1662. DOI: 10.1109/TMI.2015.

[18] Rasoulian A, Rohling R, Abolmaesumi P. Lumbar spine segmentation using a statistical multi-vertebrae anatomical shape+pose model. IEEE Transactions on Medical Imaging.

[19] Castro-mateos I, Pozo JM, Pereañez M, Lekadir K, Lazary A, Frangi AF. Statistical interspace models (SIMs): Application to robust 3D spine segmentation. IEEE Transactions

[20] Roberts MG, Cootes TF, Pacheco E, Oh T, Adams JE. Segmentation of lumbar vertebrae using part-based graphs and active appearance models. In: Proceedings of the Medical Image Computing and Computer-Assisted Intervention (MICCAI 209). 2009;**12**(Pt

[21] Forsberg D. Atlas-based registration for accurate segmentation of thoracic and lumbar vertebrae in CT data. Recent Advances in Computational Methods and Clinical

Applications for Spine Imaging. 2015;**20**:49-59. DOI: 10.1007/978-3-319-14148-0\_5

[22] Hardisty M, Gordon L, Agarwal P, Skrinskas T, Whyne C. Quantitative characterization of metastatic disease in the spine. Part I. Semiautomated segmentation using atlas-based deformable registration and the level set method. Medical Physics. 2007;**34**(8):3127. DOI:

[23] Ruiz-España S, Domingo J, Díaz-Parra A, Dura E, D'Ocón-Alcañiz V, Arana E, et al. Automatic segmentation of the spine by means of a probabilistic atlas with a special focus on ribs supression. Preliminary results. In: Proceedings of the IEEE Engineering in

[24] Heiberg E, Sjögren J, Ugander M, Carlsson M, Engblom H, Arheden H. Design and validation of segment—Freely available software for cardiovascular image analysis.

[25] Scientific Computing and Imaging Institute (SCI). Seg3D: Volumetric Image Segmentation and Visualization [Internet]. Available from: http://www.sci.utah.edu/cibc-software/

[26] Casero R, Burton RA, Quinn T, Bollensdorff C, Hales P, Schneider JE, et al. Cardiac valve annulus manual segmentation using computer assisted visual feedback in three-dimensional image data. In: Proceedings of the IEEE Engineering in Medicine and Biology

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2389334

94 Computed Tomography - Advanced Applications

10.1118/1.2746498


## **Non-contrast CT in the Evaluation of Urinary Tract**

### **Stone Obstruction and Haematuria**

Mohammad Hammad Ather, Wasim Memon,

Wajahat Aziz and Mohammad Nasir Sulaiman

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68769

#### **Abstract**

Non-contrast computed tomography (CT) abdomen has emerged as a first line investigation in suspected upper urinary tract obstruction. Underlying causes can usually be ascertained on computed tomography of kidneys, ureters and bladder (CT KUB). However, further investigations may be required to delineate/confirm underlying pathology like ureteropelvic junction obstruction (UPJ), differentiation between obstruction and residual dilatation. Actual protocol of CT KUB for evaluation of stone disease and haematuria vary on institutional guidelines. CT KUB is not only extremely sensitive and specific in the diagnosis of stone; it is now used in the pre-operative nomograms in predicting success of various endourological interventions like percutaneous nephrolithotomy (PCNL) and shock wave lithotripsy (SWL). Determination of stone density, stone volume, stone composition, skin to stone distance, presence of ureteral wall oedema, perinephric oedema are highly predictive of stone free rate. CT recognition of various anomalies, presence of retro-renal colon, horse-shoe kidney, malrotation, etc. can help in better planning to avoid complications. One of the major limitations of CT is the radiation dose, besides cost and availability. Modification in technique and technological innovation has resulted in significant dose reduction from 4.5 to about 1 mSv.

**Keywords:** CT KUB, non-contrast-enhanced CT, low-dose CT, endourology, PCNL, SWL, NCCT

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **1. Introduction**

Computed tomography of kidneys, ureters and bladder (CT KUB) is a quick non-invasive technique for diagnosis of stone disease. It was initially used in the evaluation of radiolucent stones only however, Smith et al. [1] in 1995 showed CT has superiority over intravenous urography (IVU). CT KUB subsequently became the first choice in the diagnostic imaging of urinary tract for obstruction of stones. It has replaced IVU almost completely in the last two decades [2]. It is usually considered the initial imaging modality for suspected acute renal colic and dipstick positive haematuria in an emergency setting and initial diagnostic evaluation of upper tract obstruction. CT KUB has certain clear advantages over other urinary tract imaging for stones. It is not dependent on stone chemical composition; all stones are well seen on CT except for the Indinavir stones [3], it does not require contrast, it can be rapidly performed and can be used in planning endourological treatment.

Actual protocol of CT KUB for evaluation of stone disease and haematuria will vary depending on institutional guidelines. The general parameters are (i) non-contract examination is performed on multi-detector computed tomography scanner; (ii) supine or supine and prone patient positioning (prone has the advantage of assessing stones near the VUJ); (iii) data interpretation with the use of axial, coronal, sagittal and sometimes curved oblique images for proper evaluation; (iv) scan parameters which includes slice thickness(recommended 5 mm or less), field of view: patient size algorithm: standard technique ( 120 kV/Auto MA .5 rotation); Anatomical start point: 1 cm above the liver Anatomical stop through inferior pubic rami).

### **2. Technique/protocols**

CT KUB is a quick non-invasive technique for diagnosis of stone disease. It is usually considered the initial imaging modality for suspected acute renal colic and dipstick positive haematuria in an emergency setting. Unenhanced CT is also increasingly being used for treatment planning and post-treatment surveillance for stone recurrence.

This is a study without intravenous or oral contrast, relatively low-dose (in CT terms), and has a very high sensitivity for the detection of renal and ureteric stones. CT KUB allows a rapid, contrast-free, anatomically accurate diagnosis of urolithiasis with a sensitivity of 97–98% and a specificity of 96–100%.

The effective dose of a standard CT KUB examination has been estimated to be between 3 and 5 mSv, which is up to three times that for intravenous pyelography. However, radiation dose in CT KUB is gradually decreasing with the introduction of ultra-low radiation dose CT KUB (0.5–0.7 mSv). These doses are almost comparable to plain film KUB and have shown favourable outcomes similar to standard radiation dose CT KUB. Reductions in CT dose inherently create an increase in image noise. Therefore, a balance has to be found between image quality (signal-to-noise ratio) and restraining the radiation dose.

In comparison to conventional CT, spiral CT is significantly faster. It thus allows acquisition of a complete data set in a single breath-hold and prevents the misregistration of slice location that is typical of conventional CT. In addition, multi-slice spiral CT reduces the time needed for image acquisition, allowing for thinner slice collimation and retrospective reconstruction of thin slices to review challenging areas of analysis.

From the top of the kidneys through the base of the bladder (mid-liver [T-12] through symphysis pubis), data acquisition is uninterrupted using a maximum of 5-mm collimation with table speed of 5 mm/s. Slice collimation with multi-slice CT is usually 2.5–3 mm with table speed up to 5 mm/s.

Multislice technique allows slices as thin as 1 mm to be obtained for problem solving. The thinner slices can be viewed retrospectively without rescanning the patient. Thin slices enable identification of extremely small sized calculi that may be overlooked if the slices are thicker.

Turning the patient to a prone position permits differentiation of stones impacted at the ureterovesical junction from stones that have already passed into the bladder.

Actual protocol of CT KUB for evaluation of stone disease and haematuria will vary depending upon institutional guidelines but following are the general parameters:


Scan parameters:

**1. Introduction**

98 Computed Tomography - Advanced Applications

**2. Technique/protocols**

a specificity of 96–100%.

Computed tomography of kidneys, ureters and bladder (CT KUB) is a quick non-invasive technique for diagnosis of stone disease. It was initially used in the evaluation of radiolucent stones only however, Smith et al. [1] in 1995 showed CT has superiority over intravenous urography (IVU). CT KUB subsequently became the first choice in the diagnostic imaging of urinary tract for obstruction of stones. It has replaced IVU almost completely in the last two decades [2]. It is usually considered the initial imaging modality for suspected acute renal colic and dipstick positive haematuria in an emergency setting and initial diagnostic evaluation of upper tract obstruction. CT KUB has certain clear advantages over other urinary tract imaging for stones. It is not dependent on stone chemical composition; all stones are well seen on CT except for the Indinavir stones [3], it does not require contrast, it can be rapidly

Actual protocol of CT KUB for evaluation of stone disease and haematuria will vary depending on institutional guidelines. The general parameters are (i) non-contract examination is performed on multi-detector computed tomography scanner; (ii) supine or supine and prone patient positioning (prone has the advantage of assessing stones near the VUJ); (iii) data interpretation with the use of axial, coronal, sagittal and sometimes curved oblique images for proper evaluation; (iv) scan parameters which includes slice thickness(recommended 5 mm or less), field of view: patient size algorithm: standard technique ( 120 kV/Auto MA .5 rotation); Anatomical start point:

CT KUB is a quick non-invasive technique for diagnosis of stone disease. It is usually considered the initial imaging modality for suspected acute renal colic and dipstick positive haematuria in an emergency setting. Unenhanced CT is also increasingly being used for treatment

This is a study without intravenous or oral contrast, relatively low-dose (in CT terms), and has a very high sensitivity for the detection of renal and ureteric stones. CT KUB allows a rapid, contrast-free, anatomically accurate diagnosis of urolithiasis with a sensitivity of 97–98% and

The effective dose of a standard CT KUB examination has been estimated to be between 3 and 5 mSv, which is up to three times that for intravenous pyelography. However, radiation dose in CT KUB is gradually decreasing with the introduction of ultra-low radiation dose CT KUB (0.5–0.7 mSv). These doses are almost comparable to plain film KUB and have shown favourable outcomes similar to standard radiation dose CT KUB. Reductions in CT dose inherently create an increase in image noise. Therefore, a balance has to be found between

In comparison to conventional CT, spiral CT is significantly faster. It thus allows acquisition of a complete data set in a single breath-hold and prevents the misregistration of slice location

performed and can be used in planning endourological treatment.

1 cm above the liver Anatomical stop through inferior pubic rami).

planning and post-treatment surveillance for stone recurrence.

image quality (signal-to-noise ratio) and restraining the radiation dose.


Dual-energy CT scanning is a new technique that can more correctly distinguish different stone types. It involves acquiring CT data at two different X-ray energies (80 and 140 peak kilovoltage [kVp]). Post-processing software can make use of the different attenuation properties of calculi of various chemical compositions at low and high X-ray energies.

Decreased exposure is most commonly achieved by modifying tube current and applying new image reconstruction algorithms. Low-dose CT has been shown to maintain diagnostic accuracy compared with standard-dose CT, even in overweight and obese patients when using automated tube current modulation.

#### **2.1. Indication and uses of CT KUB**

A clinical decision to order CT KUB has to be made in two different clinical presentations. First is a patient with flank pain presenting in emergency department. The classic clinical presentation of a young man writhing in pain is usually distinctive. However, atypical presentations are not uncommon. CT KUB is still reasonable first-line investigation for all patients presenting in emergency with flank pain as it increases diagnostic accuracy in atypical cases and can detect other pathologies. In a study of 1500 consecutive CT examinations in patients with flank pain, 14% had CT findings other than stone requiring immediate or deferred treatment [4]. Although this diagnostic superiority of CT KUB for flank pain is well established, recent studies have questioned whether it influences management decision in emergency setting. A multicentre, randomised controlled trial of carefully selected patients with suspected nephrolithiasis compared ultrasound with CT KUB and concluded that initial ultrasound decreases cumulative radiation exposure by obviating need of CT in some patients without significant difference in missing high-risk diagnoses, serious adverse events and re-admissions [5].

In a clinical setting, the choice of CT KUB versus ultrasound for initial diagnostic imaging in patients with flank pain should be individualised. Patients who are obese, clearly sick or have associated gross/microscopic haematuria are more likely to benefit from CT scan. On the other hand, children, pregnant women and those assessed to have musculoskeletal pain clinically are more appropriate for ultrasound first approach. Available local resources, for example, expert sonologist should also be taken into account when making this decision.

### **3. Evaluation of obstruction**

Second clinical setting requiring CT KUB is incidental finding of hydronephrosis on ultrasound. The decision to request CT KUB will depend on information available on ultrasound and suspected cause of underlying obstruction. In some cases, ultrasound will provide sufficient information to decide further management. For instance, in classic ureteropelvic junction obstruction (UPJO) in a child, ultrasound alone would provide enough anatomical detail to proceed for radionuclide imaging. Similarly small ureterovesical junction stone seen clearly on ultrasound combined with clinical picture is usually sufficient to proceed for management decision. CT KUB is suitable if renal or ureteric stones are suspected as underlying cause of hydronephrosis or a benign pathology, for example, ureteric stricture/retroperitoneal fibrosis is presumed after history and examination. If an upper tract tumour or extrinsic malignant obstruction is suspected, a contrast-enhanced study is more appropriate.

Upper tract obstruction may lead to derangement in renal function and it is not uncommon to find raised creatinine in such patients especially if obstruction is bilateral. European Society of Urogenital Radiology recommends that an estimated glomerular filtration rate (eGFR) of less than 45 ml/min/1.73 m<sup>2</sup> particularly with other risk factors, for example, diabetic nephropathy and dehydration increases the risk of contrast-induced nephropathy (CIN) [6]. This effectively precludes contrast-enhanced study in such patients. CT KUB is helpful in excluding calculi and may even provide a definitive diagnosis in up to 40% cases of non-calculus obstruction [7]. MR urography will be required for making a definitive diagnosis in remaining cases.

**2.1. Indication and uses of CT KUB**

100 Computed Tomography - Advanced Applications

and re-admissions [5].

**3. Evaluation of obstruction**

than 45 ml/min/1.73 m<sup>2</sup>

A clinical decision to order CT KUB has to be made in two different clinical presentations. First is a patient with flank pain presenting in emergency department. The classic clinical presentation of a young man writhing in pain is usually distinctive. However, atypical presentations are not uncommon. CT KUB is still reasonable first-line investigation for all patients presenting in emergency with flank pain as it increases diagnostic accuracy in atypical cases and can detect other pathologies. In a study of 1500 consecutive CT examinations in patients with flank pain, 14% had CT findings other than stone requiring immediate or deferred treatment [4]. Although this diagnostic superiority of CT KUB for flank pain is well established, recent studies have questioned whether it influences management decision in emergency setting. A multicentre, randomised controlled trial of carefully selected patients with suspected nephrolithiasis compared ultrasound with CT KUB and concluded that initial ultrasound decreases cumulative radiation exposure by obviating need of CT in some patients without significant difference in missing high-risk diagnoses, serious adverse events

In a clinical setting, the choice of CT KUB versus ultrasound for initial diagnostic imaging in patients with flank pain should be individualised. Patients who are obese, clearly sick or have associated gross/microscopic haematuria are more likely to benefit from CT scan. On the other hand, children, pregnant women and those assessed to have musculoskeletal pain clinically are more appropriate for ultrasound first approach. Available local resources, for example,

Second clinical setting requiring CT KUB is incidental finding of hydronephrosis on ultrasound. The decision to request CT KUB will depend on information available on ultrasound and suspected cause of underlying obstruction. In some cases, ultrasound will provide sufficient information to decide further management. For instance, in classic ureteropelvic junction obstruction (UPJO) in a child, ultrasound alone would provide enough anatomical detail to proceed for radionuclide imaging. Similarly small ureterovesical junction stone seen clearly on ultrasound combined with clinical picture is usually sufficient to proceed for management decision. CT KUB is suitable if renal or ureteric stones are suspected as underlying cause of hydronephrosis or a benign pathology, for example, ureteric stricture/retroperitoneal fibrosis is presumed after history and examination. If an upper tract tumour or extrinsic malignant

Upper tract obstruction may lead to derangement in renal function and it is not uncommon to find raised creatinine in such patients especially if obstruction is bilateral. European Society of Urogenital Radiology recommends that an estimated glomerular filtration rate (eGFR) of less

and dehydration increases the risk of contrast-induced nephropathy (CIN) [6]. This effectively precludes contrast-enhanced study in such patients. CT KUB is helpful in excluding calculi

particularly with other risk factors, for example, diabetic nephropathy

expert sonologist should also be taken into account when making this decision.

obstruction is suspected, a contrast-enhanced study is more appropriate.

CT KUB is currently considered as the first line imaging in the evaluation of stone and obstruction (**Figure 1**) and is preferred over an IVU [2]. This is in view of high sensitivity and specificity of CT over other imaging modalities. It is particularly useful in the diagnosis of ureteral stones (**Figures 1** and **2**) with sensitivity of 95–98% and specificity of 96–98% [8, 9]. It is of particular value in patients with renal failure, which precludes use of intravenous contrast, and ultrasound has limited value [10]. The sensitivity of ultrasound in the evaluation

**Figure 1.** (a) Hydronephrosis (asterik), reduced peripelvic fat (white arrow) and increased perinephric fat stranding (black arrow) as compared to contralateral side and (b). CT KUB axial, sagittal and coronal sections demonstrating multiple calcific densities near the bulbar urethra likely representing urethral diverticulum with stone formation.

**Figure 2.** CT KUB axial and coronal sections demonstrating an obstructing right proximal ureteric calculus.

of ureteral stones when compared with CT KUB is only 46% and for hydroureter in half of the cases. CT KUB in the evaluation of ureteral stones is able to identify ureteral dilation in 83%, hydronephrosis in 80% and perinephric oedema in 59%, and ipsilateral nephromegaly in 57.2% of cases [11].

### **4. Evaluation of haematuria**

In addition to diagnosis of stone and obstruction, it is also used in the work up haematuria. Asymptomatic micro-haematuria (AMH) is relatively common and is often not associated with urinary tract malignancies. The current guidelines indicate evaluation of upper urinary tract with contrast-enhanced CT (CECT). This often leads to identification of extra-urinary tract abnormalities. The diagnoses of such conditions often require extensive work for most conditions, which are inconsequential [12]. These are often observed on non-contrast CT imaging as well [13]. In vast majority of cases, ASH is idiopathic followed small renal stones (**Figure 3**) and other benign causes. Ultrasound is often the initial imaging, however, CT KUB can be used in lieu.

of ureteral stones when compared with CT KUB is only 46% and for hydroureter in half of the cases. CT KUB in the evaluation of ureteral stones is able to identify ureteral dilation in 83%, hydronephrosis in 80% and perinephric oedema in 59%, and ipsilateral nephromegaly

**Figure 2.** CT KUB axial and coronal sections demonstrating an obstructing right proximal ureteric calculus.

In addition to diagnosis of stone and obstruction, it is also used in the work up haematuria. Asymptomatic micro-haematuria (AMH) is relatively common and is often not associated

in 57.2% of cases [11].

**4. Evaluation of haematuria**

102 Computed Tomography - Advanced Applications

**Figure 3.** CT KUB axial and coronal sections demonstrating a left renal pelvis calculus (a and b) and left distal ureteric calculus (c).

#### **4.1. In emergency room setting**

Acute onset flank pain suggestive of ureteral obstruction is a common presentation in the emergency room (ER) setting. Introduction of CT has decreased the time in decision-making [14] about the possible aetiology of cause of flank pain [15, 16]. Clinical evaluation and ultrasound often makes it difficult to differentiate ureteral obstruction from other pathologies. However, CT not only quickly identifies urolithiasis but also identifies other causes of flank pain [17]. This includes both genitourinary and extra-genitourinary abnormalities. Stones from ureter-vesical junction sometimes pass into the urethra (**Figure 4**) without significant changes in symptoms, these can be diagnosed by careful inspection of the CT.

Initial clinical evaluation including dipstick test for micro-haematuria also lack sensitivity. Li et al. [18] noted during the period of 4 years that there were 159,083 emergency visits. During this period, 397 had urolithiasis, in these patients absence of haematuria was noted in 9% (95% confidence interval 7–12%). The next step in the management of patients with stone

**Figure 4.** CT KUB axial, coronal and sagittal sections demonstrating a calculus in the prostatic urethra.

is to determine the extent of obstruction and of any complications from obstruction and stone. None of the conventional imaging, that is, IVU, ultrasound and plain X-ray KUB is sensitive enough to answer the question. CT KUB due to its high specificity and sensitivity to diagnose ureteral stones is ideal imaging in such a situation. However, CT without contrast has limitations being a non-contrast study. Secondary signs of obstruction like perinephric, periureteral stranding and unilateral nephromegaly are sometimes helpful. Bird et al. [19] in a study assess the significance of secondary signs of obstruction on CT KUB and noted that they do not correlate with degrees of obstruction on MAG-3. The authors suggested use of CT KUB in combination with radioisotope scans [9]. This is cumbersome particularly in an emergency room setting. As an alternate, Kravchick et al. [20] suggested the use of dynamic renal sonography in combination with CT KUB, particularly in patients with raised white cell count and stone larger than 4 mm. This is particularly useful in triaging patients who need admission in the hospital.

#### **4.2. In elective clinical situation**

Modern endourological interventions are becoming increasingly minimally invasive. Percutaneous nephrolithotomy is performed with 24–30 Fr. Amplatz; however, finer nephroscope has led to the introduction of mini (2001), micro (2011) and ultra mini (2013) [21]. Planning for these interventions require precise pre-operative assessment of stone size, location and anatomical abnormalities including caliceal narrowing, presence of caliceal diverticulum, etc. CT can be instrumental in making pre-operative assessment. It has been seen that increasing stone volume can influence post-operative complication rate. It is being observed that >4 cm stones are associated with significantly higher rate of post-operative pyrexia and need for transfusion [13].

### **4.3. Radiological signs of urinary obstruction**

### *4.3.1. CT beyond the diagnosis of stone*

**Figure 4.** CT KUB axial, coronal and sagittal sections demonstrating a calculus in the prostatic urethra.

**4.1. In emergency room setting**

104 Computed Tomography - Advanced Applications

Acute onset flank pain suggestive of ureteral obstruction is a common presentation in the emergency room (ER) setting. Introduction of CT has decreased the time in decision-making [14] about the possible aetiology of cause of flank pain [15, 16]. Clinical evaluation and ultrasound often makes it difficult to differentiate ureteral obstruction from other pathologies. However, CT not only quickly identifies urolithiasis but also identifies other causes of flank pain [17]. This includes both genitourinary and extra-genitourinary abnormalities. Stones from ureter-vesical junction sometimes pass into the urethra (**Figure 4**) without significant

Initial clinical evaluation including dipstick test for micro-haematuria also lack sensitivity. Li et al. [18] noted during the period of 4 years that there were 159,083 emergency visits. During this period, 397 had urolithiasis, in these patients absence of haematuria was noted in 9% (95% confidence interval 7–12%). The next step in the management of patients with stone

changes in symptoms, these can be diagnosed by careful inspection of the CT.

The sensitivity and specificity of CT in the diagnosis of stone is well established. Even small stones, which would otherwise be missed on most other imaging, can be identified on CT. However, CT has utility beyond recognising the presence of stone in the urinary tract. It can be used in planning endourological interventions. Stone size, composition, location, skin to stone distance, etc. are some of the well recognised parameters used in the risk stratification and predicting success of treatment [22].

Shock wave lithotripsy (SWL) is the most minimally invasive treatment in the management of urolithiasis. Prediction of success for renal stones is often done on a CT KUB using estimation of stone volume, density (using Hounsfield Units) and skin to stone distance [23]. In a recent work, Park et al. [24] noted that BMI and perinephric oedema in addition to stone density are independent predictors of success of SWL. Ureteral stones requiring interventional treatment are either treated by SWL or ureteroscopy. Success of ureteral stone is dependent on stone size [25]. The success of treatment is assessed not only by stone free rate but also need for ancillary treatment and number of sessions required to clear the stone [26]. One important factor responsible for failed medical SWL for ureteral stone is stone impaction, defined as stone stuck in one location for over 1 month. Sarica et al. [27] recently noted that of all the evaluated stone- and patient-related factors, only ureteral wall thickness at the impacted stone site independently predicted shock wave lithotripsy success.

Stone size is one of the most important parameter in deciding the management of ureteral stone. In a recent work, Soomro et al. [28] compared the mean stone size, as measured on bone window versus standard soft-tissue window setting using multi-detector computed tomography (MDCT) in patients with a solitary ureteric stone. They noted that the stone size measured using the soft-tissue window setting on a MDCT is significantly different from the measurement on the bone windows. Earlier work also indicated that the transverse stone diameter on axial images of CT KUB underestimates the size of ureteric stone [29]. The authors suggested that coronal reformatted images be used for size estimation.

Percutaneous nephrolithotomy (PCNL) is a minimally invasive treatment modality used in the management of >20 mm kidney stones, and as such, is considered as the primary modality by EAU and AUA guidelines [30, 31]. Predicting complications and success of percutaneous surgery for urolithiasis can now be reliably done using one of the several nephrolithometry scores [22]. Nephrolithometry scoring systems are based on pre-operative stone and patient features and they demonstrate and stratify relationships between kidney's anatomy and stones. Currently there are three scoring systems; Guy's score [32] described in 2011, S.T.O.N.E. nephrolithometry system [33] and CROES nephrolithometry nomogram [34] in 2013. In a recent work by Choi et al. comparing these three scoring systems for tubeless PCNL, noted that Guy's stone score was the only significant predictive factor for stone free and complication rates. However, Tailly et al. [35] earlier noted no difference in the ability to predict stone free rate comparing the three scoring systems after PCNL.

PCNL is safe surgical procedure and is not associated with high grade on Clavien grading. The most frequently reported complication following PCNL is infection and haemorrhage, however one of the most devastating complication is a surrounding organ injury including bowel injury. According to the Clavien-Dindo classification of surgical complications, colonic injury is regarded as a stage IVa complication. The incidence of colon injury is reported to be 0.3–0.5%, however in a large recently reported series, AslZare et al. [36] noted 11 cases in 5260 cases of PCNL. Colonic injuries are seen in patients with retro-renal colon, the prevalence of retro-renal colon in males to be 13.6% on the right and 11.9% on the left, whilst in females it was 13.4% on the right and 26.2% on the left [37]. CT KUB is instrumental in recognising retro-renal colon prior to PCNL. Most of the colonic injuries are now managed conservatively with drainage of colon via percutaneous drain, insertion of JJ stent to drain kidney, intravenous antibiotics and bowel rest by giving intravenous nutrition.

### **4.4. Features of upper tract obstruction**

Once a CT KUB abdomen is ordered for suspected upper tract obstruction, it should be reviewed for secondary radiological signs of obstruction, site of obstruction and underlying pathology. Moreover, associated findings, for example, dilated appendix, ovarian cysts, spinal pathologies should be considered and systematically reviewed.

Classic secondary radiological signs on CT KUB suggesting upper tract obstruction include: dilatation of renal pelvis, dilated ureter and perinephric stranding (**Figure 1a** and **b**). Renal pelvis is identifiable as area of low attenuation compared to adjacent renal parenchyma. Dilatation of renal pelvis (hydronephrosis) usually appears as anterior and medial bulging of this low attenuation structure. In some cases, dilated renal pelvis may be difficult to differentiate from a prominent extra renal pelvis. However, dilated calices that obliterate the renal sinus fat help in making this differentiation. CT is also valuable in differentiating between stone and stent (**Figure 5**), particularly with the use of bone windows.

defined as stone stuck in one location for over 1 month. Sarica et al. [27] recently noted that of all the evaluated stone- and patient-related factors, only ureteral wall thickness at the

Stone size is one of the most important parameter in deciding the management of ureteral stone. In a recent work, Soomro et al. [28] compared the mean stone size, as measured on bone window versus standard soft-tissue window setting using multi-detector computed tomography (MDCT) in patients with a solitary ureteric stone. They noted that the stone size measured using the soft-tissue window setting on a MDCT is significantly different from the measurement on the bone windows. Earlier work also indicated that the transverse stone diameter on axial images of CT KUB underestimates the size of ureteric stone [29]. The authors suggested that coronal re-

Percutaneous nephrolithotomy (PCNL) is a minimally invasive treatment modality used in the management of >20 mm kidney stones, and as such, is considered as the primary modality by EAU and AUA guidelines [30, 31]. Predicting complications and success of percutaneous surgery for urolithiasis can now be reliably done using one of the several nephrolithometry scores [22]. Nephrolithometry scoring systems are based on pre-operative stone and patient features and they demonstrate and stratify relationships between kidney's anatomy and stones. Currently there are three scoring systems; Guy's score [32] described in 2011, S.T.O.N.E. nephrolithometry system [33] and CROES nephrolithometry nomogram [34] in 2013. In a recent work by Choi et al. comparing these three scoring systems for tubeless PCNL, noted that Guy's stone score was the only significant predictive factor for stone free and complication rates. However, Tailly et al. [35] earlier noted no difference in the ability to

PCNL is safe surgical procedure and is not associated with high grade on Clavien grading. The most frequently reported complication following PCNL is infection and haemorrhage, however one of the most devastating complication is a surrounding organ injury including bowel injury. According to the Clavien-Dindo classification of surgical complications, colonic injury is regarded as a stage IVa complication. The incidence of colon injury is reported to be 0.3–0.5%, however in a large recently reported series, AslZare et al. [36] noted 11 cases in 5260 cases of PCNL. Colonic injuries are seen in patients with retro-renal colon, the prevalence of retro-renal colon in males to be 13.6% on the right and 11.9% on the left, whilst in females it was 13.4% on the right and 26.2% on the left [37]. CT KUB is instrumental in recognising retro-renal colon prior to PCNL. Most of the colonic injuries are now managed conservatively with drainage of colon via percutaneous drain, insertion of JJ stent to drain kidney, intravenous antibiotics and bowel rest by giving intravenous

Once a CT KUB abdomen is ordered for suspected upper tract obstruction, it should be reviewed for secondary radiological signs of obstruction, site of obstruction and underlying pathology. Moreover, associated findings, for example, dilated appendix, ovarian cysts,

impacted stone site independently predicted shock wave lithotripsy success.

predict stone free rate comparing the three scoring systems after PCNL.

spinal pathologies should be considered and systematically reviewed.

formatted images be used for size estimation.

106 Computed Tomography - Advanced Applications

nutrition.

**4.4. Features of upper tract obstruction**

**Figure 5.** CT KUB axial, coronal and sagittal sections demonstrating a left-sided double J stent in place.

An assessment of degree of obstruction can also be made on CT KUB (**Table 1**). The Society of Foetal Ultrasound first described the grading system for hydronephrosis [38]. Similar description has also been applied to other imaging modalities like intravenous urography and CT [39].

Dilatation of ureter when present should be traced down to the site of obstruction, to differentiate between phlobolith and stone (**Figure 6**). The dilated ureter is usually traceable from


**Table 1.** Degree and grade of hydronephrosis and its description.

**Figure 6.** CT KUB axial and coronal sections demonstrating s in the pelvis.

ureteropelvic junction when viewing coronal sections at a workstation. However, combining information from both axial and coronal images may be needed, especially for the lower ureter obscured by bowel loops or iliac vessels (**Figure 6**). Curved planar re-formatted images have been utilised to provide images mimicking a contrast-enhanced study and improve diagnostic yield for ureteric lesions [40]. UVJ stones could be differentiated from vesical stones by prone CT of the bladder area (**Figure 7**).

An assessment of degree of obstruction can also be made on CT KUB (**Table 1**). The Society of Foetal Ultrasound first described the grading system for hydronephrosis [38]. Similar description has also been applied to other imaging modalities like intravenous urography and CT [39]. Dilatation of ureter when present should be traced down to the site of obstruction, to differentiate between phlobolith and stone (**Figure 6**). The dilated ureter is usually traceable from

papillary impression with or without cortical thinning

associated cortical thinning

Grade 0 No dilation caliceal walls opposed to each other Grade 1 Mild Dilation of renal pelvis without dilation of the calyces Grade 2 Mild Dilation of renal pelvis and calyces, no cortical thinning Grade 3 Moderate Dilation of the renal pelvis and calices with blunting of

Grade 4 Severe Gross dilation of the renal pelvis and calices with

**Grade Degree Description**

108 Computed Tomography - Advanced Applications

**Table 1.** Degree and grade of hydronephrosis and its description.

**Figure 6.** CT KUB axial and coronal sections demonstrating s in the pelvis.

Once tracing the dilatation of ureter identifies site of obstruction, it should be reviewed for intraluminal, luminal or extra luminal obstructing lesions. Intraluminal pathologies include stones, blood clot and papilla. Fortunately the most common obstructing lesion, that is, stone is almost always CT dense and easily identifiable. In the absence of obstructing stone and positive radiological signs of obstruction, one should consider differential diagnosis of passed

**Figure 7.** CT KUB axial supine and prone positions demonstrating a left-sided VUJ calculus.

stone, pyelonephritis or obstruction caused by lesion not visible on CT KUB. Such lesions include blood clot, papilla and Indinavir stone. Reviewing clinical picture can narrow these differentials. For instance, Indinavir stone occurs only in patients treated with this protease inhibitor for HIV and papillary necrosis is more common in diabetic patients with analgesic nephropathy.

Presence of ureteric thickening or narrowing at the site of obstruction is suggestive of ureteric stricture. Differentiating benign from malignant strictures would require a contrast-enhanced study or endoscopy. Extramural lesions causing obstruction include pelvic tumour, retroperitoneal mass and retroperitoneal fibrosis. Retroperitoneal fibrosis is classically seen as irregular, well-defined iso-dense mass surrounding aortic bifurcation. It usually follows the common iliac arteries and expands laterally to trap ureters. Differentiation from retroperitoneal malignancies may be difficult even after contrast-enhanced study. Enhancement after contrast administration is variable and depends on degree of metabolic activity and on-going fibrosis. Presence of bone destruction and displacement of major vessels will be suggestive of malignant process [41].

#### **4.5. Limitations of CT KUB in diagnosis**

Limitations of CT KUB include the fact that CT has limited spatial resolution. Therefore, its negative predictive value in completely excluding sub-millimetre calculi and small stone fragments is significantly less than its negative predictive value in excluding larger calculi (>4 mm). In addition, repeated use of CT in patients with recurrent urolithiasis can result in a substantial cumulative dose.

Details of pelvicalyceal anatomy may not be apparent on non-contrast-enhanced study. Intravenous urography or CT urography may be required if specific anatomical details are needed for making a management decision, for example, bifid system, stone in a calyceal diverticulum or narrow lower pole infundibulum.

CT KUB is a static study and the abnormalities related to urinary dynamics, that is, UPJ obstruction, obstructive versus residual dilatation of the collecting system, etc. cannot be appreciated. Complementing CT KUB with either MAG3 scan or dynamic Doppler ultrasound are some of the modifications recommended.

The other major limitation of the CT KUB is the risk of radiation exposure. Dose reduction by various technical modifications has been recommended [42]. In a systematic review, Xiang et al. [43] noted that lowering the dose of radiation of CT does not negatively impact the sensitivity and specificity in the diagnosis of stone and obstruction. They noted that low dose CT KUB has a cumulative sensitivity of 93% and specificity of about 97% [19].

In a meta-analysis reported by Niemann and colleagues [44] some 9 yeas back, they noted that dose reduction attempts resulted in mean dose of less than 3 mSv without jeopardizing the pooled sensitivity (97%) and specificity (95%). However in the last decade, there has been significant interval improvement with iterative reconstruction techniques, detector series and arrangements. These modifications have allowed a further reduction in dose to <1 mSv [45]. This is quite comparable to plain X-ray KUB at 0.7 mSv [46].

### **5. Conclusions**

stone, pyelonephritis or obstruction caused by lesion not visible on CT KUB. Such lesions include blood clot, papilla and Indinavir stone. Reviewing clinical picture can narrow these differentials. For instance, Indinavir stone occurs only in patients treated with this protease inhibitor for HIV and papillary necrosis is more common in diabetic patients with analgesic

Presence of ureteric thickening or narrowing at the site of obstruction is suggestive of ureteric stricture. Differentiating benign from malignant strictures would require a contrast-enhanced study or endoscopy. Extramural lesions causing obstruction include pelvic tumour, retroperitoneal mass and retroperitoneal fibrosis. Retroperitoneal fibrosis is classically seen as irregular, well-defined iso-dense mass surrounding aortic bifurcation. It usually follows the common iliac arteries and expands laterally to trap ureters. Differentiation from retroperitoneal malignancies may be difficult even after contrast-enhanced study. Enhancement after contrast administration is variable and depends on degree of metabolic activity and on-going fibrosis. Presence of bone destruction and displacement of major vessels will be suggestive of malignant

Limitations of CT KUB include the fact that CT has limited spatial resolution. Therefore, its negative predictive value in completely excluding sub-millimetre calculi and small stone fragments is significantly less than its negative predictive value in excluding larger calculi (>4 mm). In addition, repeated use of CT in patients with recurrent urolithiasis can result in a

Details of pelvicalyceal anatomy may not be apparent on non-contrast-enhanced study. Intravenous urography or CT urography may be required if specific anatomical details are needed for making a management decision, for example, bifid system, stone in a calyceal

CT KUB is a static study and the abnormalities related to urinary dynamics, that is, UPJ obstruction, obstructive versus residual dilatation of the collecting system, etc. cannot be appreciated. Complementing CT KUB with either MAG3 scan or dynamic Doppler ultra-

The other major limitation of the CT KUB is the risk of radiation exposure. Dose reduction by various technical modifications has been recommended [42]. In a systematic review, Xiang et al. [43] noted that lowering the dose of radiation of CT does not negatively impact the sensitivity and specificity in the diagnosis of stone and obstruction. They noted that low dose CT KUB has

In a meta-analysis reported by Niemann and colleagues [44] some 9 yeas back, they noted that dose reduction attempts resulted in mean dose of less than 3 mSv without jeopardizing the pooled sensitivity (97%) and specificity (95%). However in the last decade, there has been significant interval improvement with iterative reconstruction techniques, detector series and arrangements. These modifications have allowed a further reduction in dose to <1 mSv [45].

nephropathy.

110 Computed Tomography - Advanced Applications

process [41].

**4.5. Limitations of CT KUB in diagnosis**

diverticulum or narrow lower pole infundibulum.

sound are some of the modifications recommended.

a cumulative sensitivity of 93% and specificity of about 97% [19].

This is quite comparable to plain X-ray KUB at 0.7 mSv [46].

substantial cumulative dose.

Non-contrast CT abdomen has emerged as first line investigation in suspected upper tract obstruction. Underlying cause can usually be ascertained on CT KUB. However, further investigations may be required to delineate/confirm underlying pathology like UPJ obstruction, differentiation between obstruction and residual dilatation, etc. CT KUB is not only extremely sensitive and specific in the diagnosis of stone; it is now used in the pre-operative nomograms in predicting success of various endourological interventions like PCNL an SWL. Determination of stone density, stone volume, stone composition, skin to stone distance, presence of ureteral wall oedema, perinephric oedema are highly predictive of stone free rate. CT recognition of various anomalies, presence of retro-renal colon, horse-shoe kidney, malrotation, etc. can help in better planning to avoid complication. One of the major limitations of CT is the radiation dose. Modification in technique and technological innovation has resulted in significant dose reduction from 4.5 mSV to about 1 mSv.

### **Author details**

Mohammad Hammad Ather\*, Wasim Memon, Wajahat Aziz and Mohammad Nasir Sulaiman

\*Address all correspondence to: hammad.ather@aku.edu

Aga Khan University, Karachi, Pakistan

### **References**


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[16] Ather MH, Faizullah K, Achakzai I, Siwani R, Irani F. Alternate and incidental diagnoses on noncontrast-enhanced spiral computed tomography for acute flank pain. Urology

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### **Cone Beam Computed Tomography in Orthodontics**

Emine Kaygısız and Tuba Tortop

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68555

#### **Abstract**

Cone beam computed tomography (CBCT) is an important source of three‐dimensional volumetric data in clinical orthodontics. Due to the progress in the technology of CBCT, for orthodontic clinical diagnosis, treatment and follow‐up, CBCT supply much more reliable information compared to conventional radiography. The most justified indica‐ tions for the use of CBCT in orthodontics are the existence of impacted and transposed teeth. For the management of the impacted teeth, CBCT enhances the ability to localize these teeth accurately and to assess root resorption of adjacent teeth. Patients with cranio‐ facial anomalies like cleft palate cases, the abnormalities of the temporomandibular joint contributing malocclusion, evaluation of airway morphology in obstructive sleep apnea cases, patients needing maxillary expansion or planning orthognathic surgery in severe skeletal discrepancies are also listed among the indications of using CBCT in orthodon‐ tics. CBCT is useful in identifying optimal site location for temporary skeletal anchorage device. The use of CBCT for the assessment of treatment outcomes and evaluation of cervical vertebral maturation are still controversial issues. It should be kept in mind that before using CBCT, justification and evaluation of risks and benefits are needed. In order to minimize the radiation dose, the exam should include only the areas of interest.

**Keywords:** cone beam computed tomography, orthodontics, impacted canine, orthodontic treatment planning, root resorption

### **1. Introduction**

The key of a successful orthodontic treatment is an accurate diagnosis, growth evaluation and treatment planning. Diagnostic records for an orthodontic treatment planning generally begin with history and intraoral and extraoral examination of the patient. Dental casts, intra‐ oral and extraoral photographs are also routine diagnostic materials. Imaging is a neces‐ sary diagnostic tool in the practice of orthodontics. For radiographic evaluation, panoramic

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

radiograph, periapical views, upper occlusal radiograph and lateral cephalometric radio‐ graph are obtained if indicated. Imaging should answer the questions that cannot be solved clinically. By using radiographic examination, it is possible to confirm or rule out clinical findings [1].

In recent years, orthodontists have begun to use three‐dimensional (3D) cone beam com‐ puted tomography (CBCT) images to overcome the inadequateness of two‐dimensional (2D) radiographic records. When computed tomography was first introduced into the dental field, because of the high radiation dose, it is not preferred for orthodontic diagnosis. The technol‐ ogy has been evolving ever since, resulting in a reduction in radiation dose and relatively low cost of CBCT systems, so they become popular to visualize the craniofacial complex in three dimensions.

In some studies, it has been suggested that different options for orthodontic treatment plans in some specific cases may change due to use of CBCT [2–4]. Orthodontists should know how to use the radiographic records and what they offer, before deciding which tool they will use [1].

### **2. Advantages and disadvantages of using CBCT in orthodontics**

Although there has been considerable interest in using CBCT as a part of routine orthodon‐ tic management, diverse results about the advantages, disadvantages and indications were noted in the literature.

The review of recent literature reveals some advantages [1, 5–15] and disadvantages [16–20] as following:

### **2.1. Advantages**


#### **2.2. Disadvantages**

radiograph, periapical views, upper occlusal radiograph and lateral cephalometric radio‐ graph are obtained if indicated. Imaging should answer the questions that cannot be solved clinically. By using radiographic examination, it is possible to confirm or rule out clinical

In recent years, orthodontists have begun to use three‐dimensional (3D) cone beam com‐ puted tomography (CBCT) images to overcome the inadequateness of two‐dimensional (2D) radiographic records. When computed tomography was first introduced into the dental field, because of the high radiation dose, it is not preferred for orthodontic diagnosis. The technol‐ ogy has been evolving ever since, resulting in a reduction in radiation dose and relatively low cost of CBCT systems, so they become popular to visualize the craniofacial complex in

In some studies, it has been suggested that different options for orthodontic treatment plans in some specific cases may change due to use of CBCT [2–4]. Orthodontists should know how to use the radiographic records and what they offer, before deciding which tool they will use [1].

Although there has been considerable interest in using CBCT as a part of routine orthodon‐ tic management, diverse results about the advantages, disadvantages and indications were

The review of recent literature reveals some advantages [1, 5–15] and disadvantages [16–20]

• Accuracy of image geometry is increased, and real size 3D image is obtained by CBCT. Unlike lateral cephalometric radiographs, CBCT image is more similar to the patient, more

• CBCT images allow to make localized and specific transversal cuts to assess areas of clini‐

• For a proper diagnosis and treatment planning, sometimes temporomandibular, postero‐ anterior cephalograms, periapical, occlusal and bite‐wing radiographs are also required besides the routine panoramic and lateral cephalometric examination. But, by using CBCT technology, it is possible to produce several types of radiographic images and to construct

• The reorientation of the images, on the contrary to the lateral cephalometric radiograph,

• It eliminates the magnification, overlapping and distortion of structures.

• It is possible to assess the image from the three planes.

**2. Advantages and disadvantages of using CBCT in orthodontics**

findings [1].

118 Computed Tomography - Advanced Applications

three dimensions.

noted in the literature.

accurate and distortion‐free.

study casts from a single scan.

as following:

**2.1. Advantages**

cal interest.

is possible.


### **3. The usage of CBCT in orthodontics**

Many orthodontists interested in using CBCT during their routine diagnosis and treatment planning because of the additional diagnostic information. This brings the risk of unneces‐ sary ionizing radiation. So, it is mandatory to determine exact indications for the use of CBCT in orthodontics.

### **3.1. Impacted and transposed teeth**

Tooth impaction is a commonly observed dental anomaly which needs orthodontic treat‐ ment. The most frequent impacted teeth were mandibular wisdom teeth, which were fol‐ lowed by maxillary and mandibular canines [21]. Radiographic examinations play a more critical role than clinical examination especially in the initial diagnosis and treatment plan‐ ning of impacted teeth. For several years, radiographic evaluation of these teeth was done by using panoramic, periapical, occlusal or lateral cephalograms. These conventional two dimensional radiographs are inadequate in accurately visualizing the location, angulation, spatial position and relationships of the impacted tooth in three dimensions. So, the most justified indications for the use of CBCT in orthodontics are the existence of impacted and transposed teeth (**Figure 1a**–**c**).

For the management of the impacted teeth, CBCT enhances the ability to localize these teeth accurately, evaluate their proximity to other teeth and structures, determine the alveolar width and follicle size, the presence of pathology and assess root resorption of adjacent teeth, assist in planning surgical access and bond placement, besides determining optimal direction for the extrusion of these teeth into the oral cavity [22–25]. In particular, for impacted teeth, if exposure or forced eruption is planned, it would be possible to determine not only the posi‐ tion of tooth and dilacerated root but also the alveolar boundary conditions. Additionally, it would be much easier to prepare the space needed for the impacted tooth as it is possible to obtain a more accurate size from CBCT images.

Haney et al. [26] reported an approximate 20% lack of agreement among clinicians on the location (palatal versus labial) of the tooth tip between the routine 2D radiographs and 3D CBCT images. Also large differences in treatment approaches were demonstrated when the two imaging methods were compared [27]. On the other hand, in another study, it was reported that the determination of canine position was not significantly different when using panoramic and CBCT systems [3].

Using CBCT improves the clinician confidence in diagnosis and treatment plan as it is helpful in defining the surgical access site, bond position and in designing mechanics [25, 26]. The orthodontists have a different perception of localization and can determine the shortest way for the impacted tooth in three planes of space while avoiding damage to neighboring teeth.

In some studies, it was suggested that orthodontic treatment planning for impacted tooth showed no differences when using 2D‐ or 3D‐based information. On the contrary, findings of some other studies showed that orthodontists changed their treatment planning derived from conventional radiographs for 25% of the impacted teeth when they viewed CBCT images [26, 28]. Alqerban et al. [4, 29] concluded that CBCT allows clinicians to obtain 3D images with visualization of cranio‐ facial structures and significantly increases the orthodontists' confidence level, with more infor‐ mation on canine localization and detection of possible root resorption on adjacent incisors [30].

When the impacted tooth did not move, CBCT is indicated. Becker et al. [31] reported that invasive cervical root resorption is a rare insidious and aggressive form of external

**3.1. Impacted and transposed teeth**

120 Computed Tomography - Advanced Applications

transposed teeth (**Figure 1a**–**c**).

obtain a more accurate size from CBCT images.

panoramic and CBCT systems [3].

Tooth impaction is a commonly observed dental anomaly which needs orthodontic treat‐ ment. The most frequent impacted teeth were mandibular wisdom teeth, which were fol‐ lowed by maxillary and mandibular canines [21]. Radiographic examinations play a more critical role than clinical examination especially in the initial diagnosis and treatment plan‐ ning of impacted teeth. For several years, radiographic evaluation of these teeth was done by using panoramic, periapical, occlusal or lateral cephalograms. These conventional two dimensional radiographs are inadequate in accurately visualizing the location, angulation, spatial position and relationships of the impacted tooth in three dimensions. So, the most justified indications for the use of CBCT in orthodontics are the existence of impacted and

For the management of the impacted teeth, CBCT enhances the ability to localize these teeth accurately, evaluate their proximity to other teeth and structures, determine the alveolar width and follicle size, the presence of pathology and assess root resorption of adjacent teeth, assist in planning surgical access and bond placement, besides determining optimal direction for the extrusion of these teeth into the oral cavity [22–25]. In particular, for impacted teeth, if exposure or forced eruption is planned, it would be possible to determine not only the posi‐ tion of tooth and dilacerated root but also the alveolar boundary conditions. Additionally, it would be much easier to prepare the space needed for the impacted tooth as it is possible to

Haney et al. [26] reported an approximate 20% lack of agreement among clinicians on the location (palatal versus labial) of the tooth tip between the routine 2D radiographs and 3D CBCT images. Also large differences in treatment approaches were demonstrated when the two imaging methods were compared [27]. On the other hand, in another study, it was reported that the determination of canine position was not significantly different when using

Using CBCT improves the clinician confidence in diagnosis and treatment plan as it is helpful in defining the surgical access site, bond position and in designing mechanics [25, 26]. The orthodontists have a different perception of localization and can determine the shortest way for the impacted tooth in three planes of space while avoiding damage to neighboring teeth.

In some studies, it was suggested that orthodontic treatment planning for impacted tooth showed no differences when using 2D‐ or 3D‐based information. On the contrary, findings of some other studies showed that orthodontists changed their treatment planning derived from conventional radiographs for 25% of the impacted teeth when they viewed CBCT images [26, 28]. Alqerban et al. [4, 29] concluded that CBCT allows clinicians to obtain 3D images with visualization of cranio‐ facial structures and significantly increases the orthodontists' confidence level, with more infor‐ mation on canine localization and detection of possible root resorption on adjacent incisors [30].

When the impacted tooth did not move, CBCT is indicated. Becker et al. [31] reported that invasive cervical root resorption is a rare insidious and aggressive form of external

**Figure 1.** (a) Panoramic view of a maxillary impacted canine. Note that in this case, FOV was restricted only to maxilla. (b) Determination of vestibular location of a maxillary impacted canine. (c) Evaluation of proximity between impacted canine and root of lateral incisor by CBCT.

root resorption and an overlooked cause of failure of orthodontic resolution of impacted canines.

CBCT minimizes superimposition artifacts and provides superior visualization of roots [24, 32]. In extraction cases with an impacted tooth, it is a much more important to decide which tooth to extract, a tooth with a resorbed root or a healthy premolar? Using CBCT images will contribute to a logical clinical outcome, as it provides superior information on root resorption.

Overall, it could be considered to increase efficiency and enhance success rates for the treatment of impacted teeth when the treatment and biomechanics are customized by using CBCT [33].

Field of view (FOV) must be determined according to the needs of the case. If the only problem is an impacted tooth, it would be logical to localize the FOV as the impacted tooth, adjacent teeth and surrounding alveolar structure. In fact, in a recent study, Wriedt et al. [30] recom‐ mended small volume FOV CBCT for impacted maxillary canines if the canine inclination on a conventional 2D panoramic radiograph exceeds 30° relative to a perpendicular midline, when adjacent root resorption is suspected, and/or when canine root dilaceration is suspected on conventional panoramic radiographs. But if an orthognathic surgical treatment plan is predicted, cephalometric and panoramic radiograph need must be considered while deter‐ mining FOV. It is advisable to refer the patient to an oral and maxillofacial radiologist with a note including clinically significant findings and request a report on the region of interest [27].

Maxillary lateral incisor root resorption is most commonly associated with canine impaction. It often remains asymptomatic, limiting early diagnosis. However, early diagnosis is impor‐ tant, because the presence or absence of root resorption will determine the treatment strategy. Furthermore, advanced root resorption can make treatment impossible [34]. Improvement in diagnostic measures for early detection and prevention is therefore essential for ensuring cor‐ rect treatment, and it might also reduce treatment time, complexity, complications and costs. It has been suggested that by using 3D images, overlapping of structures can be avoided.

Dental transposition represents a multifactorial condition. In the etiology of transposition, both genetic and environmental factors play an important role [35]. For the diagnosis and treatment planning of transposed teeth, several significant variables can be derived from CBCT imaging, especially, critical when deciding whether patient requires extraction or not. So, it would be much easier to evaluate adequately the quality and shape of teeth, location of roots and limitations of the alveolar boundary conditions around the transposed teeth by using CBCT. Kapila et al. [28] recommended to be selective about which cases may benefit from CBCT scans for assessing boundary conditions. Cases with compromised periodontal or gingival conditions, patients with narrow alveolar bone in which it would be critical to man‐ age buccolingual displacements or angulations of teeth, and cases who need shifting position of the teeth are listed as cases that will benefit from CBCT scans.

#### **3.2. Supernumerary teeth**

A supernumerary tooth may closely resemble the teeth of the group to which it belongs [36]. In supernumerary cases, radiographic examination aims to determine the localization and the morphology of the supernumerary teeth. As it is critical to decide which teeth to be extracted and which teeth to be retained, CBCT helps to precisely evaluate the position and morphology of these teeth. It is also possible to detect any contact between the supernumer‐ ary teeth and adjacent teeth and to evaluate their relation with other anatomical structures. The information obtained from CBCT images also facilitates the determination of the optimal surgical access to these teeth in order to minimize harm to adjacent teeth and to surrounding tissue [37] (**Figure 2**).

### **3.3. Root resorption**

root resorption and an overlooked cause of failure of orthodontic resolution of impacted

CBCT minimizes superimposition artifacts and provides superior visualization of roots [24, 32]. In extraction cases with an impacted tooth, it is a much more important to decide which tooth to extract, a tooth with a resorbed root or a healthy premolar? Using CBCT images will contribute

Overall, it could be considered to increase efficiency and enhance success rates for the treatment of impacted teeth when the treatment and biomechanics are customized by using CBCT [33].

Field of view (FOV) must be determined according to the needs of the case. If the only problem is an impacted tooth, it would be logical to localize the FOV as the impacted tooth, adjacent teeth and surrounding alveolar structure. In fact, in a recent study, Wriedt et al. [30] recom‐ mended small volume FOV CBCT for impacted maxillary canines if the canine inclination on a conventional 2D panoramic radiograph exceeds 30° relative to a perpendicular midline, when adjacent root resorption is suspected, and/or when canine root dilaceration is suspected on conventional panoramic radiographs. But if an orthognathic surgical treatment plan is predicted, cephalometric and panoramic radiograph need must be considered while deter‐ mining FOV. It is advisable to refer the patient to an oral and maxillofacial radiologist with a note including clinically significant findings and request a report on the region of interest [27]. Maxillary lateral incisor root resorption is most commonly associated with canine impaction. It often remains asymptomatic, limiting early diagnosis. However, early diagnosis is impor‐ tant, because the presence or absence of root resorption will determine the treatment strategy. Furthermore, advanced root resorption can make treatment impossible [34]. Improvement in diagnostic measures for early detection and prevention is therefore essential for ensuring cor‐ rect treatment, and it might also reduce treatment time, complexity, complications and costs. It has been suggested that by using 3D images, overlapping of structures can be avoided.

Dental transposition represents a multifactorial condition. In the etiology of transposition, both genetic and environmental factors play an important role [35]. For the diagnosis and treatment planning of transposed teeth, several significant variables can be derived from CBCT imaging, especially, critical when deciding whether patient requires extraction or not. So, it would be much easier to evaluate adequately the quality and shape of teeth, location of roots and limitations of the alveolar boundary conditions around the transposed teeth by using CBCT. Kapila et al. [28] recommended to be selective about which cases may benefit from CBCT scans for assessing boundary conditions. Cases with compromised periodontal or gingival conditions, patients with narrow alveolar bone in which it would be critical to man‐ age buccolingual displacements or angulations of teeth, and cases who need shifting position

A supernumerary tooth may closely resemble the teeth of the group to which it belongs [36]. In supernumerary cases, radiographic examination aims to determine the localization and the morphology of the supernumerary teeth. As it is critical to decide which teeth to be

of the teeth are listed as cases that will benefit from CBCT scans.

**3.2. Supernumerary teeth**

to a logical clinical outcome, as it provides superior information on root resorption.

canines.

122 Computed Tomography - Advanced Applications

Root resorption is a condition occurs in response to a variety of stimuli resulting in a loss of dentin, cementum or bone [36]. Panoramic radiographs have a week diagnostic efficacy in determining external root resorption. So, root resorption has traditionally been evaluated by periapical radiographs. Nevertheless, in recent years, it is suggested that CBCT can detect precise images of small root defects with a greater sensitivity and specificity compared to 2D radiographs [3, 24]. In a meta‐analysis, Yi et al. [38] reported that CBCT is superior to periapi‐ cal radiographs in the accuracy of diagnosing external root resorption. They emphasized that periapical radiographs provide limited information of external root resorption in the buccal and lingual root surface.

External root resorption of maxillary lateral incisor is a common finding that associates with canine impaction. Early diagnosis is difficult as it is asymptomatic and advanced root resorption makes the treatment planning more complex. In a study evaluating efficacy of CBCT for the diagnosis of root resorption associated with impacted canines, improved detection rates of root resorption (63%) were reported [39]. By using CBCT, it is possible to visualize of root resorptions on buccal and lingual surfaces. This might be critical for the extraction decision during treatment planning. In another study, it was suggested that the combination of thin slices and high resolution caused overestimation of the cavities for moderate root resorption cases [3].

The main problem is to decide how and when a clinician justify taking CBCT scan when a patient has undergone root resorption. Yi et al. [38] suggested that patients with clinically suspected root resorption be first evaluated by periapical radiographs. If positive results are obtained, for further examination, CBCT should be considered.

Alqerban et al. [10] reported that all CBCT systems used in their study showed high accuracy in the detection of root resorption, and there was no significant difference among CBCT systems in the detection of the severity of root resorption. Limitations of using CBCT for external root

**Figure 2.** Evaluation of position of a supernumerary tooth and impacted incisor and their relation with neighboring structures.

resorption are the detection of small resorptions in the apical third and the high dose of radia‐ tion required [3].

### **3.4. Evaluation of root angulation and length**

CBCT imaging becomes a preferred method for diagnosis by orthodontists because of its three dimensional rendering capability. Root position and morphology are critical issues for an orthodontist as it may affect the final occlusion. Root anatomy, such as short or dilacer‐ ated, is a determinant factor for the amount and direction of a tooth movement. Furthermore, because of the concerns about external root resorption, orthodontists need to get precise mea‐ surements of root angulation and length before treatment. Using CBCT images also provide detailed information about dysmorphic roots. Root positioning and morphology might be indicators of a disease. Of course, all root anomalies are not identical, but when supported with genetic testing, CBCT imaging will be helpful in interpreting anomalous root morphol‐ ogy in syndromic cases [40].

### **3.5. Tooth‐bone relationship**

In bimaxillary protrusion cases, Class 3 patients with an initial symphysis bone width, cases with preexisting periodontal disease, after maxillary expansion treatment, CBCT pro‐ vides valuable information about tooth‐bone relationships, and it might reduce the risk factor for dehiscence. While assessing deficiencies of buccolingual thickness in the alveolar ridge of patients subjected to critical tooth movement, high resolution and a limited FOV is recommended [41].

### **3.6. Cleft lip and palate (CLP) cases**

Patients with CLP are treated by interdisciplinary teams from infancy until adulthood. Several types of surgical procedures are used to reconstruct the anatomy of the alveolar ridge, dentofacial region, lips and nose. The SEDENTEXCT Consortium stated, in regard to the radiation dose, that "the application of CBCT in cleft lip and palate patients was found to be the simplest to support" in dentistry [42]. However, in a recent systematic review, it was suggested that further investigation is necessary to determine the influence of this new 3D facial imaging modality on treatment planning, treatment outcome and treatment evaluation.

The preoperative CBCT may provide reliable estimates on how much expansion and graft material will be needed, aid in appropriate selection of an autogenous graft donor site before surgery and enable the visualization of the three‐dimensional morphology of the bone bridge, the relationship between the bone bridge and roots of the neighboring teeth. For alveolar bone graft success, determination of the buccal‐palatal width of the bone in CLP cases, the use of CBCT is recommended [43] (**Figure 3**). Pharyngeal space, the results of bone grafting, and the effect of nasoalveolar molding can be evaluated with a post‐treatment CBCT.

**Figure 3.** Preoperative CBCT view of a CLP case showing the graft site.

resorption are the detection of small resorptions in the apical third and the high dose of radia‐

CBCT imaging becomes a preferred method for diagnosis by orthodontists because of its three dimensional rendering capability. Root position and morphology are critical issues for an orthodontist as it may affect the final occlusion. Root anatomy, such as short or dilacer‐ ated, is a determinant factor for the amount and direction of a tooth movement. Furthermore, because of the concerns about external root resorption, orthodontists need to get precise mea‐ surements of root angulation and length before treatment. Using CBCT images also provide detailed information about dysmorphic roots. Root positioning and morphology might be indicators of a disease. Of course, all root anomalies are not identical, but when supported with genetic testing, CBCT imaging will be helpful in interpreting anomalous root morphol‐

In bimaxillary protrusion cases, Class 3 patients with an initial symphysis bone width, cases with preexisting periodontal disease, after maxillary expansion treatment, CBCT pro‐ vides valuable information about tooth‐bone relationships, and it might reduce the risk factor for dehiscence. While assessing deficiencies of buccolingual thickness in the alveolar ridge of patients subjected to critical tooth movement, high resolution and a limited FOV

Patients with CLP are treated by interdisciplinary teams from infancy until adulthood. Several types of surgical procedures are used to reconstruct the anatomy of the alveolar ridge, dentofacial region, lips and nose. The SEDENTEXCT Consortium stated, in regard to the radiation dose, that "the application of CBCT in cleft lip and palate patients was found to be the simplest to support" in dentistry [42]. However, in a recent systematic review, it was suggested that further investigation is necessary to determine the influence of this new 3D facial imaging modality on treatment planning, treatment outcome and

The preoperative CBCT may provide reliable estimates on how much expansion and graft material will be needed, aid in appropriate selection of an autogenous graft donor site before surgery and enable the visualization of the three‐dimensional morphology of the bone bridge, the relationship between the bone bridge and roots of the neighboring teeth. For alveolar bone graft success, determination of the buccal‐palatal width of the bone in CLP cases, the use of CBCT is recommended [43] (**Figure 3**). Pharyngeal space, the results of bone grafting, and the effect of nasoalveolar molding can be evaluated with a

tion required [3].

ogy in syndromic cases [40].

**3.5. Tooth‐bone relationship**

is recommended [41].

treatment evaluation.

post‐treatment CBCT.

**3.6. Cleft lip and palate (CLP) cases**

**3.4. Evaluation of root angulation and length**

124 Computed Tomography - Advanced Applications

### **3.7. Temporomandibular joint (TMJ) morphology and pathology contributing to malocclusion**

The changes in the size, form and special and functional relationships of the TMJ compo‐ nents might cause pathological TMJ conditions. TMJ disorders which occurred during active growth period might alter jaw, tooth positions and occlusion. Even though signs and symp‐ toms of disturbances in the masticatory system are common, understanding the cause can be very complex. A proper diagnosis is possible, if only a through history and examination were achieved. Various types of imaging techniques can be used to gain additional informa‐ tion regarding the health and function of TMJs. CBCT is indicated for orthodontic cases that require analysis of TMJ bone components accompanied by signs and symptoms [44, 45]. One of the greatest advantages of CT scan is evaluating the condyle‐disk relationship [46]. In comparison with panoramic radiograph and linear tomography, CBCT proves more accurate in diagnosing erosion of the condyle [47]. Soft tissue imaging is possible, but bony tissues are best imaged with CT scans [48]. As magnetic resonance imaging enables visualizing the non‐mineralized soft tissues, it is preferable for the diagnosis of internal derangements of TMJ. However, it is not possible to observe dynamic joint movements.

Besides the evaluation of TMJ disorders, CBCT has been used to evaluate the condylar changes after orthodontic treatment. It allows volumetric evaluation of TMJ and provides better land‐ mark identification on curved surfaces like condyle. Literature review showed that CBCT evalu‐ ation was preferred to determine respond of TMJ to mandibular advancement [49] or extraction treatment [50] and effects of the distraction splint therapy in mandibular asymmetry cases.

### **3.8. Airway morphology and obstructive sleep apnea (OSA)**

Sleep‐disordered breathing is a spectrum of conditions with abnormal respiratory pattern, and OSA is the severe end of that spectrum. Orthodontics takes place in the management of OSA by using mandibular advancement appliances and by planning orthognathic surgery in these cases. It is also crucial to evaluate the dimensional changes in the nasopharyngeal area and airway obstruction in CLP [51]. Until recent years, lateral cephalometric radiography was used for the evaluation of the upper airway. But, changes which occur in the transverse dimension cannot be visualized. Three‐dimensional analysis and evaluation of airway have got a significant attention in the literature. CBCT allows orthodontists to measure cross‐sec‐ tional area, minimum cross section and total volume of the patient's airway accurately. Also, it has been used to investigate the effects of orthodontic treatments and orthognathic surgery on airway dimensions.

Studies of the upper airway based on CBCT scans are considered to be reliable in providing important information about the morphology of the pharyngeal airway; however, they have limitation in distinguishing different types of soft tissues [52]. Variations in airway dimen‐ sions and morphology due to patient's swallowing movement and head posture are also among the limitations of this technique [53].

### **3.9. Maxillary transverse dimension and maxillary expansion**

In the treatment of transverse maxillary deficiencies, it is important to assess transverse dimension as early as possible and accurately diagnose the need for transverse maxillary expansion using proper diagnostic tools. Before CBCT, post‐treatment skeletal changes on patients treated with RME were measured on dental casts, lateral and posterior‐anterior cephalometric and occlusal radiographs. Researches to date on rapid maxillary expansion have focused on determining treatment outcomes like dental tipping, alveolar bone bending, skeletal expansion and soft tissue changes, rather than the benefits of CBCT in diagnosis and treatment planning. Nowadays, it is claimed that CBCT images appear to be more reliable than posteroanterior cephalograms, offer an unobstructed view for the assessment of trans‐ versal intermaxillary discrepancies and provide much greater resolution and minimal image distortion [15]. However, the radiation dosage and its effect on growing patients must be taken into account.

The mid‐palatal suture becomes more fused after the completion of the adolescent growth spurt [54], as prediction of mid‐palatal suture maturation is possible by using CBCT [55]. It is a reliable diagnostic tool, while planning surgically assisted rapid maxillary expansion (SARME) in skeletally mature patients or using bone‐borne devices, which have recently gained popularity. It is possible to determine treatment outcomes of SARME and also permits the detection of the complications, such as tooth tilting of the anchoring teeth and bone fenes‐ tration due to periodontal stress [56].

### **3.10. Temporary anchorage device (TAD) placement**

In recent years, TADs are considered as a prerequisite for the resistance of unwanted tooth movements during the treatment of various orthodontic problems without patient compli‐ ance. The most common indications for treatment with TADs are molar protraction followed by indirect skeletal anchorage for space closure, intrusion of supraerupted teeth, intrusion of anterior to manage anterior open bite, anterior en‐masse retraction, molar uprighting, intrusion of maxillary cant, molar distalization, traction on impacted canine, and attachment for protraction facemask. CBCT images can be helpful to anchor the miniscrew and mini‐ plate securely in the surrounding bone and to visualize neighboring structures for avoiding damage or complications during TAD placement and be useful in identifying optimal site location (**Figure 4**).

these cases. It is also crucial to evaluate the dimensional changes in the nasopharyngeal area and airway obstruction in CLP [51]. Until recent years, lateral cephalometric radiography was used for the evaluation of the upper airway. But, changes which occur in the transverse dimension cannot be visualized. Three‐dimensional analysis and evaluation of airway have got a significant attention in the literature. CBCT allows orthodontists to measure cross‐sec‐ tional area, minimum cross section and total volume of the patient's airway accurately. Also, it has been used to investigate the effects of orthodontic treatments and orthognathic surgery

Studies of the upper airway based on CBCT scans are considered to be reliable in providing important information about the morphology of the pharyngeal airway; however, they have limitation in distinguishing different types of soft tissues [52]. Variations in airway dimen‐ sions and morphology due to patient's swallowing movement and head posture are also

In the treatment of transverse maxillary deficiencies, it is important to assess transverse dimension as early as possible and accurately diagnose the need for transverse maxillary expansion using proper diagnostic tools. Before CBCT, post‐treatment skeletal changes on patients treated with RME were measured on dental casts, lateral and posterior‐anterior cephalometric and occlusal radiographs. Researches to date on rapid maxillary expansion have focused on determining treatment outcomes like dental tipping, alveolar bone bending, skeletal expansion and soft tissue changes, rather than the benefits of CBCT in diagnosis and treatment planning. Nowadays, it is claimed that CBCT images appear to be more reliable than posteroanterior cephalograms, offer an unobstructed view for the assessment of trans‐ versal intermaxillary discrepancies and provide much greater resolution and minimal image distortion [15]. However, the radiation dosage and its effect on growing patients must be

The mid‐palatal suture becomes more fused after the completion of the adolescent growth spurt [54], as prediction of mid‐palatal suture maturation is possible by using CBCT [55]. It is a reliable diagnostic tool, while planning surgically assisted rapid maxillary expansion (SARME) in skeletally mature patients or using bone‐borne devices, which have recently gained popularity. It is possible to determine treatment outcomes of SARME and also permits the detection of the complications, such as tooth tilting of the anchoring teeth and bone fenes‐

In recent years, TADs are considered as a prerequisite for the resistance of unwanted tooth movements during the treatment of various orthodontic problems without patient compli‐ ance. The most common indications for treatment with TADs are molar protraction followed by indirect skeletal anchorage for space closure, intrusion of supraerupted teeth, intrusion of anterior to manage anterior open bite, anterior en‐masse retraction, molar uprighting,

on airway dimensions.

126 Computed Tomography - Advanced Applications

taken into account.

tration due to periodontal stress [56].

**3.10. Temporary anchorage device (TAD) placement**

among the limitations of this technique [53].

**3.9. Maxillary transverse dimension and maxillary expansion**

CBCT technology enables us to evaluate the interradicular distance and thickness, trans‐ verse bone thickness, bone density and thickness, cortical bone dimensions and quality. Even though anterior palate offers the greatest bone thickness, Holm et al. [57] recom‐ mended a CBCT evaluation for maximum screw length, as there is considerable varia‐ tion of bone thickness between individuals. Before placing a miniscrew by using CBCT, it is also possible to define even cranial and caudal boundaries, besides alveolar boundary conditions, and eliminate the risk of bone and root perforations. Surgical guides fabri‐ cated using CBCT images will help to avoid possible root and maxillary sinuses damage. Finite element analysis constructed using CBCT will also guide the evaluation of mechani‐ cal advantages or disadvantages of the orthodontic appliances with TADs by simulating stress distribution.

There are several factors that affect the stability and success rate of TADs. If cortical bone thick‐ ness is less than 1 mm, primary stability may not be achieved, and the TAD may loosen dur‐ ing orthodontic treatment [58]. Evaluation of cortical bone quantity and quality is also critical for long‐term stability. With finite element analysis, it has been shown that root contact is also one of the factors that can cause loss of miniscrew stability [59]. The information gathered from CBCT will be determinant for some of these factors, such as the dimension and insertion

**Figure 4.** Planning and preparation of TAD (zygomatic skeletal anchorage) on a 3D model obtained from CBCT before surgery.

angle of the miniscrew, the insertion procedure, the depth of the screw insertion and insertion torque [38, 57, 60].

In some cases, routine panoramic, lateral and frontal cephalometric radiographs may not pro‐ vide all information needed to optimize the location of a miniscrew placement. However, it should be kept in mind that in regions with a high bone quality, such as paramedian palate and palatal region, lateral cephalometric radiographs are usable to determine the location of TADs. Therefore, it is not necessary to take a CBCT in all cases [61].

It is recommended to use the smallest possible FOV unless the CBCT is needed for the diag‐ nosis of another condition in which case a large FOV may be preferred [60].

### **3.11. Dentofacial deformities and craniofacial anomalies**

Evaluation of changes in the craniofacial region during growth and with treatment using lateral cephalograms makes a great contribution to the science of orthodontics. However, in recent years, researches discussed the validity of evaluating a 3D craniofacial structure in a 2D plane. CBCT imaging can provide valuable information about dentofacial deformities and craniofacial anomalies, like facial asymmetry which affects three dimensions of the face, and it can be used to simulate virtual treatment plans for orthopedic corrections, orthog‐ nathic surgeries and distraction osteogenesis. By capturing images and analyzing the cra‐ niofacial hard and soft tissues and by generating virtual patient models, CBCT imaging permits the clinicians to reposition and reconstruct craniofacial structures (**Figure 5a**, **b**).

Several studies were conducted to determine reference planes, to develop cephalometric analysis, to evaluate the accuracy of these measurements, to establish the mean normality val‐ ues and to assess the differences of gender and ethnic groups for 3D evaluations [62]. Besides morphological analysis, these images are used to evaluate the spatial relationship of the neighboring structures. CBCT technology enables carrying out the model surgery. So, com‐ puter assisted orthognathic surgery permits the design and fabrication of the occlusal surgi‐ cal splints. By using virtual models, constructing anatomically grafts and correct replacement can be achieved (**Figure 6**). The data obtained from CBCT provide a better prediction of soft tissue response to the changes in the hard tissue after orthognathic surgery [63]. In the litera‐ ture, CBCT is recommended for the assessment of preoperative orthodontic decompensation of maxillary and mandibular incisors [64]. This is an additional information from CBCT that is taken for orthognathic surgery planning, and it could not be one of the main purpose of using CBCT. Furthermore, CBCT proves a good method to assess TMJ after orthognathic surgery, particularly when there is considerable potential for resorption of the condyle [14].

#### **3.12. Treatment outcomes**

Taking CBCT at the end of orthodontic treatment is a controversial issue. However, it must be taken into consideration that studies on response to treatment can help elucidate clinical questions on variability of outcomes of treatment. There are studies assessing treatment

**Figure 5.** (a) 3D view of a case with Golden Haar syndrome. Note the asymmetric growth of left and right condyles. (b) 3D evaluation of mandible and condyles in this case.

outcomes of orthognathic surgery, maxillary expansion, bone grafting and several orthope‐ dic appliances. A review of literature showed that jaw and teeth relationships, soft tissue, hyoid bone position, pharyngeal airway dimensions and morphology were evaluated after orthodontic and surgical treatments. To facilitate the evaluation of treatment outcomes, superimposition methods for CBCT images were also offered [28].

### **3.13. Evaluation of cervical vertebral maturation (CVM)**

angle of the miniscrew, the insertion procedure, the depth of the screw insertion and insertion

In some cases, routine panoramic, lateral and frontal cephalometric radiographs may not pro‐ vide all information needed to optimize the location of a miniscrew placement. However, it should be kept in mind that in regions with a high bone quality, such as paramedian palate and palatal region, lateral cephalometric radiographs are usable to determine the location of

It is recommended to use the smallest possible FOV unless the CBCT is needed for the diag‐

Evaluation of changes in the craniofacial region during growth and with treatment using lateral cephalograms makes a great contribution to the science of orthodontics. However, in recent years, researches discussed the validity of evaluating a 3D craniofacial structure in a 2D plane. CBCT imaging can provide valuable information about dentofacial deformities and craniofacial anomalies, like facial asymmetry which affects three dimensions of the face, and it can be used to simulate virtual treatment plans for orthopedic corrections, orthog‐ nathic surgeries and distraction osteogenesis. By capturing images and analyzing the cra‐ niofacial hard and soft tissues and by generating virtual patient models, CBCT imaging permits the clinicians to reposition and reconstruct craniofacial structures (**Figure 5a**, **b**).

Several studies were conducted to determine reference planes, to develop cephalometric analysis, to evaluate the accuracy of these measurements, to establish the mean normality val‐ ues and to assess the differences of gender and ethnic groups for 3D evaluations [62]. Besides morphological analysis, these images are used to evaluate the spatial relationship of the neighboring structures. CBCT technology enables carrying out the model surgery. So, com‐ puter assisted orthognathic surgery permits the design and fabrication of the occlusal surgi‐ cal splints. By using virtual models, constructing anatomically grafts and correct replacement can be achieved (**Figure 6**). The data obtained from CBCT provide a better prediction of soft tissue response to the changes in the hard tissue after orthognathic surgery [63]. In the litera‐ ture, CBCT is recommended for the assessment of preoperative orthodontic decompensation of maxillary and mandibular incisors [64]. This is an additional information from CBCT that is taken for orthognathic surgery planning, and it could not be one of the main purpose of using CBCT. Furthermore, CBCT proves a good method to assess TMJ after orthognathic surgery, particularly when there is considerable potential for resorption of the condyle [14].

Taking CBCT at the end of orthodontic treatment is a controversial issue. However, it must be taken into consideration that studies on response to treatment can help elucidate clinical questions on variability of outcomes of treatment. There are studies assessing treatment

TADs. Therefore, it is not necessary to take a CBCT in all cases [61].

**3.11. Dentofacial deformities and craniofacial anomalies**

nosis of another condition in which case a large FOV may be preferred [60].

torque [38, 57, 60].

128 Computed Tomography - Advanced Applications

**3.12. Treatment outcomes**

Skeletal maturation of patients is an important factor while planning orthodontic treatment. Hand‐wrist and CVM methods were used for assessing the adolescent growth peak. It is sug‐ gested that the CBCT images may be useful for estimates of skeletal maturation, although they should not be used solely for that purpose [65]. Shim et al. [66] claimed that the esti‐

**Figure 6.** Presurgical 3D model of a case with Crouzon syndrome obtained from CBCT.

mate of maturation stages of the cervical vertebrae on CBCT provided a reliable evaluation of pubertal growth support and strongly positive correlations with lateral cephalograms and hand‐wrist radiographs.

### **4. Radiation dose**

Radiation dose depends on the CBCT scanner's specifications, milliampere setting, peak kilo‐ voltage (kVp), voxel size, sensor sensitivity and number of images obtained, the time of scan‐ ning, and FOV. It is recommended to apply the 3D evaluation when the use of CBCT can be justified. Clinicians should always keep in mind that the radiation exposure to a human being should be kept "As Low As Reasonably Achievable" (ALARA) principle.

SEDENTEXCT project guidelines include a variety of topics, like justification, referral crite‐ ria, optimization, training, quality assurance and staff protection aspects [67]. Justification of using CBCT in dentistry can be considered if only a patient history and clinical infor‐ mation are available, if additional new information is expected, and if 2D radiographs are inadequate for diagnosis. The orthodontist should weigh the potential benefits of a CBCT against the chance of causing cancer for each patient. The chance may be small, but it is never negligible.

To reduce the patient dose, the smallest available volume size should be preferred. kVp and mAs of CBCT used in dental and maxillofacial region vary in a wide range and patients' doses varies considerably. It is recommended to standardize exposure parameters in dental and maxillofacial CBCT for each imaging task [68]. Gamache et al. [7] suggested that the total radiation exposure from CBCT scans can be reduced by while maintaining adequate image quality using low kV and moderate‐to‐high mA settings rather than the manufacturer‐recom‐ mended settings.

Voxel size should be determined according to the purpose of the exam. When voxel dimen‐ sion decreases, a better spatial resolution will be achieved, but the radiation dose will be increased [70]. Voxel sizes of 0.3–0.4 mm should be preferred if there is no need for a high level of detail [41].

Using child dose is offered because effective doses are higher compared with adults if expo‐ sure factors are not adapted. In a study on estimation of pediatric organ and effective doses from dental CBCT in 2012, it was reported that the average effective doses to the 10‐year‐old and adolescent phantoms were 116 and 79 mSv, respectively, which are similar to adult doses. So, the authors concluded that dental CBCT examinations on children should be fully justi‐ fied over conventional X‐ray imaging due to the higher radiosensitivity of children and that dose optimization by FOV collimation is particularly important in young children [69]. FOV should be restricted as much as possible [42]. So, the examination should include only the areas of interest in order to minimize radiation dose and ALARA principle must be followed. Repeated CBCT examinations should be avoided. The patient must be informed, and consent of the patient or parents must be obtained.

Technical properties of CBCT units were given inadequately in several studies. To make a comparison based on effective dose between studies, these properties must be reported and more evidence base studies on effective dose and image quality relation are still needed [70].

### **5. Future of CBCT in orthodontics**

mate of maturation stages of the cervical vertebrae on CBCT provided a reliable evaluation of pubertal growth support and strongly positive correlations with lateral cephalograms and

Radiation dose depends on the CBCT scanner's specifications, milliampere setting, peak kilo‐ voltage (kVp), voxel size, sensor sensitivity and number of images obtained, the time of scan‐ ning, and FOV. It is recommended to apply the 3D evaluation when the use of CBCT can be justified. Clinicians should always keep in mind that the radiation exposure to a human being

SEDENTEXCT project guidelines include a variety of topics, like justification, referral crite‐ ria, optimization, training, quality assurance and staff protection aspects [67]. Justification

should be kept "As Low As Reasonably Achievable" (ALARA) principle.

**Figure 6.** Presurgical 3D model of a case with Crouzon syndrome obtained from CBCT.

hand‐wrist radiographs.

130 Computed Tomography - Advanced Applications

**4. Radiation dose**

Further research‐based technological developments are needed to achieve CBCT imaging, which is cost‐effective, more precise on landmark identification and providing more accurate image quality with reduced radiation dose. By technological evolution and innovation of this technique, indications and the usage of CBCT in orthodontics will advance in the future. Future investigations are needed to investigate the dose levels for pediatric imaging protocols and to assess the use of a thyroid collar as a dose reduction technique.

### **6. Conclusions**

In recent years, the use of CBCT in orthodontics has gained popularity and preferred as an imaging method by many clinicians for diagnosis and treatment planning. In this chapter, the indications and usage of CBCT in orthodontics are summarized. Clinicians should have comprehensive knowledge about advantages, disadvantages, limitations and potential risks due to increased radiation dose before deciding to use CBCT. Evidence‐based studies are still needed whether using CBCT has any effect on clinical decision and lead to an improvement in treatment outcome.

### **Acknowledgements**

We like to thank for their valuable contributions Dr. Sema Yuksel, Dr. Neslihan Ucuncu, Dr. Nilufer Darendeliler, Dr. Erdal Bozkaya, Dr.Secil Acar, Dr. Gülce Tosun who shared 3D views of their cases.

### **Author details**

Emine Kaygısız\* and Tuba Tortop

\*Address all correspondence to: dt.emineulug@mynet.com

Faculty of Dentistry, Department of Orthodontics, Gazi University, Ankara, Turkey

### **References**


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**6. Conclusions**

132 Computed Tomography - Advanced Applications

in treatment outcome.

**Acknowledgements**

of their cases.

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**Author details**

Emine Kaygısız\* and Tuba Tortop

\*Address all correspondence to: dt.emineulug@mynet.com

In recent years, the use of CBCT in orthodontics has gained popularity and preferred as an imaging method by many clinicians for diagnosis and treatment planning. In this chapter, the indications and usage of CBCT in orthodontics are summarized. Clinicians should have comprehensive knowledge about advantages, disadvantages, limitations and potential risks due to increased radiation dose before deciding to use CBCT. Evidence‐based studies are still needed whether using CBCT has any effect on clinical decision and lead to an improvement

We like to thank for their valuable contributions Dr. Sema Yuksel, Dr. Neslihan Ucuncu, Dr. Nilufer Darendeliler, Dr. Erdal Bozkaya, Dr.Secil Acar, Dr. Gülce Tosun who shared 3D views

Faculty of Dentistry, Department of Orthodontics, Gazi University, Ankara, Turkey

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## **Cone-Beam Computed Tomography for Oral and Maxillofacial Imaging**

Ufuk Tatli and Burcu Evlice

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138 Computed Tomography - Advanced Applications

2015;**88**:20140658

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69282

#### **Abstract**

The invention of computed tomography (CT) technique revolutionized diagnostic imaging. Compared to conventional X-ray imaging procedures, CT involves higher radiation doses. Recently, cone-beam CT (CBCT) specifically designed for maxillofacial imaging was introduced. CBCT technique is based on a cone-shaped X-ray beam centered on a twodimensional (2D) detector. The detector system performs one rotation around the patient, producing a series of 2D images which are then reconstructed in a 3D data set. The contemporary knowledge regarding CBCT and its proper application guides the practitioner for improvement in diagnostic purposes and treatment planning. The aim of this chapter is to focus on the details, advantages, drawbacks, and clinical applications of CBCT as a headmost CT imaging technique in the oral and maxillofacial (OMF) region. The main clinical applications of CBCT in the OMF region are dentistry including dentoalveolar and maxillofacial surgery, orthodontics, endodontics, and periodontics; and otolaryngology. The aforementioned clinical use of CBCT was described in detail with illustrated sample cases. In most of the cases in OMF region, CBCT takes the place of multi-slice CT. Thus, clinicians should know the clinical applications and capabilities of CBCT technique with its drawbacks.

**Keywords:** cone-beam computed tomography, dentistry, maxillofacial imaging, maxillofacial surgery, otolaryngology

### **1. Introduction**

Accurate diagnostic imaging is a key factor for diagnosis and treatment planning. The invention of computed tomography (CT) technique revolutionized diagnostic imaging. Since the inception of CT in the 1970s, it has become one of the commonly used imaging methods [1]. Threedimensional (3D) imaging provided by CT technology gives the opportunity to the clinician to examine the oral and maxillofacial (OMF) region without superimposition and distortion of the

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

image. Compared to conventional 2D imaging procedures, CT involves higher radiation doses. Recently, cone-beam computed tomography (CBCT) specifically designed for maxillofacial imaging was introduced to offset some of the limitations of conventional CT scanning devices [2].

The contemporary knowledge regarding CBCT and its proper application guides the practitioner for improvement in diagnostic purposes and treatment planning. The aim of this chapter is to focus on the technical features, advantages, drawbacks, limits, and clinical applications of CBCT as a headmost CT imaging technique in the OMF region.

### **2. Cone-beam technique**

The CBCT scanners for maxillofacial region were introduced in the 1990s independently in Japan [3] and in Italy [4]. Although it has been given several names including dental volumetric tomography (DVT), cone-beam volumetric tomography (CBVT), dental computed tomography (DCT), and cone-beam imaging (CBI), the most preferred name is cone-beam computed tomography (CBCT) [5].

CBCT imaging is performed by using a rotating gantry to which an X-ray source and detector are fixed. Cone-beam machines radiate an X-ray beam shaped liked a cone or pyramid, rather than a fan, as in conventional CT machines. The X-ray source and detector rotate around a rotation abutment fixed within the center of the region of interest. The beam exiting the patient is captured on a 2D planar detector, usually an amorphous silicon flat panel or sometimes an image intensifier/charge coupled device (CCD) detector. During the rotation, multiple consecutive planar projection images of the field of view (FOV) are acquired in a complete, or sometimes partial, arc. This procedure varies from a traditional medical CT, which uses a fanshaped X-ray beam in a helical progression to obtain individual image slices of the FOV and then heaps the slices to get a 3D representation. Each slice requires a separate scan and separate 2D reconstruction. Because CBCT exposure combines the whole FOV, only one rotational turn of the gantry is necessary to acquire enough data for image reconstruction [6, 7]. A cone-beam reconstruction process creates a 3D matrix that can be viewed as a series of 2D cross-sectional images—axial, sagittal, and coronal views. From this data set, the operator can also extract thick or thin, planar or curved reconstructions in any orientation. Axial planes are a series of slices from top to bottom in the volume. Sagittal planes are a series of 2D slices from left to right, and coronal planes are a series of 2D slices from anterior to posterior. In a multi-planar reformation (MPR) window, these three orthogonal planar views are related through intersection lines or crosshairs, allowing for straightforward orientation and navigation (**Figure 1**).

The dose associated with each scan is affected by a number of scan parameters selected by the practitioner, either manually or through preset exposure protocols. For most CBCT systems, the kVp is fixed, and the tube current (mA) and exposure time (s) can be varied depending on the desired image quality and patient size. After reconstruction, CBCT images can be manipulated in different ways to optimize the visualization of anatomical structures and lesions and to isolate certain parts of the image. Basic filtering can also be applied, both during and after reconstruction, in order to smooth or sharpen the image [8]. CBCT has some advantages and disadvantages over conventional CT. These items are summarized below [9–14].

Cone-Beam Computed Tomography for Oral and Maxillofacial Imaging http://dx.doi.org/10.5772/intechopen.69282 141

**Figure 1.** The example of multi-planar CBCT images including coronal, sagittal, axial, and 3D views.

#### **2.1. Advantages of CBCT over conventional CT**


image. Compared to conventional 2D imaging procedures, CT involves higher radiation doses. Recently, cone-beam computed tomography (CBCT) specifically designed for maxillofacial imaging was introduced to offset some of the limitations of conventional CT scanning devices [2]. The contemporary knowledge regarding CBCT and its proper application guides the practitioner for improvement in diagnostic purposes and treatment planning. The aim of this chapter is to focus on the technical features, advantages, drawbacks, limits, and clinical applications

The CBCT scanners for maxillofacial region were introduced in the 1990s independently in Japan [3] and in Italy [4]. Although it has been given several names including dental volumetric tomography (DVT), cone-beam volumetric tomography (CBVT), dental computed tomography (DCT), and cone-beam imaging (CBI), the most preferred name is cone-beam

CBCT imaging is performed by using a rotating gantry to which an X-ray source and detector are fixed. Cone-beam machines radiate an X-ray beam shaped liked a cone or pyramid, rather than a fan, as in conventional CT machines. The X-ray source and detector rotate around a rotation abutment fixed within the center of the region of interest. The beam exiting the patient is captured on a 2D planar detector, usually an amorphous silicon flat panel or sometimes an image intensifier/charge coupled device (CCD) detector. During the rotation, multiple consecutive planar projection images of the field of view (FOV) are acquired in a complete, or sometimes partial, arc. This procedure varies from a traditional medical CT, which uses a fanshaped X-ray beam in a helical progression to obtain individual image slices of the FOV and then heaps the slices to get a 3D representation. Each slice requires a separate scan and separate 2D reconstruction. Because CBCT exposure combines the whole FOV, only one rotational turn of the gantry is necessary to acquire enough data for image reconstruction [6, 7]. A cone-beam reconstruction process creates a 3D matrix that can be viewed as a series of 2D cross-sectional images—axial, sagittal, and coronal views. From this data set, the operator can also extract thick or thin, planar or curved reconstructions in any orientation. Axial planes are a series of slices from top to bottom in the volume. Sagittal planes are a series of 2D slices from left to right, and coronal planes are a series of 2D slices from anterior to posterior. In a multi-planar reformation (MPR) window, these three orthogonal planar views are related through intersection lines or crosshairs, allowing for straightforward orientation and navigation (**Figure 1**).

The dose associated with each scan is affected by a number of scan parameters selected by the practitioner, either manually or through preset exposure protocols. For most CBCT systems, the kVp is fixed, and the tube current (mA) and exposure time (s) can be varied depending on the desired image quality and patient size. After reconstruction, CBCT images can be manipulated in different ways to optimize the visualization of anatomical structures and lesions and to isolate certain parts of the image. Basic filtering can also be applied, both during and after reconstruction, in order to smooth or sharpen the image [8]. CBCT has some advantages and

disadvantages over conventional CT. These items are summarized below [9–14].

of CBCT as a headmost CT imaging technique in the OMF region.

**2. Cone-beam technique**

140 Computed Tomography - Advanced Applications

computed tomography (CBCT) [5].


#### **2.2. Disadvantages of CBCT over conventional CT**


**Figure 2.** The example of CBCT imaging of an alveolar cleft case showing only the region of interest in order to reduce radiation exposure.


According to literature, the subjective image quality was lower on older CBCT units compared to multi-slice CT [15]. However, recent CBCT units with higher resolution showed opposite results [16]. Although new CBCT scanners with flat panel detectors seem to be less prone to metal artifacts, an important problem including susceptibility to movement artifacts still remains [9]. The effective radiation doses for various CBCT devices range from 52 to 1025 micro-sieverts [5]. It was reported that 3D volumetric images obtained with CBCT technology involved up to four times less radiation than conventional CT [17]. Although CBCT requires lower radiation doses compared to CT imaging, the aforementioned radiation doses are still higher than 2D imaging. In order to protect patients and staff during acquisition of images, the selection criteria of CBCT examination should weigh potential benefits against the risks associated with radiation dose. For this purpose, appropriate clinical usage, protective shielding, and the smallest FOV for diagnostic purposes should be obtained (**Figure 2**).

### **3. Applications of CBCT in oral and maxillofacial region**

CBCT is used in all medical and dental disciplines practicing in OMF region, whereas early CBCT devices were dedicated to implantology and dental imaging; nowadays, applications include the whole face and skull. Image analysis function obtains quantifiable accurate data from the image for diagnostic and scientific purposes. Linear, curved, and angular measurements, area and volume calculation, and densitometric analysis can be performed [13, 18–20]. The main clinical applications of CBCT in the OMF region are: dentoalveolar and maxillofacial surgery, maxillofacial pathology, orthodontics, implantology, endodontics, periodontics, and otolaryngology. The CBCT technology can also be used in forensic medicine. The clinical use of CBCT will be reviewed below with illustrated sample cases:

### **3.1. Oral and maxillofacial surgery**

The OMF surgery is the main discipline which uses the CBCT technology. In a literature review, it was reported that 41% of the scientific papers related to the clinical applications of CBCT dealt with the use for maxillofacial surgery [9]. The main topics may be summarized as dental implantology, impacted and supernumerary tooth, OMF pathology, maxillofacial trauma, temporomandibular joint (TMJ) disorders, dentofacial discrepancies, and cleft palate.

#### *3.1.1. Dental implantology*

• Bone density values without a linear correlation between different devices.

and the smallest FOV for diagnostic purposes should be obtained (**Figure 2**).

**3. Applications of CBCT in oral and maxillofacial region**

tal restorations and implants.

142 Computed Tomography - Advanced Applications

radiation exposure.

• Reduced image quality in regions close to high-density neighboring structures such as den-

**Figure 2.** The example of CBCT imaging of an alveolar cleft case showing only the region of interest in order to reduce

According to literature, the subjective image quality was lower on older CBCT units compared to multi-slice CT [15]. However, recent CBCT units with higher resolution showed opposite results [16]. Although new CBCT scanners with flat panel detectors seem to be less prone to metal artifacts, an important problem including susceptibility to movement artifacts still remains [9]. The effective radiation doses for various CBCT devices range from 52 to 1025 micro-sieverts [5]. It was reported that 3D volumetric images obtained with CBCT technology involved up to four times less radiation than conventional CT [17]. Although CBCT requires lower radiation doses compared to CT imaging, the aforementioned radiation doses are still higher than 2D imaging. In order to protect patients and staff during acquisition of images, the selection criteria of CBCT examination should weigh potential benefits against the risks associated with radiation dose. For this purpose, appropriate clinical usage, protective shielding,

CBCT is used in all medical and dental disciplines practicing in OMF region, whereas early CBCT devices were dedicated to implantology and dental imaging; nowadays, applications include the whole face and skull. Image analysis function obtains quantifiable accurate data from the image for diagnostic and scientific purposes. Linear, curved, and angular During the preoperative planning of dental implant treatment, radiographic methods for assessment of bone quality and quantity are frequently used. For 2D assessment, orthopantomography (OPG) is frequently used. The American Association of Oral and Maxillofacial Radiology recommends cross-sectional views for evaluation of a potential implant site [14]. CBCT provides the 3D visualization of the alveolar bone height, width, and thickness, and spatial proximity of inferior alveolar and incisive canals, maxillary sinus, and nasal cavity (**Figure 3**). It is the contemporary method used for planning dental implant surgery and bone augmentation

**Figure 3.** The example of CBCT imaging including cross-sectional view showing the alveolar bone height and width, and localization of maxillary sinus and mental nerve.

procedures (**Figure 4**). As shown in our previous clinical study, accurate measurements can be performed on CBCT images for diagnosis, treatment planning, and evaluation of treatment results of bone augmentation and dental implants [21]. The CBCT images are free from distortion; however, errors in patient positioning may lead to inaccurate measurements which may

**Figure 4.** The CBCT imaging of a patient with atrophic maxilla who needs bone augmentation and dental implant treatment. **a.** Before bone augmentation. **b.** After bone augmentation (from iliac crest).

cause damage to anatomical structures. The success of dental implant treatment is influenced by both the quality and quantity of available bone for implant placement. During the past few years, the concept of using CT-derived Hounsfield unit (HU) values had increasing popularity for quantitative assessment of bone density [22, 23]. However, patients are exposed to high radiation during CT scanning. Besides quantitative assessment of bone, CBCT can also be used for evaluation of bone quality (**Figure 5**). In recent studies, significant correlations between the density values of CBCT and HU values of CT were reported [24, 25]. In contrast, controversial results concerning the assessment of bone density using CBCT were also reported in literature [13, 26]. In our previous clinical studies, we observed significant correlation between CBCTderived bone density and dental implant stability parameters including insertion torque value and resonance frequency analysis [27, 28]. Thus, it seems to be possible to predict bone density, initial implant stability, and possibility of immediate or early loading using CBCT scan prior to implant surgery.

Moreover, it is also possible to perform navigation-guided implant surgery by using specific software and CBCT imaging. The 3D specific navigation system provides surgeons an additional planning tool during implant surgery, offering instant and continuous visualization of drill tip and angle and their relations with neighboring vital structures that have to be respected in the three spatial planes in CBCT images. With the guidance of the dynamic navigation system, surgeon can monitor the 360° view of the relationship among implant drill, inferior alveolar nerve, maxillary sinus, nasal cavity, and buccal and lingual alveolar bone plates during surgery (**Figure 6**).

### *3.1.2. Impacted and supernumerary tooth*

procedures (**Figure 4**). As shown in our previous clinical study, accurate measurements can be performed on CBCT images for diagnosis, treatment planning, and evaluation of treatment results of bone augmentation and dental implants [21]. The CBCT images are free from distortion; however, errors in patient positioning may lead to inaccurate measurements which may

144 Computed Tomography - Advanced Applications

**Figure 4.** The CBCT imaging of a patient with atrophic maxilla who needs bone augmentation and dental implant

treatment. **a.** Before bone augmentation. **b.** After bone augmentation (from iliac crest).

The CBCT is also used for presurgical evaluation of impacted teeth, supernumerary teeth, and their relations with neighboring anatomic structures (adjacent teeth, inferior alveolar nerve,

**Figure 5.** The example of cross-sectional CBCT imaging used to calculate bone density of the designated implant region.

**Figure 6.** CBCT-based navigation-guided dental implant surgery. **a.** Clinical view. **b.** Software view (by the courtesy of Dr Yakup Üstün).

mental nerve, and maxillary sinus). Thus, clinician is able to plan the surgery and inform the patients about possible risks (**Figure 7**). In a recent clinical study, Jawad et al. reported that CBCT provided improved detection rates (63% versus 45% for plain radiographs) of root resorption associated with impacted canines. The authors also introduced a new root resorption scale for CBCT imaging [29].

#### *3.1.3. Oral and maxillofacial pathology*

**Figure 6.** CBCT-based navigation-guided dental implant surgery. **a.** Clinical view. **b.** Software view (by the courtesy of

Dr Yakup Üstün).

146 Computed Tomography - Advanced Applications

All kinds of pathologic lesions which affect bone tissue in the OMF region including infection, cysts, tumors, and osteonecrosis can be monitored by CBCT imaging. The CBCT assessment provides maxillofacial surgeon to visualize the accurate localization of pathologic entity and its relation with adjacent vital structures in multi-planar view (**Figure 8**). For medication-related osteonecrosis of the jaws (MRONJ) lesions, the innovative use of routine tumor-surveillance imaging in combination with CBCT imaging was described to provide a high-resolution 3D analysis [30]. The authors interpreted functional imaging information by fusing positron emission tomography/computed tomography (PET/CT) and single-photon emission computed tomography/computed tomography (SPECT/CT) data with CBCT data. Hence, the authors stated that this new composite image analysis, if validated, will facilitate surgical planning by demarcating MRONJ area. The 3D model preparation and adaptation of the reconstruction plates to the jawbone before surgery can also be possible with CBCT imaging for maxillofacial reconstruction patients (**Figure 9**).

**Figure 7.** The example of CBC imaging showing the inferior alveolar nerve and its relation with mandibular impacted third molar tooth.

**Figure 8.** The example of CBCT imaging of a pathologic lesion located in the mandible (reparative giant cell granuloma).

#### *3.1.4. Maxillofacial traumatology*

Maxillofacial trauma patients can be assessed with CBCT to plan appropriate treatment method (**Figure 10**). The diagnostic performance of CBCT in detecting orbital floor fractures was reported to be better than ultrasonography. Moreover, it was also reported that CBCT could be used in detecting fractures as a reliable surrogate to CT [31]. The CBCT technology

**Figure 9.** (a) The CBCT imaging of a patient with pathologic mandible fracture due to MRONJ. (b) The CBCT-based 3D model of the patient. Note that bending and adaptation of the titanium plate to the model before surgery can facilitate reconstructive procedures.

**Figure 10.** The example of CBCT imaging of a patient with mandibular left parasymphysis and condyle fracture.

can also be used in combination with specific computer software for preoperative virtual planning and fabrication of patient-specific reconstruction plate for mandibular fractures [32]. When CBCT and multi-detector CT were compared in diagnostic imaging of midface, it was concluded that CBCT provided better image quality at lower doses, comparable image quality at higher doses, and superior spatial resolution in standard- and reduced-dose settings [33]. However, in another recent study, it was concluded that CBCT was not optimal for postoperative facial imaging compared to multi-slice CT in terms of visualization of maxillofacial bony structures in the vicinity of osteosynthesis materials [34].

#### *3.1.5. Temporomandibular joint disorders*

*3.1.4. Maxillofacial traumatology*

148 Computed Tomography - Advanced Applications

reconstructive procedures.

Maxillofacial trauma patients can be assessed with CBCT to plan appropriate treatment method (**Figure 10**). The diagnostic performance of CBCT in detecting orbital floor fractures was reported to be better than ultrasonography. Moreover, it was also reported that CBCT could be used in detecting fractures as a reliable surrogate to CT [31]. The CBCT technology

**Figure 9.** (a) The CBCT imaging of a patient with pathologic mandible fracture due to MRONJ. (b) The CBCT-based 3D model of the patient. Note that bending and adaptation of the titanium plate to the model before surgery can facilitate

**Figure 8.** The example of CBCT imaging of a pathologic lesion located in the mandible (reparative giant cell granuloma).

Temporomandibular disorders associated with degenerative pathologies or abnormalities in the bony structures of condyle, glenoid fossa, and articular eminence such as cortical erosion, articular surface flattening, osteophytes, condiylar hyper-, hypo-, or aplasia, ankylosis, and coronoid process hyperplasia can be visualized with CBCT [9–11]. A CBCT imaging for TMJ complex requires less time and lower radiation doses, it provides the multi-planar views for both TMJs from a single 360° rotation scan, and it simplifies positioning of patient [11]. The linear, angular, and volumetric measurements can also be performed with CBCT imaging software for research purposes. The image-guided puncture technique for TMJ using CBCT can also be used to determine the optimum angle and distance in order to prevent middle cranial fossa damage [35]. These measurements can be used to produce stereographic models and custom-made TMJ prosthesis. The CBCT imaging can only be used to assess the bony structures of TMJ. In general, it is not the imaging of choice for TMJ disorders including myofacial pain dysfunction or internal derangements. The examples of CBCT images acquired for TMJ disorders are shown in **Figures 11**–**13**.

### *3.1.6. Dentomaxillofacial discrepancies and cleft palate*

The growth abnormalities of maxillofacial bones can be assessed by CBCT imaging (**Figure 14**). The treatment planning and success of the surgical treatments of alveolar cleft patients can be assessed with CBCT imaging (**Figure 15**). As reported in our previous study, it is possible to compare the bone density values of the cleft and non-cleft sites to evaluate the success of alveolar cleft repair using CBCT technology [36]. Moreover, 3D measurement of cleft area including volume of bone defect and outcomes after alveolar grafting in cleft lip and palate patients can also be assessed by CBCT imaging. The dentofacial discrepancies can be visualized, and virtual planning of orthognathic surgeries can be performed with CBCT imaging and special software. Recently, a novel technique for splintless orthognathic surgery, using CBCT imaging with computer-aided design/computer-aided manufacturing (CAD/CAM) technology and virtual planning software, was introduced [37].

The growth abnormalities of head and neck bones can also be scanned using CBCT technology (**Figure 16**). As reported in our previous study, visualization of the styloid process elongation in detail including linear and angular measurements can also be performed with CBCT imaging [18].

**Figure 11.** The multi-planar CBCT imaging of a patient with right TMJ ankylosis.

and custom-made TMJ prosthesis. The CBCT imaging can only be used to assess the bony structures of TMJ. In general, it is not the imaging of choice for TMJ disorders including myofacial pain dysfunction or internal derangements. The examples of CBCT images acquired for

The growth abnormalities of maxillofacial bones can be assessed by CBCT imaging (**Figure 14**). The treatment planning and success of the surgical treatments of alveolar cleft patients can be assessed with CBCT imaging (**Figure 15**). As reported in our previous study, it is possible to compare the bone density values of the cleft and non-cleft sites to evaluate the success of alveolar cleft repair using CBCT technology [36]. Moreover, 3D measurement of cleft area including volume of bone defect and outcomes after alveolar grafting in cleft lip and palate patients can also be assessed by CBCT imaging. The dentofacial discrepancies can be visualized, and virtual planning of orthognathic surgeries can be performed with CBCT imaging and special software. Recently, a novel technique for splintless orthognathic surgery, using CBCT imaging with computer-aided design/computer-aided manufacturing (CAD/CAM) technol-

The growth abnormalities of head and neck bones can also be scanned using CBCT technology (**Figure 16**). As reported in our previous study, visualization of the styloid process elongation in detail including linear and angular measurements can also be performed with

TMJ disorders are shown in **Figures 11**–**13**.

150 Computed Tomography - Advanced Applications

*3.1.6. Dentomaxillofacial discrepancies and cleft palate*

ogy and virtual planning software, was introduced [37].

**Figure 11.** The multi-planar CBCT imaging of a patient with right TMJ ankylosis.

CBCT imaging [18].

**Figure 12.** (a) The 3D CBCT views of a patient with bilateral coronoid process hyperplasia before and after coronoidectomy surgery (arrows). (b) The resected bone pieces of coronoid process.

**Figure 13.** The CBCT imaging of a patient with right mandibular condylar hyperplasia (red arrows).

**Figure 14.** The 3D CBCT imaging of a patient with mandibular asymmetry who needs orthognathic surgery.

Cone-Beam Computed Tomography for Oral and Maxillofacial Imaging http://dx.doi.org/10.5772/intechopen.69282 153

**Figure 13.** The CBCT imaging of a patient with right mandibular condylar hyperplasia (red arrows).

152 Computed Tomography - Advanced Applications

**Figure 14.** The 3D CBCT imaging of a patient with mandibular asymmetry who needs orthognathic surgery.

**Figure 15.** The multi-planar CBCT imaging of a patient with cleft palate on the left site. **a.** Before cleft repair surgery. **b.** After bone augmentation surgery.

**Figure 16.** The 3D CBCT imaging of a patient with bilateral elongated styloid process (Eagle syndrome). Note that the length and medial angulations of the styloid process can be measured by using CBCT software.

#### **3.2. Orthodontics**

Radiographic analysis is an important aspect for diagnosis and treatment planning in orthodontics. CBCT imaging allows the radiographic assessments in detail with lower radiation doses and without any distortion and superimposition of the other structures. The airway analysis before and after orthognathic surgeries, growth assessment, accurate measurements of cleft area in cleft lip and palate patients, assessment of skeletal and dental structures, assessment of TMJ complex, treatment planning for orthognathic surgery, accurate estimation of space requirement for unerupted or impacted teeth, assessment of orthodontics-induced root resorption, determination of possible regions for mini screw placement, and linear and angular measurements for severe skeletal discrepancies can be performed with CBCT imaging.

The CBCT imaging can be used to assess the amount of interradicular bone, root proximity, the localization of maxillary sinus and inferior alveolar nerve, and density of the available bone, all of which are important in determining the stability and success of orthodontic mini screws. Due to the considerable variation of available bone thickness between individuals, a CBCT imaging is recommended in order to determine the maximum screw length [38]. A CBCT imaging study indicated that vertical facial pattern of the patients should be taken into consideration when adjusting the insertion angle of mini screws at the maxillary buccal site [39].

CBCT can also be used in association with CAD/CAM technology for production of custommade orthodontic appliances [40].

In terms of evaluation of impacted teeth, small volume of CBCT can be used as a supplement to panoramic imaging in the following cases: when canine inclination in the panoramic X-ray exceeds 30°, when root resorption is suspected at adjacent teeth, and when the canine apex is not clearly seen in the panoramic X-ray [41].

The CBCT scans can be used to evaluate the outcomes of orthodontic treatments and orthognathic surgery. The 3D overlays of superimposed models and 3D color-coded displacement maps provided assessments of treatment changes, displacements of soft and hard tissue during postsurgical follow-up, and amount of relapse [42, 43].

The landmark identification is greatly enhanced in CBCT images. It was reported that reproducibility of cephalometric measurements obtained from CBCT scans was better than that obtained from conventional cephalograms [44]. One of the application areas of CBCT for orthodontics is the growth assessment of patients. The cervical vertebra maturity assessment with CBCT provides reliable assessment of pubertal growth; thus, CBCT can be used to evaluate skeletal maturity for orthodontic treatment [45]. For airway analysis, lateral cephalograms have been routinely used. Axial cuts of 3D CBCT scans provide soft tissue points which are more clearly visible in CBCT sections compared with conventional radiography, thereby enhancing airway assessment [46]. The CBCT-assisted airway analysis also facilitates the diagnosis and treatment planning of obstructive sleep apnea (OSA) [47]. A recent CBCT imaging study concluded that 3D image reconstruction accurately confirmed morphological changes in the upper airway during oral appliance therapy of patients with OSA [48]. In terms of airway analysis with CBCT technology, there are controversial conclusions in literature. A recent systematic review shows that upper pharyngeal airway analysis using CBCT is a reliable method; however, there are some significant limitations including lack of manual orientation of images and selection of threshold sensitivity. Thus, further researches are necessary to adequately establish the reliability of airway analysis with CBCT imaging [49]. A CBCT image used for airway analysis is shown in **Figure 17**.

### **3.3. Periodontology**

**3.2. Orthodontics**

154 Computed Tomography - Advanced Applications

Radiographic analysis is an important aspect for diagnosis and treatment planning in orthodontics. CBCT imaging allows the radiographic assessments in detail with lower radiation doses and without any distortion and superimposition of the other structures. The airway analysis before and after orthognathic surgeries, growth assessment, accurate measurements of cleft area in cleft lip and palate patients, assessment of skeletal and dental structures, assessment of TMJ complex, treatment planning for orthognathic surgery, accurate estimation of space requirement for unerupted or impacted teeth, assessment of orthodontics-induced root resorption, determination of possible regions for mini screw placement, and linear and angular measurements for severe skeletal discrepancies can be performed with CBCT imaging.

**Figure 16.** The 3D CBCT imaging of a patient with bilateral elongated styloid process (Eagle syndrome). Note that the

length and medial angulations of the styloid process can be measured by using CBCT software.

The CBCT imaging can be used to assess the amount of interradicular bone, root proximity, the localization of maxillary sinus and inferior alveolar nerve, and density of the available bone, all of which are important in determining the stability and success of orthodontic mini screws. Due to the considerable variation of available bone thickness between individuals, a CBCT imaging is recommended in order to determine the maximum screw length [38]. A CBCT The role of CBCT in the diagnosis of periodontal diseases was studied in literature. CBCT displays 2D and 3D images that are necessary for the diagnosis and treatment planning of intrabony defects, furcation involvements, and buccal/lingual bone destructions [50]. In a recent experimental animal study, the diagnostic value of CBCT and digital intraoral radiography for detection of periodontal defects including furcation involvements, one-, two-, three-wall and trough-like intrabony defects, fenestration, and dehiscence were compared. It was concluded that CBCT was superior to digital radiography for detection of grade 1 furcation involvements, three-wall defects, fenestrations, and dehiscences [51]. It is also clinically reported that CBCT imaging provides detailed information about furcation involvement and reliable basis for decision of periodontal treatment [52]. In literature, most of the studies

**Figure 17.** The right lateral view of pharyngeal airway on CBCT image (A: anterior nasal plane, B: posterior nasal plane, C: upper pharyngeal plane, D: middle pharyngeal plane, E: lower pharyngeal plane, FHD: Frankfurt horizontal plane).

concerning the accuracy of CBCT in periodontal diagnosis assessed the efficiency of CBCT in bone defects. However, in our recent study, we concluded that gingival soft tissue thickness and acellular dermal grafts can be consistently evaluated with CBCT technique [53]. The detailed diagnostic imaging of periodontal diseases as well as peri-implantitis may be performed with CBCT technology (**Figures 18** and **19**). Literature shows that optimal detection of peri-implant bone loss is achieved using the smallest FOV, the highest number of acquisition frames, and the smallest voxel [54]. When the CBCT-derived features of peri-implantitis defects compared to the corresponding histomorphometric findings, it is concluded that CBCT represents an accurate diagnostic tool to estimate the histological extent of peri-implantitis [55]. When the performances of different radiographic techniques (intraoral radiography, OPG, CBCT, and CT) in detecting peri-implant bone defects were compared, the highest sensitivity was found with intraoral radiography and CBCT, and the highest specificity was found with intraoral radiography, while CT demonstrated the lowest performance [56].

### **3.4. Endodontics**

The CBCT imaging for endodontic purposes provides the clinicians' wide view in the visualization of periapical lesions, internal or external root resorption, vertical root fractures, and accessory root canals. It was found that CBCT assessment of changes in periapical lesion and mucosal thickening dimensions may reveal useful information regarding endodontic treatment success [57]. The CBCT imaging also guides the clinicians for planning endodontic surgery and in elucidation of causes of fail after endodontic treatment [10, 58]. However, there are two major disadvantages concerning the utilization of CBCT in endodontics: The increased radiation doses, compared to 2D imaging methods, limit its routine usage. Thus, benefits Cone-Beam Computed Tomography for Oral and Maxillofacial Imaging http://dx.doi.org/10.5772/intechopen.69282 157

**Figure 18.** The CBCT imaging of a periodontitis case. Note that the amount of bone resorption around mandibular incisor tooth can be measured in detail using CBCT software.

concerning the accuracy of CBCT in periodontal diagnosis assessed the efficiency of CBCT in bone defects. However, in our recent study, we concluded that gingival soft tissue thickness and acellular dermal grafts can be consistently evaluated with CBCT technique [53]. The detailed diagnostic imaging of periodontal diseases as well as peri-implantitis may be performed with CBCT technology (**Figures 18** and **19**). Literature shows that optimal detection of peri-implant bone loss is achieved using the smallest FOV, the highest number of acquisition frames, and the smallest voxel [54]. When the CBCT-derived features of peri-implantitis defects compared to the corresponding histomorphometric findings, it is concluded that CBCT represents an accurate diagnostic tool to estimate the histological extent of peri-implantitis [55]. When the performances of different radiographic techniques (intraoral radiography, OPG, CBCT, and CT) in detecting peri-implant bone defects were compared, the highest sensitivity was found with intraoral radiography and CBCT, and the highest specificity was found with intraoral

**Figure 17.** The right lateral view of pharyngeal airway on CBCT image (A: anterior nasal plane, B: posterior nasal plane, C: upper pharyngeal plane, D: middle pharyngeal plane, E: lower pharyngeal plane, FHD: Frankfurt horizontal plane).

The CBCT imaging for endodontic purposes provides the clinicians' wide view in the visualization of periapical lesions, internal or external root resorption, vertical root fractures, and accessory root canals. It was found that CBCT assessment of changes in periapical lesion and mucosal thickening dimensions may reveal useful information regarding endodontic treatment success [57]. The CBCT imaging also guides the clinicians for planning endodontic surgery and in elucidation of causes of fail after endodontic treatment [10, 58]. However, there are two major disadvantages concerning the utilization of CBCT in endodontics: The increased radiation doses, compared to 2D imaging methods, limit its routine usage. Thus, benefits

radiography, while CT demonstrated the lowest performance [56].

**3.4. Endodontics**

156 Computed Tomography - Advanced Applications

**Figure 19.** The CBCT imaging of a peri-implantitis case showing bone resorption around dental implant.

getting with CBCT imaging should be carefully evaluated on an individual basis to protect the patients. The other disadvantage is that the radiopaque filling materials and posts crate artifacts which may compromise the diagnosis.

In a recent clinical study, it was reported that CBCT scans had 93% sensitivity, 78% specificity, and 88% accuracy for detection of vertical root fractures in endodontically treated teeth [59]. When CBCT and digital periapical radiography were compared in detecting mandibular molar root perforations, in the non-obturated root canals, the sensitivity and specificity of CBCT scans in perforation detection were better than those of three-angled periapical radiographs. However, in obturated root canals, periapical radiography was reported to be more trustworthy than CBCT for perforation detection [60]. In a recent study, periapical radiographs and CBCT were compared in detecting fractured instruments in root canals with and without filling. The results showed that in the absence of filling, accuracy values were similar in all imaging techniques. In the presence of filling, CBCT had low accuracy [61]. In our recent clinical study, we observed that preoperative CBCT examination demonstrated positive contributions to the endodontic surgery of maxillary first molar teeth [62]. Maxillary posterior teeth have close relationship with maxillary sinus. This may cause the peri-radicular infection to destroy cortical border of the maxillary sinus and spread into the sinus. Such cases may make the clinician to do false or missing diagnosis. In such cases, CBCT imaging allows the practitioner to do appropriate diagnosis of the peri-radicular lesion and its relationship with the adjacent anatomic structures [63]. A CBCT image acquired for planning of endodontic surgery is shown in **Figure 20**.

**Figure 20.** The example of CBCT imaging acquired for detailed assessment of mandibular first molar tooth after endodontic treatment.

In conclusion, according to the contemporary literature, the decision to perform a CBCT examination in endodontics should be kept in limited due to its low accuracy in diagnosis. However, utilization of CBCT may give more benefits in planning endodontic surgery.

### **3.5. Otolaryngology**

getting with CBCT imaging should be carefully evaluated on an individual basis to protect the patients. The other disadvantage is that the radiopaque filling materials and posts crate

In a recent clinical study, it was reported that CBCT scans had 93% sensitivity, 78% specificity, and 88% accuracy for detection of vertical root fractures in endodontically treated teeth [59]. When CBCT and digital periapical radiography were compared in detecting mandibular molar root perforations, in the non-obturated root canals, the sensitivity and specificity of CBCT scans in perforation detection were better than those of three-angled periapical radiographs. However, in obturated root canals, periapical radiography was reported to be more trustworthy than CBCT for perforation detection [60]. In a recent study, periapical radiographs and CBCT were compared in detecting fractured instruments in root canals with and without filling. The results showed that in the absence of filling, accuracy values were similar in all imaging techniques. In the presence of filling, CBCT had low accuracy [61]. In our recent clinical study, we observed that preoperative CBCT examination demonstrated positive contributions to the endodontic surgery of maxillary first molar teeth [62]. Maxillary posterior teeth have close relationship with maxillary sinus. This may cause the peri-radicular infection to destroy cortical border of the maxillary sinus and spread into the sinus. Such cases may make the clinician to do false or missing diagnosis. In such cases, CBCT imaging allows the practitioner to do appropriate diagnosis of the peri-radicular lesion and its relationship with the adjacent anatomic structures [63]. A CBCT image acquired for planning of endodontic surgery is shown in **Figure 20**.

**Figure 20.** The example of CBCT imaging acquired for detailed assessment of mandibular first molar tooth after

endodontic treatment.

artifacts which may compromise the diagnosis.

158 Computed Tomography - Advanced Applications

Depending on the FOV used, CBCT images may show partial or the entire nasal cavity, paranasal sinuses, airway, cervical vertebrae, and temporal bone. In fact, specific ear, nose, and throat imaging programs have been increasingly included in CBCT systems, suggesting that CBCT may at some point entirely replace medical CT imaging in certain otolaryngologyrelated applications [64]. In terms of otolaryngology, CBCT imaging can be used to assess airway, paranasal sinus pathologies, nasal polyps, temporal and frontal bone anatomy, middle ear, and cochlear implantation [9, 65–68]. As an imaging guidance, CBCT can be used to treat lymphatic leakage after thyroidectomy [69]. The CBCT-based percutaneous image-guided technique may provide mini invasivity and identification of the anatomy and site of the leakage. An example of CBCT imaging used for detailed assessment of maxillary sinus volume is shown in **Figure 21**.

#### **3.6. Forensic medicine**

One of the contemporary application fields of CBCT for maxillofacial imaging is forensic medicine. Age estimation of individuals is an important aspect of forensic science. The CBCT can also be used as new method of age estimation by measuring the pulp-to-tooth area ratio

**Figure 21.** An example of CBCT imaging showing measurement of maxillary sinus volume.

in 3D images in living individuals [70, 71]. The forensic age estimation can also be performed using CBCT-derived analysis of spheno-occipital synchondrosis [72].

Moreover, the CBCT-derived anthropometric measurements on mandibular images can be used for sex estimation in forensic settings [73]. Besides age and sex estimation, CBCT can be used in forensic science for identification of unknown human bodies through frontal sinus 3D superimposition technique [74].

### **4. Conclusion**

In the present chapter, a review of literature related to the clinical applications of CBCT technique for oral and maxillofacial imaging was undertaken with illustrated sample cases. Tremendous advancements have been acquired after the introduction of CBCT imaging technology especially for oral and maxillofacial practice. The contributions of CBCT for maxillofacial imaging have been demonstrated in several studies for diagnosis, treatment planning, evaluation of treatment outcome, and research purposes. The widespread use of CBCT in maxillofacial region represents the most important advance in diagnostic radiology without disadvantages of multi-slice CT especially including high radiation dose and increased cost. In most of the cases in OMF region, CBCT takes the place of multi-slice CT. Dentists and clinicians dealing with this field should have the knowledge of working principles, requirements, appropriate indications, clinical benefits, drawbacks, and hazardous effects of CBCT technology for proper utilization. In literature, there were inconsistencies and discrepancies about the CBCT device settings, properties, radiation doses, image acquisition protocol, and estimation of bone density which confuse the readers. The most common clinical applications of CBCT were in OMF surgery including implantology and impacted teeth. The subjective image quality was higher in multi-slice CT than in older CBCT units. However, the recent CBCT units showed opposite results. Moreover, new CBCT units with flat panel detectors seem to be less prone to metal artifacts. The CBCT provides less radiation than multi-slice CT but more than panoramic X-ray. Thus, it is crucial that the ALARA principle ("As Low As Reasonably Achievable" radiation dose) should be respected.

### **Author details**

Ufuk Tatli<sup>1</sup> \* and Burcu Evlice<sup>2</sup>

\*Address all correspondence to: dr.ufuktatli@gmail.com

1 Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Çukurova University, Adana, Turkey

2 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Çukurova University, Adana, Turkey

### **References**

in 3D images in living individuals [70, 71]. The forensic age estimation can also be performed

Moreover, the CBCT-derived anthropometric measurements on mandibular images can be used for sex estimation in forensic settings [73]. Besides age and sex estimation, CBCT can be used in forensic science for identification of unknown human bodies through frontal sinus 3D

In the present chapter, a review of literature related to the clinical applications of CBCT technique for oral and maxillofacial imaging was undertaken with illustrated sample cases. Tremendous advancements have been acquired after the introduction of CBCT imaging technology especially for oral and maxillofacial practice. The contributions of CBCT for maxillofacial imaging have been demonstrated in several studies for diagnosis, treatment planning, evaluation of treatment outcome, and research purposes. The widespread use of CBCT in maxillofacial region represents the most important advance in diagnostic radiology without disadvantages of multi-slice CT especially including high radiation dose and increased cost. In most of the cases in OMF region, CBCT takes the place of multi-slice CT. Dentists and clinicians dealing with this field should have the knowledge of working principles, requirements, appropriate indications, clinical benefits, drawbacks, and hazardous effects of CBCT technology for proper utilization. In literature, there were inconsistencies and discrepancies about the CBCT device settings, properties, radiation doses, image acquisition protocol, and estimation of bone density which confuse the readers. The most common clinical applications of CBCT were in OMF surgery including implantology and impacted teeth. The subjective image quality was higher in multi-slice CT than in older CBCT units. However, the recent CBCT units showed opposite results. Moreover, new CBCT units with flat panel detectors seem to be less prone to metal artifacts. The CBCT provides less radiation than multi-slice CT but more than panoramic X-ray. Thus, it is crucial that the ALARA principle ("As Low As Reasonably Achievable" radiation dose) should be

1 Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Çukurova University,

2 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Çukurova University,

using CBCT-derived analysis of spheno-occipital synchondrosis [72].

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160 Computed Tomography - Advanced Applications

**4. Conclusion**

respected.

Ufuk Tatli<sup>1</sup>

Adana, Turkey

Adana, Turkey

**Author details**

\* and Burcu Evlice<sup>2</sup>

\*Address all correspondence to: dr.ufuktatli@gmail.com


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[60] Haghanifar S, Moudi E, Mesgarani A, Bijani A, Abbaszadeh N. A comparative study of cone-beam computed tomography and digital periapical radiography in detecting mandibular molars root perforations. Imaging Science in Dentistry. 2014;**44**:115-119.

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166 Computed Tomography - Advanced Applications

s00405-016-4345-2


**Usefulness of Cone Beam Computed Tomography for the Diagnosis and Treatment of Oral and Maxillofacial Pathology**

Márcio Diniz-Freitas, Javier Fernández-Feijoo,

Lucía García-Caballero, Maite Abeleira,

Mercedes Outumuro, Jacobo Limeres-Pose and

Pedro Diz-Dios

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68313

### **Abstract**

Three-dimensional (3D) evaluation of oral and maxillofacial pathology, in comparison with two-dimensional (2D) radiological studies, offers many advantages that can assist in the diagnostic and in the preoperative evaluation of certain lesions and conditions of the jaws, reducing the risk of intraoperative and postoperative complications. The introduction of cone beam computed tomography (CBCT) represents an important technological advance in the context of oral and maxillofacial radiology as it permits the acquisition of high-quality 3D images and dynamic navigation over an area of interest in real time, with a short scan time and lower dose of radiation than conventional computed tomography (CT). The initial indications for CBCT have been extended by the progressive addition of new ones such as evaluation of the extent of osteonecrotic lesions of the jaw due to bisphosphonates, preoperative staging of oral cancer, and planning reconstructive surgery. As a consequence, this radiological technique represents an interesting complement to conventional radiology in those clinical situations in which 3D imaging can facilitate diagnosis and/or treatment.

**Keywords:** cone beam computed tomography, oral maxillofacial radiology, oral maxillofacial pathology

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **1. Introduction**

Radiological evaluation of the size of a lesion, its density, thickness of the adjacent bone, and distance from anatomically nearby structures can assist in the diagnostic and in the preoperative evaluation of certain lesions and conditions of the jaws, reduce the risk of intraoperative and postoperative complications, and reduce surgical stress on the surgeon [1]. However, although two-dimensional (2D) radiological studies provide relevant information, in many situations they have limitations, such as indicating the location and size of a lesion in the buccolingual plane, showing characteristics of the surface (smooth or rough), and demonstrating changes that develop over time in order to evaluate progression of the lesion. As a consequence, three-dimensional (3D) studies are valuable in order to improve the diagnosis and treatment of these lesions.

Cone beam computed tomography (CBCT), also known as digital volumetric tomography (DVT) [2], volumetric computed tomography (VCT), or cone beam three-dimensional imaging (CB3D) [3], is a relatively new technology in the field of oral and maxillofacial radiology, but it is rapidly becoming established as the radiological technique of choice in numerous clinical situations [4]. CBCT enables a large quantity of data to be acquired with a short scan time and low dose of radiation compared with conventional computed tomography (CT). CBCT uses a conical X-ray beam (in contrast to the fan beam of conventional CT) and a special detector that, depending on the technology developed by the manufacturers, may be an image intensifier tube or an amorphous silicon flat-panel detector [4]. The X-ray source and reciprocal detector rotate synchronously around the head of the patient, in a single scan. Single projection images, known as "basis" images, are acquired at predetermined degree intervals. Software programs incorporating back-filtered projection are applied to the series of base images to generate a 3D volumetric data set, creating a spherical or a cylindrical volume called the "field of view" (FOV), which can be used to provide primary reconstruction images in three orthogonal planes (axial, sagittal, and coronal) [5].

The objective of this chapter is to provide a brief review of this new technology, its advantages and disadvantages, and its possible applications in the area of oral and maxillofacial pathology.

### **2. Clinical applications in dentistry**

One of the main indications for CBCT is to determine bone availability for implant surgery [6]. However, the usefulness of CBCT imaging of the oral and maxillofacial region is continually increasing. Particularly useful indications include the diagnosis of bone disease (including maxillofacial fractures and deformities), preoperative evaluation of dental impaction, study of the temporomandibular joint, 3D cephalometric analysis in orthodontic practice, and diagnosis and surgical simulation in orthognathic surgery and in patients with cleft palate [7].

There now follows a summary of the most important studies on the use of CBCT in oral and maxillofacial pathology.

### **2.1. Disorders of tooth eruption**

An important clinical application of CBCT is the diagnosis and planning of treatment for tooth eruption alterations. In this field, CBCT provides multiplanar visualization of the position of the tooth and its relationship with neighboring anatomical structures, as well as the presence of associated conditions, such as cystic degeneration of the dental follicle and root reabsorption of adjacent teeth, all of which are important factors in the therapeutic decision-taking process.

### *2.1.1. Dental inclusions*

**1. Introduction**

170 Computed Tomography - Advanced Applications

and treatment of these lesions.

in three orthogonal planes (axial, sagittal, and coronal) [5].

**2. Clinical applications in dentistry**

maxillofacial pathology.

Radiological evaluation of the size of a lesion, its density, thickness of the adjacent bone, and distance from anatomically nearby structures can assist in the diagnostic and in the preoperative evaluation of certain lesions and conditions of the jaws, reduce the risk of intraoperative and postoperative complications, and reduce surgical stress on the surgeon [1]. However, although two-dimensional (2D) radiological studies provide relevant information, in many situations they have limitations, such as indicating the location and size of a lesion in the buccolingual plane, showing characteristics of the surface (smooth or rough), and demonstrating changes that develop over time in order to evaluate progression of the lesion. As a consequence, three-dimensional (3D) studies are valuable in order to improve the diagnosis

Cone beam computed tomography (CBCT), also known as digital volumetric tomography (DVT) [2], volumetric computed tomography (VCT), or cone beam three-dimensional imaging (CB3D) [3], is a relatively new technology in the field of oral and maxillofacial radiology, but it is rapidly becoming established as the radiological technique of choice in numerous clinical situations [4]. CBCT enables a large quantity of data to be acquired with a short scan time and low dose of radiation compared with conventional computed tomography (CT). CBCT uses a conical X-ray beam (in contrast to the fan beam of conventional CT) and a special detector that, depending on the technology developed by the manufacturers, may be an image intensifier tube or an amorphous silicon flat-panel detector [4]. The X-ray source and reciprocal detector rotate synchronously around the head of the patient, in a single scan. Single projection images, known as "basis" images, are acquired at predetermined degree intervals. Software programs incorporating back-filtered projection are applied to the series of base images to generate a 3D volumetric data set, creating a spherical or a cylindrical volume called the "field of view" (FOV), which can be used to provide primary reconstruction images

The objective of this chapter is to provide a brief review of this new technology, its advantages and disadvantages, and its possible applications in the area of oral and maxillofacial pathology.

One of the main indications for CBCT is to determine bone availability for implant surgery [6]. However, the usefulness of CBCT imaging of the oral and maxillofacial region is continually increasing. Particularly useful indications include the diagnosis of bone disease (including maxillofacial fractures and deformities), preoperative evaluation of dental impaction, study of the temporomandibular joint, 3D cephalometric analysis in orthodontic practice, and diagnosis and surgical simulation in orthognathic surgery and in patients with cleft palate [7]. There now follows a summary of the most important studies on the use of CBCT in oral and The extraction of impacted third molars is a common procedure in dental practice. In the majority of cases, it is a simple procedure with a minimal risk of damage to adjacent structures; however, in some cases, there is an intimate relationship between the roots of the mandibular third molars and the mandibular canal or the lingual cortical plate of the mandible, making it important to evaluate the topographical relationship between the third molar and these structures (**Figure 1**). Other characteristics that must be evaluated preoperatively are

**Figure 1.** Inferior left third molar inclusion. (a) Detail of the panoramic reconstruction on CBCT in which the close relationship with the inferior alveolar nerve (IAN) canal (continuos line) is observed. (b) Cross-sectional images showing the three-dimensional location of the unerupted tooth and its relationship with the IAN (dark point). (c) Preoperative planning of surgical exodontia based on three-dimensional reconstruction (CS3D Imaging, CareStream, Rochester, NY).

angulation with respect to the sagittal plane, buccolingual inclination, size and shape of the crown, and the presence of local lesions. With respect to the roots of the tooth, the most important characteristic is their relationship with the mandibular canal, though it is also important to determine factors such as the number and shape of the roots and their stage of development in order to predict surgical difficulty [8, 9]. Oral and maxillofacial surgeons tend to use panoramic radiographs for evaluation of the morphology of impacted third molars and their relationship with the mandibular canal [10]. A number of radiological criteria suggestive of an intimate relationship between these two structures have been described in the literature. Sedaghatfar et al. [11] found that darkening of the root, interruption of the radiopaque lines that represent the roof and floor of the mandibular canal, divergence of the mandibular canal, and narrowing of the root on the panoramic radiograph were significantly associated with exposure of the inferior alveolar nerve after extraction of the mandibular third molars. Tantanapornkul et al. [12] found that these four criteria used independently were able to predict exposure of the nerve packet after third molars extraction, but in the multivariate analysis only interruption of the wall of the canal predicted nerve exposure. When the findings on the panoramic radiograph suggest an intimate relationship between the impacted tooth and the mandibular canal, some authors recommend complementary studies with CT or CBCT [13]. Using CBCT, Tantanapornkul et al. [12] found a sensitivity of 93% and a specificity of 77% for the prediction of inferior alveolar nerve exposure after third molar extraction, improving on the results obtained with panoramic radiographs. Exposure of the nerve correlated significantly with the presence of altered sensitivity in the postoperative follow-up. Recent studies based on images obtained by CBCT have shown that darkening of the root observed on the panoramic radiograph is more closely related with a reduction in the thickness or perforation of the lingual cortical plate than with the presence of an intimate relationship between the third molar and the mandibular canal. Thinning or perforation of the lingual cortical plate was confirmed on CBCT in 80% of cases in which darkening of the root was observed on panoramic radiograph [14]. When compared to a combination of 2D radiographs (panoramic radiography and cephalometric radiography), CBCT showed a higher detection quality of the relationship between the mandibular canal and the root tips of the third molars [15]. In addition, it has also been shown that CBCT is able to identify accessory roots and apical anomalies/curvatures not visible in the panoramic radiography [16].

Although two-dimensional imaging (panoramic and periapical radiography) is sufficient in most cases prior to the extraction of the lower third molars, CBCT may be indicated in cases where the two-dimensional image suggests one or more signs of close contact relationship between the third molar and the IDN, and if it is believed that the CBCT will change the treatment plan or the patient's prognosis [17].

With respect to the maxillary third molars, CBCT can be used to evaluate the relationship between the roots and the floor of the maxillary sinus [18] (**Figure 2**). Another advantage of CBCT in the preoperative evaluation of third molar surgery is the possibility of significantly decreasing the surgeon's level of stress in complex cases and reducing the duration of surgery.

The second most common dental impaction after the third molars is the maxillary canine, with a prevalence that varies between 1 and 2.5% [19]. Due to their functional and esthetic Usefulness of Cone Beam Computed Tomography for the Diagnosis and Treatment of Oral... http://dx.doi.org/10.5772/intechopen.68313 173

angulation with respect to the sagittal plane, buccolingual inclination, size and shape of the crown, and the presence of local lesions. With respect to the roots of the tooth, the most important characteristic is their relationship with the mandibular canal, though it is also important to determine factors such as the number and shape of the roots and their stage of development in order to predict surgical difficulty [8, 9]. Oral and maxillofacial surgeons tend to use panoramic radiographs for evaluation of the morphology of impacted third molars and their relationship with the mandibular canal [10]. A number of radiological criteria suggestive of an intimate relationship between these two structures have been described in the literature. Sedaghatfar et al. [11] found that darkening of the root, interruption of the radiopaque lines that represent the roof and floor of the mandibular canal, divergence of the mandibular canal, and narrowing of the root on the panoramic radiograph were significantly associated with exposure of the inferior alveolar nerve after extraction of the mandibular third molars. Tantanapornkul et al. [12] found that these four criteria used independently were able to predict exposure of the nerve packet after third molars extraction, but in the multivariate analysis only interruption of the wall of the canal predicted nerve exposure. When the findings on the panoramic radiograph suggest an intimate relationship between the impacted tooth and the mandibular canal, some authors recommend complementary studies with CT or CBCT [13]. Using CBCT, Tantanapornkul et al. [12] found a sensitivity of 93% and a specificity of 77% for the prediction of inferior alveolar nerve exposure after third molar extraction, improving on the results obtained with panoramic radiographs. Exposure of the nerve correlated significantly with the presence of altered sensitivity in the postoperative follow-up. Recent studies based on images obtained by CBCT have shown that darkening of the root observed on the panoramic radiograph is more closely related with a reduction in the thickness or perforation of the lingual cortical plate than with the presence of an intimate relationship between the third molar and the mandibular canal. Thinning or perforation of the lingual cortical plate was confirmed on CBCT in 80% of cases in which darkening of the root was observed on panoramic radiograph [14]. When compared to a combination of 2D radiographs (panoramic radiography and cephalometric radiography), CBCT showed a higher detection quality of the relationship between the mandibular canal and the root tips of the third molars [15]. In addition, it has also been shown that CBCT is able to identify accessory roots and apical anoma-

lies/curvatures not visible in the panoramic radiography [16].

ment plan or the patient's prognosis [17].

172 Computed Tomography - Advanced Applications

Although two-dimensional imaging (panoramic and periapical radiography) is sufficient in most cases prior to the extraction of the lower third molars, CBCT may be indicated in cases where the two-dimensional image suggests one or more signs of close contact relationship between the third molar and the IDN, and if it is believed that the CBCT will change the treat-

With respect to the maxillary third molars, CBCT can be used to evaluate the relationship between the roots and the floor of the maxillary sinus [18] (**Figure 2**). Another advantage of CBCT in the preoperative evaluation of third molar surgery is the possibility of significantly decreasing the surgeon's level of stress in complex cases and reducing the duration of surgery.

The second most common dental impaction after the third molars is the maxillary canine, with a prevalence that varies between 1 and 2.5% [19]. Due to their functional and esthetic

**Figure 2.** Third upper left molar inclusion. (a) View of the panoramic reconstruction and the cross-sectional images where an intimate relationship is observed with the roots of the second molar. (b) Preoperative planning of surgical exodontia based on three-dimensional reconstruction (I-CAT Vision, Imaging Sciences International, Hatfield, PA, USA).

relevance, the main objective in the treatment of impacted canines is their repositioning in the dental arch. Their 3D localization (**Figure 3**) is therefore important both for diagnosis and for the surgical-orthodontic management; this localization can be particularly difficult to explore with conventional radiological methods due to overlying anatomical structures [20]. CBCT can provide additional data not available with conventional 2D studies, such as the size of the follicle, the degree of inclination of the long axis of the tooth, facial-palatal position, the quantity of bone covering the tooth, the proximity and reabsorption of adjacent roots, and the stage of development of the tooth [21]. There are reports of the use of CBCT in the management of both maxillary- and mandibular-impacted canines [22]. Liu et al. [23] used CBCT to study the position and angulation of 210 impacted maxillar canines, the presence of reabsorption of the adjacent incisors, and the thickness of the dental follicle. These authors recommended complementary radiographic study using CBCT in those patients with impacted canines with marked displacement, possible reabsorption of adjacent incisors, or cystic degeneration of the dental follicle. Recently, How Kau et al. [24] proposed a new classification system—the KPG

**Figure 3.** Left maxillary impacted canine. (a) Panoramic radiography; (b) cone beam computed tomography (CBCT) reconstruction obtained with I-CAT system (Imaging Sciences International, Hatfield, PA, USA); (c) cross-sectional images obtained with I-CAT system showing the three-dimensional location of the unerupted tooth and its relationship with adjacent anatomic structures.

index—based on the tridimensional localization of impacted canines provided by CBCT to predict the difficulty of treatment. However, this new classification system needs to be validated by prospective longitudinal studies. A recent systematic review concluded that CBCT is more accurate than conventional radiographs in localizing maxillary-impacted canine [25].

#### *2.1.2. Supernumerary teeth*

Supernumerary teeth are usually asymptomatic and are identified during routine radiological evaluation. Radiological study is useful to determine their position. Traditionally, such studies have used periapical, occlusal, and lateral skull radiographs. Periapical radiographs provide a detailed view of the anatomy of the tooth and, through the Clark's rule [26], can be used to establish the buccolingual and the palatal position of the tooth. However, these radiographs frequently do not enable a 3D evaluation to be made of the supernumerary tooth with respect to adjacent teeth and neighboring anatomical structures (**Figure 4**); this information can be important to determine the treatment plan. Liu et al. [27] used CBCT to study 487 patients with a total of 626 supernumerary teeth; in addition, panoramic and lateral skull radiographs had been performed previously in 50 of these patients with supernumerary teeth in the anterior region, allowing comparison of the visualization of the teeth and the adjacent bone structures with the three techniques. CBCT provided visualization qualified as "excellent" in practically all cases (there were only six cases in which visualization of the apices of the incisors was qualified as "reasonable"). CBCT was superior to the panoramic and lateral skull radiographs for all radiological criteria evaluated. Based on these results, the authors recommended that the evaluation of supernumerary teeth should routinely be performed by CBCT, particularly in those cases with multiple supernumerary teeth, malocclusions, or a high intramaxillary position. When extraction of supernumerary teeth is indicated, 3D localization by CBCT can help the surgeon in the choice of surgical access and identification of the tooth to be extracted, reducing trauma to the adjacent soft and hard tissues (**Figure 5**).

index—based on the tridimensional localization of impacted canines provided by CBCT to predict the difficulty of treatment. However, this new classification system needs to be validated by prospective longitudinal studies. A recent systematic review concluded that CBCT is more accurate than conventional radiographs in localizing maxillary-impacted canine [25].

**Figure 3.** Left maxillary impacted canine. (a) Panoramic radiography; (b) cone beam computed tomography (CBCT) reconstruction obtained with I-CAT system (Imaging Sciences International, Hatfield, PA, USA); (c) cross-sectional images obtained with I-CAT system showing the three-dimensional location of the unerupted tooth and its relationship

Supernumerary teeth are usually asymptomatic and are identified during routine radiological evaluation. Radiological study is useful to determine their position. Traditionally, such studies have used periapical, occlusal, and lateral skull radiographs. Periapical radiographs provide a detailed view of the anatomy of the tooth and, through the Clark's rule [26], can be used to establish the buccolingual and the palatal position of the tooth. However, these

*2.1.2. Supernumerary teeth*

with adjacent anatomic structures.

174 Computed Tomography - Advanced Applications

**Figure 4.** Supernumerary teeth in the posterior zone of the right inferior jaw. (a–c) Buccolingual localization and relationship with the mental foramen based on the multiplanar (MPR) reconstruction and cross-sectional images (I-Cat Vision). (d, e) Surgical removal of the supernumerary tooth.

**Figure 5.** Supernumerary teeth in the anterior portion of the upper jaw. (a) Cone beam computed tomography (CBCT) reconstruction obtained with I-CAT system (Imaging Sciences International, Hatfield, PA, USA); (b) cross-sectional view of the supernumerary teeth and their relationship with adjacent anatomic structures. Notice a crown erupting in the nasal floor (arrows).

#### **2.2. Periapical disease**

Conventional radiographic techniques provide limited information about the origin, size, and situation of periapical lesions [28]. Superposition of adjacent anatomical and dental structures makes it necessary to perform a number of images from different angles [29]. It should be noted that the effective dose of radiation of two periapical radiographs in the area of the molars is of between 0.01 and 0.02 μSv [30], whereas the dose with limited CBCT is between 0.006 and 0.012 μSv [31].

Experimental studies have shown that CBCT is superior to digital or conventional intraoral radiography for the detection of chemically [32] or mechanically [33] induced periapical lesions. Lofthag-Hansen et al. [29] demonstrated the utility of limited CBCT for the detection of periapical pathosis not identified by conventional intraoral radiography. With CBCT, these authors found a larger number of teeth and roots involved and a larger number of lesions extending toward the maxillary sinus than on periapical radiographs. In 70% of the cases studied, the examiners considered that CBCT provided relevant additional diagnostic information in comparison with intraoral radiographs. The authors recommend the use of CBCT when there is a clinical suspicion of periapical disease and no pathology is detected on conventional radiographic techniques, as well as to plan periapical surgery for multi-rooted teeth. On the same subject, Estrela et al. [34] demonstrated that panoramic and periapical radiographs underestimated both the number and size of periapical lesions in comparison with CBCT. Estrela et al. [35] compared CBCT and intraoral radiographs for the diagnosis of periapical pathology in 596 patients with one or more endodontically treated teeth. Periapical pathology was detected in 60.9% of cases with CBCT and in 39.5% with intraoral radiographs. Based on these results, the authors proposed a new classification—the periapical index—for periapical pathosis based on the diameter of the lesion and on the expansion or destruction of cortical bone.

CBCT can also be used as a noninvasive diagnostic technique in periapical pathosis. Simon et al. [36] compared the diagnosis of large periapical lesions (granulomas vs. cysts) using CBCT and biopsy. These authors examined 17 lesions with a size equal to or greater than 1 cm × 1 cm, making a preoperative diagnosis based on the density of the lesions measured by CBCT. There was concordance between the preoperative diagnosis based on CBCT and the histological study in 13 of 17 cases. In four of the 17 lesions, the preoperative diagnosis by CBCT was of a cyst whereas the histological result was of chronic periapical granuloma. These results suggest that CBCT could be a rapid diagnostic method without invasive surgery and/or prolonged periods of observation to see if a nonsurgical therapy is effective.

Knowledge of the regional anatomy, such as, for example, root divergence and position in relation to the maxillary sinus or inferior alveolar nerve, and erosion of the vestibular and/or palatine/lingual cortical plate, can determine the surgical approach when planning periapical surgical treatment (**Figures 6** and **7**). After performing a descriptive study using CBCT to visualize the regional anatomy of the area of the upper first molars, Rigolone et al. [37] suggested the possibility of using a small vestibular access for apicoectomy of the palatal root of the maxillary first molars.

**2.2. Periapical disease**

176 Computed Tomography - Advanced Applications

nasal floor (arrows).

0.006 and 0.012 μSv [31].

Conventional radiographic techniques provide limited information about the origin, size, and situation of periapical lesions [28]. Superposition of adjacent anatomical and dental structures makes it necessary to perform a number of images from different angles [29]. It should be noted that the effective dose of radiation of two periapical radiographs in the area of the molars is of between 0.01 and 0.02 μSv [30], whereas the dose with limited CBCT is between

**Figure 5.** Supernumerary teeth in the anterior portion of the upper jaw. (a) Cone beam computed tomography (CBCT) reconstruction obtained with I-CAT system (Imaging Sciences International, Hatfield, PA, USA); (b) cross-sectional view of the supernumerary teeth and their relationship with adjacent anatomic structures. Notice a crown erupting in the

Experimental studies have shown that CBCT is superior to digital or conventional intraoral radiography for the detection of chemically [32] or mechanically [33] induced periapical lesions. Lofthag-Hansen et al. [29] demonstrated the utility of limited CBCT for the detection of periapical pathosis not identified by conventional intraoral radiography. With CBCT, these authors found a larger number of teeth and roots involved and a larger number of lesions extending toward the maxillary sinus than on periapical radiographs. In 70% of the cases studied, the examiners considered that CBCT provided relevant additional diagnostic information in comparison with intraoral radiographs. The authors recommend the use of CBCT when there is a clinical suspicion of periapical disease and no pathology is detected on conventional radiographic techniques, as well as to plan periapical surgery for multi-rooted teeth. On the same subject, Estrela et al. [34] demonstrated that panoramic and periapical radiographs underestimated both the number and size of periapical lesions in comparison with CBCT. Estrela et al. [35] compared CBCT and intraoral radiographs for the diagnosis of periapical pathology in 596 patients with one or more endodontically treated teeth. Periapical pathology was detected in

**Figure 6.** Well-defined radiolucent lesion at the apex of the lower right first molar. (a) Panoramic reconstruction of the CBCT. Two-dimensional measurement of lesion size (blue lines). (b, c) Measurement of the lesion in the axial and coronal sections.

**Figure 7.** Preoperative evaluation of the lower right quadrant for dental implants treatment. (a) Panoramic radiography. (b) Panoramic reconstruction from cone beam computed tomography (CBCT) obtained with I-CAT system (Imaging Sciences International, Hatfield, PA, USA). Notice a periapical radiolucency in the first upper right molar poorly seen in the panoramic radiography and better identified in the CBCT (arrows). (c–e) Multiplanar reconstruction showing the limits of the periapical lesion (circle) and buccal alveolar plate destruction (arrow). (f) Three-dimensional-rendered model for case illustration.

In any case, there appears to be a degree of agreement by authors that CBCT should be reserved for those cases in which conventional radiological techniques are insufficient for providing diagnostic information about periapical pathosis.

#### **2.3. Medication-related osteonecrosis of the jaws (MRONJs)**

Medication-related osteonecrosis of the jaw (MRONJ) due to bisphosphonates was described by Marx in 2003 [38] and is characterized by exposure of the bone in the maxillofacial area (which can occur spontaneously or after a dental intervention) occurring in patients treated with antiresortives or antiangiogenics and that does not heal after 8 weeks. The diagnosis of MRONJ is based on clinical and/or radiological findings. The differential diagnosis includes lesions secondary to radiotherapy of the head and neck and malignant diseases of the jaw. Radiological evaluation is used to confirm the diagnosis and determine the extent of the lesions. The radiological study must include orthopantomography (OPG) as first-line test, reserving magnetic resonance imaging (MRI), CT, and CBCT for those cases that require complementary tests to resolve the differential diagnosis [39]. A number of radiological signs suggestive of ONJ have been described, including an absence of bone healing and osteosclerosis at the cortical margins of dental sockets after tooth extraction, broadening of the periodontal ligament, osteolysis, altered medullary bone structure with increased density, and the formation of sequestra [40, 41] (**Figure 8**).

CBCT, as an alternative to CT, has become more widely accepted as a diagnostic technique for 3D imaging in jaw lesions [42, 43]. Although soft-tissue definition can be limited due to a poor contrast resolution, CBCT can provide detailed information about cortical thickness, medullary involvement, irregularities after tooth extraction, and density of the medullary bone; its use has been described in the diagnosis, follow-up, and treatment of patients with

In any case, there appears to be a degree of agreement by authors that CBCT should be reserved for those cases in which conventional radiological techniques are insufficient for

**Figure 7.** Preoperative evaluation of the lower right quadrant for dental implants treatment. (a) Panoramic radiography. (b) Panoramic reconstruction from cone beam computed tomography (CBCT) obtained with I-CAT system (Imaging Sciences International, Hatfield, PA, USA). Notice a periapical radiolucency in the first upper right molar poorly seen in the panoramic radiography and better identified in the CBCT (arrows). (c–e) Multiplanar reconstruction showing the limits of the periapical lesion (circle) and buccal alveolar plate destruction (arrow). (f) Three-dimensional-rendered

Medication-related osteonecrosis of the jaw (MRONJ) due to bisphosphonates was described by Marx in 2003 [38] and is characterized by exposure of the bone in the maxillofacial area (which can occur spontaneously or after a dental intervention) occurring in patients treated with antiresortives or antiangiogenics and that does not heal after 8 weeks. The diagnosis of MRONJ is based on clinical and/or radiological findings. The differential diagnosis includes lesions secondary to radiotherapy of the head and neck and malignant diseases of the jaw.

providing diagnostic information about periapical pathosis.

model for case illustration.

178 Computed Tomography - Advanced Applications

**2.3. Medication-related osteonecrosis of the jaws (MRONJs)**

**Figure 8.** Medication-associated osteonecrosis of the jaws (MROJ). (a) Amplification of the zone of interest in the panoramic reconstruction. (b) Sectional views of the CBCT where the presence of osteolytic lesion is observed with small bone sequestra formation (I-CAT Vision, Imaging Sciences International, Hatfield, PA, USA).

MRONJ [44, 45]. Fullmer et al. [46] described the radiological findings of chronic suppurative osteomyelitis of the mandible on CBCT, including two cases with a history of bisphosphonate use. The authors suggested that the information provided by CBCT was not only of diagnostic utility but also that it was useful for preoperative evaluation of the true extent of the medullary bone involvement, and this information was easily transferred to 3D models that served as topographical references for the surgical treatment.

Flisher et al. [45] and Pautke et al. [41] used CBCT to locate areas of osteolysis and bone sequestra for their subsequent analysis with fluorescent lamps (Wood's lamp) to direct tetracycline absorption-guided surgical debridement. MRONJ is usually diagnosed in advanced stages, when it starts to become symptomatic [47], and CBCT can therefore facilitate early diagnosis and the identification of sequestra that could be undetectable clinically or on panoramic radiographs. According to these authors, CBCT is a useful screening technique for ONJ in patients on treatment with bisphosphonates and with additional risk factors.

Barragan-Adjemian et al. [48] analyzed 26 cancer patients treated with intravenous bisphosphonates, 18 of them presenting exposure of necrotic bone. CBCT revealed sclerotic and radiolucent bone lesions, and it was possible to measure them. The authors suggested that CBCT examination can be useful for evaluation of the extent of the lesions and for patient follow-up. Treister et al. [49] compared clinical and radiographic features of a series of seven subjects with MRONJ who were evaluated by both CBCT and panoramic radiography. Radiographic findings included sclerosis, cortical irregularity, lucency, mottling, fragmentation/sequestra formation, sinus communication, and persistent sockets. CBCT demonstrated a greater extent and quality of changes compared with panoramic radiography in nearly all cases. Other authors suggested that staging of osteonecrosis of the jaw requires computed tomography for accurate definition of the extent of bony disease [50]. Kämmerer et al. [51] have shown significant advantage of CBCT over panoramic radiography for surgeons with regard to therapeutic planning for MRONJ.

### **2.4. Oral cancer**

The preoperative study of patients with oral cancer usually includes physical examination, blood tests, panendoscopy, and radiological examination. The radiological studies of choice are OPG, CT, and MRI. The technique of choice for visualization of tumor size in the soft tissues and for evaluation of cervical lymph node involvement is MRI, while CT is the technique of choice for evaluation of the presence and extent of bone invasion. The introduction of CBCT represents an alternative for the preoperative study of patients with oral cancer to evaluate the extent of jaw bone invasion.

Closmann and Schmidt [52] described the use of CBCT as a complementary examination for the preoperative evaluation of three patients with malignant lesions of the oral cavity (two squamous cell carcinomas and one osteosarcoma). Examination by CBCT was superior to that of OPG and MRI for evaluation of mandibular invasion and the extent of the lesion in the hard tissues, with the added advantage of lower cost and lower radiation dose than CT. The authors concluded that CBCT could be useful for the preoperative staging of oral cancer and for determining the extent of surgical resection necessary, as well as for planning reconstruction techniques.

In a study of 197 patients diagnosed with oral cancer, Linz et al. [53] have found that CBCT and bone scintigraphy (BS) showed the highest accuracy for the detection of bone invasion and showed better performance than panoramic radiography and CT/MRI. The authors concluded that for the evaluation of bone invasion, CBCT and BS might be the modalities of choice. However, CT and/or MRI remain essential for lymph node staging and for the detection of soft-tissue involvement.

### **3. Conclusions**

MRONJ [44, 45]. Fullmer et al. [46] described the radiological findings of chronic suppurative osteomyelitis of the mandible on CBCT, including two cases with a history of bisphosphonate use. The authors suggested that the information provided by CBCT was not only of diagnostic utility but also that it was useful for preoperative evaluation of the true extent of the medullary bone involvement, and this information was easily transferred to 3D models that served

Flisher et al. [45] and Pautke et al. [41] used CBCT to locate areas of osteolysis and bone sequestra for their subsequent analysis with fluorescent lamps (Wood's lamp) to direct tetracycline absorption-guided surgical debridement. MRONJ is usually diagnosed in advanced stages, when it starts to become symptomatic [47], and CBCT can therefore facilitate early diagnosis and the identification of sequestra that could be undetectable clinically or on panoramic radiographs. According to these authors, CBCT is a useful screening technique for

Barragan-Adjemian et al. [48] analyzed 26 cancer patients treated with intravenous bisphosphonates, 18 of them presenting exposure of necrotic bone. CBCT revealed sclerotic and radiolucent bone lesions, and it was possible to measure them. The authors suggested that CBCT examination can be useful for evaluation of the extent of the lesions and for patient follow-up. Treister et al. [49] compared clinical and radiographic features of a series of seven subjects with MRONJ who were evaluated by both CBCT and panoramic radiography. Radiographic findings included sclerosis, cortical irregularity, lucency, mottling, fragmentation/sequestra formation, sinus communication, and persistent sockets. CBCT demonstrated a greater extent and quality of changes compared with panoramic radiography in nearly all cases. Other authors suggested that staging of osteonecrosis of the jaw requires computed tomography for accurate definition of the extent of bony disease [50]. Kämmerer et al. [51] have shown significant advantage of CBCT over panoramic radiography for surgeons with regard to therapeutic planning for MRONJ.

The preoperative study of patients with oral cancer usually includes physical examination, blood tests, panendoscopy, and radiological examination. The radiological studies of choice are OPG, CT, and MRI. The technique of choice for visualization of tumor size in the soft tissues and for evaluation of cervical lymph node involvement is MRI, while CT is the technique of choice for evaluation of the presence and extent of bone invasion. The introduction of CBCT represents an alternative for the preoperative study of patients with oral cancer to evaluate

Closmann and Schmidt [52] described the use of CBCT as a complementary examination for the preoperative evaluation of three patients with malignant lesions of the oral cavity (two squamous cell carcinomas and one osteosarcoma). Examination by CBCT was superior to that of OPG and MRI for evaluation of mandibular invasion and the extent of the lesion in the hard tissues, with the added advantage of lower cost and lower radiation dose than CT. The authors concluded that CBCT could be useful for the preoperative staging of oral cancer and for determining the

extent of surgical resection necessary, as well as for planning reconstruction techniques.

ONJ in patients on treatment with bisphosphonates and with additional risk factors.

as topographical references for the surgical treatment.

180 Computed Tomography - Advanced Applications

**2.4. Oral cancer**

the extent of jaw bone invasion.

The introduction of CBCT represents a great technological advance in the context of oral and maxillofacial radiology as it permits the acquisition of high-quality 3D images and dynamic navigation over an area of interest in real time, with a short scan time and lower dose of radiation than conventional CT. The initial indications of CBCT have been extended by the progressive addition of new ones such as evaluation of the extent of osteonecrotic lesions of the jaw due to bisphosphonates, preoperative staging of oral cancer, and planning reconstructive surgery. As a consequence, this radiological technique represents an interesting complement to conventional radiology in those clinical situations in which 3D imaging can facilitate diagnosis and/or treatment.

### **Author details**

Márcio Diniz-Freitas\*, Javier Fernández-Feijoo, Lucía García-Caballero, Maite Abeleira, Mercedes Outumuro, Jacobo Limeres-Pose and Pedro Diz-Dios

\*Address all correspondence to: marcio.diniz@usc.es

Special Needs Unit and OMEQUI Research Group, School of Medicine and Dentistry, Santiago de Compostela University, Santiago de Compostela, Galicia, Spain

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**Physical Sciences, Engineering and Technology**

## **Novelty Detection‐Based Internal Fingerprint Segmentation in Optical Coherence Tomography Images**

Rethabile Khutlang, Pheeha Machaka, Ann Singh and Fulufhelo Nelwamondo

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67594

#### Abstract

Biometric fingerprint scanners scan the external skin's features onto a 2-D image. The performance of the automatic fingerprint identification system suffers first and foremost if the finger skin is wet, worn out or a fake fingerprint is used. We present an automatic segmentation of the papillary layer method, from images acquired using contact-less 3-D swept source optical coherence tomography (OCT). The papillary contour represents the internal fingerprint, which does not suffer from the external finger problems. It is embedded between the upper epidermis and papillary layers. Speckle noise is first reduced using non-linear filters from the slices composing the 3-D image. Subsequently, the stratum corneum is used to extract the epidermis. The epidermis, with its depth known, is used as the target class of the ensuing novelty detection. The outliers resulting from novelty detection represent the papillary layer. The contour of the papillary layer is segmented as the boundary between target and rejection classes. Using a mixture of Gaussian's novelty detection routine on images pre-processed with a regularized anisotropic diffusion filter, the papillary contours—internal fingerprints—are consistent with those segmented manually, with the modified Williams index above 0.9400.

Keywords: biometrics, novelty detection, segmentation, internal fingerprint, optical coherence tomography (OCT)

### 1. Introduction

Biometric identification uses identifiers unique to individuals; because of that, it edges out token-based and knowledge-based identification systems on safety and reliability. Individuals

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

can be described using biometric identifiers provided that they are sufficiently different for a population. Usable biometric identifiers should be easy to acquire; the acquired measurement should be in a form conducive to the extraction of the descriptive features. Extraction should preferably not be intrusive to an individual. They should be extractable on the whole population using the identification system. Fingerprints are popular biometric identifiers for identifying and authenticating individuals. Of all identifiers, fingerprints perform competitively on the factors used in assessing the suitability of any trait [1].

The external skin of the palm finger consists of a series of ridges and furrows, whose pattern determines the fingerprint's uniqueness. Local ridge characteristics that occur at the ridge's bifurcation and ending contribute to this uniqueness. Old age, disease or manual labour can depreciate the fingerprint's uniqueness if the ridges are worn out.

The external finger skin is the interface between an individual and a fingerprint recognition system. The performance of such systems depends on the conditions of the external finger skin. It suffers if the skin is scarred, wet, worn out or if a fake fingerprint is used [2]. Furthermore, standard 2-D readers capture the fingerprint onto a glass surface or a fingerprint paper card in the case of ink-based offline methods. To obtain the 2-D fingerprint image, the subject has to press their finger against a surface. The performance of a fingerprint recognition system using such contact-based acquisition is again negatively affected by the pressure exerted by the finger when making contact with the surface [3]. The pressure is usually non-uniform and results in captured 2-D images that have non-linear distortions. Lastly, 2-D imaging and signal processing of surface topology of a finger do not protect bypassing such systems by a fake fingerprint, which has the third dimension in depth [4].

The internal structure of a finger, the papillary layer, can be used to represent a fingerprint to alleviate the problems associated with the external skin's ridges and valleys. Actually, the papillary layer is the source of the fingerprint structure. It is the blueprint of the visible fingerprint undulations. During development, the basal layer of the epidermis grows faster than the two layers beneath and on top of it, the dermis and upper epidermis layers [5]. Pressure causes the basal layer to deform into the folds pattern that stays with an individual forever. That folds pattern forms an internal fingerprint; it is protected because it is inside the skin, and hence, it cannot be destroyed by superficial skin cuts. The fingerprint recognition system that uses such a fingerprint cannot be fooled by fake fingerprints as fake fingerprints are superficial to finger skin whereas the fingerprint at the papillary layer is beneath the epidermis. Manapuram et al. [6] proposed using optical coherence tomography (OCT) to image the three-dimensional structure of a finger to a depth that reaches the papillary layer of the finger. The internal fingerprint embedded between the upper epidermis and papillary layers is used for identification, instead of the surface fingerprint. Additionally, since OCT is contact-less, that fingerprint does not suffer distortions caused by the finger when making contact with the scanner.

A typical fingerprint recognition system is made up of sensing and acquisition, image enhancement, feature extraction, matching and decision-making components. Since the internal fingerprint is the blueprint to the external skin ridges and folds, the same recognition pipeline is applied. This chapter is focused on segmentation of the internal fingerprint, the papillary layer, from swept source optical coherence tomography (SS-OCT) 3-D images. The tissue beneath the surface has been imaged using time domain OCT for biometrics before [4, 6], while in the Fourier domain OCT, swept source OCT is preferred over spectral domain OCT as it minimizes dispersion and speckle effects better [7, 8]. In Ref. [9], spectral domain OCT was used to extract intricate biometric details such as the distribution of sweat pores and the pattern of the capillary bed and on the other hand, Zam et al. [10] used correlation mapping OCT.

Over a pre-determined depth range, Refs. [8] and [9] averaged XY cross-sectional images to project a 3-D image to 2-D image to segment the internal fingerprint. The fingertip curvature is removed by detecting points at the boundary between air and tissue in Ref. [10]. The points are then aligned to a straight line and concatenated to form a 2-D fingerprint. Akbari and Sadr [11] used vertical gradient thresholding to segment the external fingerprint from an artificial dummy covering it; this was an implicit segmentation of the internal fingerprint. Column accumulation functions are used to segment the internal fingerprint in Ref. [12]; they actually sample the three-dimensional contour of the papillary layer.

This chapter presents the pipeline to segment the internal fingerprint. The method preserves the curvature of the papillary layer. First, the cross-sectional images of the 3-D OCT image are filtered to reduce the effects of speckle noise. Then, the multilevel image thresholds the Otsu segmentation method [13], which is used to detect the outermost skin layer from each filtered slice. The stratum corneum, the outermost skin layer, is used to estimate the extent of the epidermis. The epidermis forms the target data of the ensuing novelty detection, which is applied to image slices, and the boundary to the outlier objects is the contour of the papillary layer—the internal fingerprint. The segmented internal fingerprint has the 3-D profile features that 2-D fingerprints' pattern loses [14]. OCT does not suffer the problem of typical 2-D acquisitions, where variance in pressure exerted to acquire 2-D fingerprints results in deviations in the features extracted from each acquisition on the same finger.

### 2. Materials and methods

can be described using biometric identifiers provided that they are sufficiently different for a population. Usable biometric identifiers should be easy to acquire; the acquired measurement should be in a form conducive to the extraction of the descriptive features. Extraction should preferably not be intrusive to an individual. They should be extractable on the whole population using the identification system. Fingerprints are popular biometric identifiers for identifying and authenticating individuals. Of all identifiers, fingerprints perform competitively on the

The external skin of the palm finger consists of a series of ridges and furrows, whose pattern determines the fingerprint's uniqueness. Local ridge characteristics that occur at the ridge's bifurcation and ending contribute to this uniqueness. Old age, disease or manual labour can

The external finger skin is the interface between an individual and a fingerprint recognition system. The performance of such systems depends on the conditions of the external finger skin. It suffers if the skin is scarred, wet, worn out or if a fake fingerprint is used [2]. Furthermore, standard 2-D readers capture the fingerprint onto a glass surface or a fingerprint paper card in the case of ink-based offline methods. To obtain the 2-D fingerprint image, the subject has to press their finger against a surface. The performance of a fingerprint recognition system using such contact-based acquisition is again negatively affected by the pressure exerted by the finger when making contact with the surface [3]. The pressure is usually non-uniform and results in captured 2-D images that have non-linear distortions. Lastly, 2-D imaging and signal processing of surface topology of a finger do not protect bypassing such systems by a fake

The internal structure of a finger, the papillary layer, can be used to represent a fingerprint to alleviate the problems associated with the external skin's ridges and valleys. Actually, the papillary layer is the source of the fingerprint structure. It is the blueprint of the visible fingerprint undulations. During development, the basal layer of the epidermis grows faster than the two layers beneath and on top of it, the dermis and upper epidermis layers [5]. Pressure causes the basal layer to deform into the folds pattern that stays with an individual forever. That folds pattern forms an internal fingerprint; it is protected because it is inside the skin, and hence, it cannot be destroyed by superficial skin cuts. The fingerprint recognition system that uses such a fingerprint cannot be fooled by fake fingerprints as fake fingerprints are superficial to finger skin whereas the fingerprint at the papillary layer is beneath the epidermis. Manapuram et al. [6] proposed using optical coherence tomography (OCT) to image the three-dimensional structure of a finger to a depth that reaches the papillary layer of the finger. The internal fingerprint embedded between the upper epidermis and papillary layers is used for identification, instead of the surface fingerprint. Additionally, since OCT is contact-less, that fingerprint does not suffer distortions caused by the finger when making

A typical fingerprint recognition system is made up of sensing and acquisition, image enhancement, feature extraction, matching and decision-making components. Since the internal fingerprint is the blueprint to the external skin ridges and folds, the same recognition pipeline is applied. This chapter is focused on segmentation of the internal fingerprint, the

factors used in assessing the suitability of any trait [1].

190 Computed Tomography - Advanced Applications

fingerprint, which has the third dimension in depth [4].

contact with the scanner.

depreciate the fingerprint's uniqueness if the ridges are worn out.

A swept source OCT system (OCS1300SS, Thorlabs, USA) was used to capture the internal finger structure. The central wavelength of 1325 nm and spectral bandwidth of 100 nm were parameters of the swept laser optical source with an average power output of 10.0 mW. The source had an axial scan rate of 16 kHz. The OCT system had a maximum imaging depth of 3 mm. Scattering properties of a sample as a function of depth are contained in an A-scan for a fixed position of the scanned beam. A collection of A-scans results in a cross-sectional image (B-scan). The collection of B-scans results in a volumetric image as shown in Figure 1.

### 2.1. 3-D internal fingerprint segmentation

We use novelty detection machine learning techniques to separate the papillary junction from the upper epidermis. As can be seen in Figure 1, the human finger skin shows distinct regions when imaged with OCT. Corneum stratum is clearly visible as a high-pixel intensity

Figure 1. 3-D OCT scan made of 512 cross-sectional images at a human fingertip.

region due to its tissue scattering properties. The rest of the epidermis forms a different class altogether (hereupon referred to as the upper epidermis), with its low and uniform intensity pixels sandwiched between the stratum corneum and the papillary junction. The papillary junction is a distinct region with high-pixel intensity and internal fingerprint undulations clearly visible. We use the stratum corneum, Section 2.2, just to locate the extent of the low-pixel intensity epidermis region—the upper epidermis. This upper epidermis forms the one class in novelty detection that can be characterized and learnt, the target class. Our hypothesis is that the papillary junction pixels, being different in texture, will be classified as an outlier by a novelty detection routine trained using this low-pixel intensity upper epidermis region. The routines are trained using only such low-intensity pixel values but are expected to classify all pixels at a height lower than the low pixel's intensity region used for training. Figure 2 shows such a low-pixel intensity upper epidermis region used as a training set for novelty detection routines for a single cross-sectional image. This band of training data pixels is located using the stratum corneum edge. Pixels below this band (annotated by a green colour) are sent to novelty detection routines to classify as the target or the outlier.

A 3-D OCT scan is processed on a cross-sectional basis to segment the internal fingerprint. First, the cross sections are filtered to reduce speckle noise. Then, a threshold is applied to detect the stratum corneum. The stratum corneum is used to locate the upper epidermis, which in turn is used to train novelty detection routines to find the undulations of the papillary junction. The undulations of the papillary junction are the internal fingerprints; a 3-D fingerprint is found by concatenating the 2-D cross-sectional images. The workflow is illustrated in Figure 3. Below is the expansion of the speckle noise reduction, stratum corneum edge detection and the eventual novelty detection methods used as a papillary contour segmentation pipeline.

Novelty Detection‐Based Internal Fingerprint Segmentation in Optical Coherence Tomography Images http://dx.doi.org/10.5772/67594 193

Figure 2. A band located using the corneum stratum edge and used as a training set for novelty detection routines.

Figure 3. The internal fingerprint segmentation workflow.

### 2.2. Corneum stratum detection

region due to its tissue scattering properties. The rest of the epidermis forms a different class altogether (hereupon referred to as the upper epidermis), with its low and uniform intensity pixels sandwiched between the stratum corneum and the papillary junction. The papillary junction is a distinct region with high-pixel intensity and internal fingerprint undulations clearly visible. We use the stratum corneum, Section 2.2, just to locate the extent of the low-pixel intensity epidermis region—the upper epidermis. This upper epidermis forms the one class in novelty detection that can be characterized and learnt, the target class. Our hypothesis is that the papillary junction pixels, being different in texture, will be classified as an outlier by a novelty detection routine trained using this low-pixel intensity upper epidermis region. The routines are trained using only such low-intensity pixel values but are expected to classify all pixels at a height lower than the low pixel's intensity region used for training. Figure 2 shows such a low-pixel intensity upper epidermis region used as a training set for novelty detection routines for a single cross-sectional image. This band of training data pixels is located using the stratum corneum edge. Pixels below this band (annotated by a green colour) are sent to novelty detection routines to classify as the target

Figure 1. 3-D OCT scan made of 512 cross-sectional images at a human fingertip.

192 Computed Tomography - Advanced Applications

A 3-D OCT scan is processed on a cross-sectional basis to segment the internal fingerprint. First, the cross sections are filtered to reduce speckle noise. Then, a threshold is applied to detect the stratum corneum. The stratum corneum is used to locate the upper epidermis, which in turn is used to train novelty detection routines to find the undulations of the papillary junction. The undulations of the papillary junction are the internal fingerprints; a 3-D fingerprint is found by concatenating the 2-D cross-sectional images. The workflow is illustrated in Figure 3. Below is the expansion of the speckle noise reduction, stratum corneum edge detection and the eventual novelty detection methods used as a papillary contour segmentation

or the outlier.

pipeline.

As a pre-processing step, cross-sectional images of the 3-D OCT scan are filtered using the anisotropic diffusion - Perona and Malik's partial differential equations (PDE) - filter due to its soft-edge preservation characteristics [15]. The edges of the papillary junction undulations are soft. The heat equation (equivalent to the convolution of the signal with Gaussian's at each scale) with the signal as the initial datum u<sup>0</sup> is improved by the Perona and Malik filter by reformulating it as a non-linear equation of the porous medium type:

$$\frac{\partial \boldsymbol{u}}{\partial t} = \operatorname{div} \left( g(|\nabla \boldsymbol{u}|) \nabla \boldsymbol{u} \right), \boldsymbol{u}(0) = \ \boldsymbol{u}\_0 \tag{1}$$

In this equation, g is a smooth non-increasing function. Its regularized version was also applied as it is stable in the presence of speckle noise [16]. The stability brought about by Catté et al. [16] is due to the replacement of the gradient j∇uj by its estimate jDG<sup>σ</sup> � uj in the Perona and Malik model (1); G<sup>σ</sup> is a Gaussian function.

The two filters were compared to the total variation denoising technique, which performs denoising as an infinite-dimensional minimization problem [17]. Speckle noise results from the coherent nature of laser radiation and the interferometric detection of the scattered light [11]. To minimize speckle noise, [14] applied rotating kernel transformation, while [12] employed parallel processing to speed up median filtering to suppress speckle noise.

After the pre-processing step, we then segment the cross-sectional images using the two-image thresholds of the Otsu method to detect the stratum corneum edge. The filtered cross-sectional image forms an input to a non-parametric method of threshold selection. The filtered image pixels can be represented in L gray levels ½1, 2, …, L�, where we assume that there are two thresholds, 1 ≤ k<sup>1</sup> < k<sup>2</sup> < L, for separating an image into three classes. Otsu [13] introduced the discriminant criterion measures used in discriminant analysis to evaluate how strong a threshold is. In this case, segmentation is seen as an optimization problem to search for the two thresholds, k<sup>0</sup> <sup>1</sup> and k<sup>0</sup> <sup>2</sup>, that maximize the discriminant criterion measure σB<sup>2</sup> —a function of the two variables k<sup>1</sup> and k2:

$$
\sigma B^2(k'\_1, k'\_2) = \max\_{1 \le k\_1 < k\_2 < L} \sigma B^2(k\_1, k\_2) \tag{2}
$$

Thresholds are selected in a sequential search by using cumulative probabilities of class occurrence and class mean levels [13]. The highest threshold extracts the stratum corneum. The stratum corneum edge is represented by the topmost pixels of its perimeter.

#### 2.3. Novelty detection to segment papillary layer

Novelty detection is used as a segmentation method because the 3-D internal fingerprint is defined as the boundary between the upper epidermis pixels and the papillary layer pixels. Novelty detection is applied to cases where the class of objects that are not of interest, for example outliers, cannot be sufficiently modelled [18]. Only the upper epidermis pixels, the target class as shown by a green band in Figure 2 can be sufficiently modelled in this case. Novelty detection routines are trained to recognize the upper epidermal layer. The upper epidermal layer is extracted using the detected stratum corneum edge. According to Ref. [8], the epidermis extends to an average of 0.34 mm at the palm finger region. Epidermal pixel values, from a depth of 10 to that of 20 pixels from the stratum corneum edge, are used as objects of novelty detection routines. An example training dataset extracted using this procedure is shown in Figure 2 as a band of pixels annotated by a green colour. All pixels at a depth below the green band constitute the test set that is an input to a trained novelty detection routine. The aim is to train novelty detection techniques to recognize only the upper epidermis layer. The papillary layer would be the rejection region of this technique, with the papillary contour at the boundary between target and rejection (outlier) classes.

Gaussian, mixture of Gaussians (MoG), k-means and k nearest neighbour (kNN) routines are used. The target data are modelled as a Gaussian distribution when using a Gaussian routine. To create a more robust description of the target objects, MoG uses n Gaussians [19], where n is determined empirically. k-Means novelty detection technique describes the target dataset using k clusters. The cluster centres are placed using the standard k-means clustering procedure [19]. The kNN routine labels test objects by comparing them to target objects using the Euclidean distance [20].

Training novelty detection routines involve setting a percentage error a routine can make, that is, the number of target objects that may be misclassified as outliers on the training set. To train a Gaussian routine, the density estimate is avoided to minimize numerical instabilities, and just the Mahalanobis distance is used:

After the pre-processing step, we then segment the cross-sectional images using the two-image thresholds of the Otsu method to detect the stratum corneum edge. The filtered cross-sectional image forms an input to a non-parametric method of threshold selection. The filtered image pixels can be represented in L gray levels ½1, 2, …, L�, where we assume that there are two thresholds, 1 ≤ k<sup>1</sup> < k<sup>2</sup> < L, for separating an image into three classes. Otsu [13] introduced the discriminant criterion measures used in discriminant analysis to evaluate how strong a threshold is. In this case, segmentation is seen as an optimization problem to search for the two

<sup>2</sup>, that maximize the discriminant criterion measure σB<sup>2</sup>

σB<sup>2</sup>

<sup>2</sup>Þ ¼ max 1 ≤ k1<k2<L

The stratum corneum edge is represented by the topmost pixels of its perimeter.

contour at the boundary between target and rejection (outlier) classes.

Thresholds are selected in a sequential search by using cumulative probabilities of class occurrence and class mean levels [13]. The highest threshold extracts the stratum corneum.

Novelty detection is used as a segmentation method because the 3-D internal fingerprint is defined as the boundary between the upper epidermis pixels and the papillary layer pixels. Novelty detection is applied to cases where the class of objects that are not of interest, for example outliers, cannot be sufficiently modelled [18]. Only the upper epidermis pixels, the target class as shown by a green band in Figure 2 can be sufficiently modelled in this case. Novelty detection routines are trained to recognize the upper epidermal layer. The upper epidermal layer is extracted using the detected stratum corneum edge. According to Ref. [8], the epidermis extends to an average of 0.34 mm at the palm finger region. Epidermal pixel values, from a depth of 10 to that of 20 pixels from the stratum corneum edge, are used as objects of novelty detection routines. An example training dataset extracted using this procedure is shown in Figure 2 as a band of pixels annotated by a green colour. All pixels at a depth below the green band constitute the test set that is an input to a trained novelty detection routine. The aim is to train novelty detection techniques to recognize only the upper epidermis layer. The papillary layer would be the rejection region of this technique, with the papillary

Gaussian, mixture of Gaussians (MoG), k-means and k nearest neighbour (kNN) routines are used. The target data are modelled as a Gaussian distribution when using a Gaussian routine. To create a more robust description of the target objects, MoG uses n Gaussians [19], where n is determined empirically. k-Means novelty detection technique describes the target dataset using k clusters. The cluster centres are placed using the standard k-means clustering procedure [19]. The kNN routine labels test objects by comparing them to target objects using the

Training novelty detection routines involve setting a percentage error a routine can make, that is, the number of target objects that may be misclassified as outliers on the training set. To train

—a function of the

ðk1, k2Þ (2)

thresholds, k<sup>0</sup>

<sup>1</sup> and k<sup>0</sup>

194 Computed Tomography - Advanced Applications

σB<sup>2</sup> ðk 0 <sup>1</sup>, k 0

2.3. Novelty detection to segment papillary layer

two variables k<sup>1</sup> and k2:

Euclidean distance [20].

$$f(\mathbf{x}) = (\mathbf{x} - \boldsymbol{\mu})^T \sum^{-1} (\mathbf{x} - \boldsymbol{\mu}) \tag{3}$$

The distance fðxÞ of a test object x from the mean of the target data; the novelty detection routine is defined as:

$$h(\mathbf{x}) = \begin{cases} \text{target} & \text{if } |f(\mathbf{x}) \le \theta \\ \text{outlier if } f(\mathbf{x}) > \theta \end{cases} \tag{4}$$

The mean μ and covariance matrix ∑ are just training set estimates, and the threshold θ is based on the percentage error a routine is allowed to make [21]. An object is labelled a target object if its distance from mean is less than the set threshold and labelled an outlier otherwise. Training MoG and k-means routines involve determining the number of Gaussians and clusters, respectively, to optimally represent the training data. The leave-one-out cross-validation error is used to optimize k for the kNN routine on the training dataset.

The same percentage error is set during the training of different routines to compare performance on a test set. The function derived using the set percentage error is used to map pixels (extracted at a depth higher than the section used for training) as a target or an outlier on each cross section of the 3-D image. For each cross-sectional image of a 3-D OCT scan, pixels below the green band, as in Figure 2, are objects to be classified as either the target or the outlier. Objects/pixels classified as target objects are labelled one and as outliers, labelled zero. The labels are translated back to the object/pixel coordinates; and the papillary contour is an edge between the zero- and the one-labelled regions of an image. The papillary layer contour is the boundary between the target (upper epidermis) and rejection (papillary layer) classes. The 3-D papillary contour is obtained by concatenating the detected 2-D contours together. The procedure is shown in Algorithm 1.

#### Algorithm 1. Algorithm to segment an internal fingerprint

Input = 512 cross sections output = [] for all i in length(input) do this\_cross\_sec = input(i) denoised\_im = filter(this\_cross\_sec) c\_s = corneum-stratum-detect(denoised\_im) train\_data = denoised\_im(c\_s +10: c\_s + 20) trained\_routine = novelty-detection-routine(train\_data, fraction\_reject) test\_im = denoised\_im(c\_s + 21: length(denoised\_im))

```
test_im_labels = map-labels(test_im * trained_routine)
papillary_contour = perimeter-rejection-class(test_im_labels)
output = concatenate(output, papillary_contour)
```
#### end for

#### 2.4. Evaluation of the segmented papillary contour

Papillary contours were outlined manually from the slices composing the 3-D image. The manual outlines represented the gold standard used in assessing the performance of different routines. The agreement between the gold standard papillary contours and those segmented automatically was assessed using the Hausdorff distance [22] and the modified Williams index (MWI) [23]. The MWI specifies whether the contour outlined by routine 0 agrees with the set of n manual contours as much as a manual contour agrees with another contour from the manual set; it is defined as:

$$MWI = \frac{\frac{1}{n} \sum\_{j=1}^{n} \frac{1}{D\_{0j}}}{\frac{2}{n(n-1)} \sum\_{j=1}^{n} \sum\_{j'=j+1}^{n} \frac{1}{D\_{jj'}}} \tag{5}$$

where

$$D\_{\vec{\eta}\prime} = \frac{1}{N} \sum\_{i=1}^{N} H(\mathbf{x}\_{\vec{\eta}\prime}, \mathbf{x}\_{\vec{\eta}\prime}) \tag{6}$$

Djj<sup>0</sup> denotes the agreement between two observers j and j 0 . xij denotes observer j outlining image i and Hðx, yÞ is the Hausdorff distance between images contours x and y.

### 3. Results

The two-image thresholds of the Otsu method were determined automatically for each cross section. The input to the two-image thresholds Otsu segmentation method was the denoised cross-sectional image. The output was the exterior edge of the stratum corneum. Each denoising technique pronounced pixel intensities of the stratum corneum layer differently; the Otsu method was able to detect the change in the gradient between the stratum corneum layer and air. Figure 4 shows the detected edge for the three denoising routines that were used.

The objects used to train novelty detection routines had one feature, pixel intensity value of the unit 8 cross-sectional image. The pixels were extracted at 10 pixel depth from the stratum corneum contour detected using the two image thresholds Otsu method. A set of 50 YZ crosssectional scans was used to study the agreement between papillary contours segmented by two researchers and the novelty detection routines. The comparisons were made using the Hausdorff distance. T11 and T12 represent the first observer, outlining the papillary contours

Novelty Detection‐Based Internal Fingerprint Segmentation in Optical Coherence Tomography Images http://dx.doi.org/10.5772/67594 197

test\_im\_labels = map-labels(test\_im \* trained\_routine)

2.4. Evaluation of the segmented papillary contour

MW I ¼

Djj<sup>0</sup> denotes the agreement between two observers j and j

Papillary contours were outlined manually from the slices composing the 3-D image. The manual outlines represented the gold standard used in assessing the performance of different routines. The agreement between the gold standard papillary contours and those segmented automatically was assessed using the Hausdorff distance [22] and the modified Williams index (MWI) [23]. The MWI specifies whether the contour outlined by routine 0 agrees with the set of n manual contours as much as a manual contour agrees with another contour from the manual

> 1 n X<sup>n</sup> j¼1 1 D0<sup>j</sup>

i¼1

The two-image thresholds of the Otsu method were determined automatically for each cross section. The input to the two-image thresholds Otsu segmentation method was the denoised cross-sectional image. The output was the exterior edge of the stratum corneum. Each denoising technique pronounced pixel intensities of the stratum corneum layer differently; the Otsu method was able to detect the change in the gradient between the stratum corneum layer and air. Figure 4 shows the detected edge for the three denoising routines that were used. The objects used to train novelty detection routines had one feature, pixel intensity value of the unit 8 cross-sectional image. The pixels were extracted at 10 pixel depth from the stratum corneum contour detected using the two image thresholds Otsu method. A set of 50 YZ crosssectional scans was used to study the agreement between papillary contours segmented by two researchers and the novelty detection routines. The comparisons were made using the Hausdorff distance. T11 and T12 represent the first observer, outlining the papillary contours

X<sup>n</sup>�<sup>1</sup> j¼1 X<sup>n</sup> j 0 ¼jþ1 1 Djj<sup>0</sup> (5)

Hðxij, xij0Þ (6)

. xij denotes observer j outlining

0

2 nðn�1Þ

Djj<sup>0</sup> <sup>¼</sup> <sup>1</sup> N X N

image i and Hðx, yÞ is the Hausdorff distance between images contours x and y.

output = concatenate(output, papillary\_contour)

196 Computed Tomography - Advanced Applications

end for

set; it is defined as:

where

3. Results

papillary\_contour = perimeter-rejection-class(test\_im\_labels)

Figure 4. A raw cross-sectional image (a) together with the corneum stratum edge overlaid on its filtered version using anisotropic diffusion (b), its regularized version (c) and the total variation denoising technique (d).

for the first and second time. T2 represents the second observer, while Gau, MoG, KM and kNN represent Gaussian, mixture of Gaussians, k-means and k nearest neighbour routines respectively. The agreement between contours outlined by an observer and between observers is shown in Table 1.

The Hausdorff distance was used to determine both the number of Gaussians and clusters to use from the 50 scans. A plot of the Hausdorff distance as a function of the number of Gaussians or clusters is shown in Figure 5. Three Gaussians were used with the mixture of Gaussians, and three clusters were used with the k-means routine. k was optimized using the leave-one-out cross-validation for each cross-sectional image segmentation using the kNN routine.

The Hausdorff distance was used to obtain the MWI for comparing computer-generated contours to hand-drawn ones. The MWI is the ratio between the average computer-observer


Table 1. Comparison of manual papillary segmentation between two observers.

agreement and the average observer-observer agreement. Contours outlined by two volunteers constituted four manual observations per object. Table 2 shows the agreement between the volunteers and novelty detection routines in segmenting anisotropic diffusion filtered scans and the MWI of the routines, together with the 95% confidence interval estimate for the MWI, assuming a standard normal distribution. Table 3 shows the evaluation of the novelty

Figure 5. Hausdorff distance as a function of the number of Gaussians for MoG and clusters for k-means.


Table 2. Comparison between manual papillary segmentation and segmentation using novelty detection techniques on anisotropic filtered images.


Table 3. Comparison between manual papillary segmentation and segmentation using novelty detection techniques on regularized anisotropic filtered images.


detection segmentation techniques with the regularized anisotropic diffusion filtered images as the input, while Table 4 shows that of total variation filtered images as input.

agreement and the average observer-observer agreement. Contours outlined by two volunteers constituted four manual observations per object. Table 2 shows the agreement between the volunteers and novelty detection routines in segmenting anisotropic diffusion filtered scans and the MWI of the routines, together with the 95% confidence interval estimate for the MWI, assuming a standard normal distribution. Table 3 shows the evaluation of the novelty

Figure 5. Hausdorff distance as a function of the number of Gaussians for MoG and clusters for k-means.

anisotropic filtered images.

198 Computed Tomography - Advanced Applications

regularized anisotropic filtered images.

Gau 4.7554 0.4355 4.7282 0.3832 0.9450 (0.9416, 0.9485) MoG 4.7262 0.3823 4.7111 0.4111 0.9498 (0.9465, 0.9530) KM 4.7627 0.4917 4.7920 0.4914 0.9386 (0.9353, 0.9420) kNN 4.7664 0.4053 4.7118 0.4271 0.9455 (0.9421, 0.9489)

Table 2. Comparison between manual papillary segmentation and segmentation using novelty detection techniques on

Gau 4.7113 0.4091 4.7302 0.4106 0.9504 (0.9474, 0.9535) MoG 4.680 60.3934 4.7088 0.3598 0.9548 (0.9518, 0.9578) KM 4.7350 0.4038 4.7435 0.4028 0.9473 (0.9442, 0.9505) kNN 4.7295 0.3667 4.7631 0.3678 0.9474 (0.9445, 0.9502)

Table 3. Comparison between manual papillary segmentation and segmentation using novelty detection techniques on

T11 and AL T21 and Al MWI Confidence interval

T11 and AL T21 and Al MWI Confidence interval

Mixture of Gaussians had the best overall performance in segmenting the papillary contour across the three denoising techniques. For each denoising technique, the papillary contour segmented using the MoG has been overlaid and compared with a manual papillary outline for that cross section in Figure 6. Novelty detection techniques generally struggled to segment the papillary contour from scans pre-processed using the total variation denoising technique. The 3-D papillary contour segmented using the worst performing novelty detection routine, k-means, on total variation denoised scans is shown in Figure 7, side by side with the same

Figure 6. A raw cross-sectional image with papillary contour manually outlined (a) together with the overlaid papillary contour segmented using the MoG routine when that cross section is pre-processed using anisotropic diffusion (b), its regularized version (c) and the total variation denoising technique (d).

Table 4. Comparison between manual papillary segmentation and segmentation using novelty detection techniques on total variation filtered images.

scan segmented using the MoG routine when pre-processed using the regularized anisotropic diffusion filter, the best performing workflow.

Figure 7. A 3-D papillary contour segmented using the k-means routine on a scan pre-processed using the total variation technique (a), side by side with the same scan pre-processed with regularized anisotropic diffusion and segmented using MoG.

### 4. Discussion

The aim of our chapter was to segment the internal fingerprint from swept source optical coherence tomography 3-D scans. This forms one component of the internal fingerprint recognition system that uses an OCT scanner as a contact-less acquisition device. The system is composed of the following components: sensing, 3-D internal fingerprint segmentation, feature extraction, matching and decision-making components. We use an SS-OCT system as a sensing component. The feature extraction and subsequent components have not been implemented.

No evaluation of internal fingerprint segmentation was found in the literature for direct comparison with our results. An edge-based segmentation technique was applied to detect an artificial layer glued to a fingertip in Ref. [11]. They used vertical gradient edge detection technique, where the dummy fingerprint was glued to the fingertip and the method marked out the border between the real skin and the artificial layer. However, the segmented border was subjectively evaluated.

Both Refs. [8] and [9] averaged XY cross-sectional images of a 3-D OCT scan to obtain the 2-D internal fingerprint image. Lui and Buma [9] had removed the overall fingertip curvature without affecting the fine-scale undulation of the friction ridge by fitting a third-order polynomial to the stratum corneum edge. We deduce that their resultant 2-D internal fingerprint was more accurate than that of Ref. [8] because the rectangle selected to average across cut more evenly across the papillary region for the straightened fingertip rather than the fingertip retaining the original curvature. They both did not perform quantitative evaluation of their XY averaging segmentation technique.

Sousedik et al. [12] segment an OCT scan of a fingertip into two 3-D fingerprint layers—the surface fingerprint and an internal one embedded between the upper epidermis and the papillary layers. However, they do not produce a continuous 3-D internal fingerprint layer but rather a scattered point cloud. This is the fundamental difference between their method and the one presented in this chapter, which produces a continuous 3-D surface of the internal fingerprint. They do not perform quantitative evaluation of the internal fingerprint segmentation but rather they evaluate the ability to detect the two layers of fingerprints; they got a 90% ability in the scans without anomalies related to subject finger motion.

scan segmented using the MoG routine when pre-processed using the regularized anisotropic

The aim of our chapter was to segment the internal fingerprint from swept source optical coherence tomography 3-D scans. This forms one component of the internal fingerprint recognition system that uses an OCT scanner as a contact-less acquisition device. The system is composed of the following components: sensing, 3-D internal fingerprint segmentation, feature extraction, matching and decision-making components. We use an SS-OCT system as a sensing component. The feature extraction and subsequent components have not been

Figure 7. A 3-D papillary contour segmented using the k-means routine on a scan pre-processed using the total variation technique (a), side by side with the same scan pre-processed with regularized anisotropic diffusion and segmented using

No evaluation of internal fingerprint segmentation was found in the literature for direct comparison with our results. An edge-based segmentation technique was applied to detect an artificial layer glued to a fingertip in Ref. [11]. They used vertical gradient edge detection technique, where the dummy fingerprint was glued to the fingertip and the method marked out the border between the real skin and the artificial layer. However, the segmented border

Both Refs. [8] and [9] averaged XY cross-sectional images of a 3-D OCT scan to obtain the 2-D internal fingerprint image. Lui and Buma [9] had removed the overall fingertip curvature without affecting the fine-scale undulation of the friction ridge by fitting a third-order polynomial to the stratum corneum edge. We deduce that their resultant 2-D internal fingerprint was more accurate than that of Ref. [8] because the rectangle selected to average across cut more evenly across the papillary region for the straightened fingertip rather than the fingertip retaining the original curvature. They both did not perform quantitative evaluation of their

Sousedik et al. [12] segment an OCT scan of a fingertip into two 3-D fingerprint layers—the surface fingerprint and an internal one embedded between the upper epidermis and the

diffusion filter, the best performing workflow.

200 Computed Tomography - Advanced Applications

4. Discussion

MoG.

implemented.

was subjectively evaluated.

XY averaging segmentation technique.

We quantitatively evaluated the performance of the internal fingerprint segmentation method that is proposed [24]. Aside from evaluating performance of the proposed segmentation procedure, using the internal fingerprint has benefits over the surface fingerprint. It is more difficult to spoof automated fingerprint identification systems that use an internal fingerprint. Substrates that are used to make fake fingerprints (gelatin, silicon, waxes of difference concentration) have varying scattering properties. Even those with scattering properties close to those of human fingers (polydimethylsiloxane mixed with titanium oxide [9]) have a problem in that the OCT will reveal a stratum corneum layer of abnormal thickness. The proposed segmentation method uses the fact that the epidermis extends to an average of 0.34 mm at the palm finger region [9]; it can be adapted to raise an alert if an internal fingerprint is not detected within an expected range. Furthermore, using the internal fingerprint minimizes the impact of fingerprint surface cuts, but deep cuts will still present a problem.

An advantage of extracting features from a 3-D internal fingerprint is that the 2-D (flat) fingerprint pattern loses the 3-D profile features that also provide information that can be used to uniquely identify an individual [14]. The automated fingerprint identification system that uses OCT as a sensor includes all of the 2-D morphological features, along with the 3-D profile which will increase discrimination performance. Performance comparisons will be made by using extended 2-D minutiae features in the 3-D space to include height and angle information and by using finger surface codes as 3-D features [25]. Figure 8 shows the internal and external fingerprint of the same finger—the external one is a conventional 2-D optical scan that is cropped to correspond to the OCT-scanned internal one. We propose that an eventual recognition performance of the system being developed will be an improvement over conventional

Figure 8. The image on the left is a conventional 2-D external fingerprint that has been cropped to an area corresponding to that scanned by the OCT, right image, of the same finger.

systems as physical deterioration of an external fingerprint will be countered by using the internal fingerprint.

Sousedik et al. [12] used a support vector machine to detect the layer that corresponds to a fake fingerprint glued to a fingertip, using the overall energy of the layers as a feature vector. They did not use machine learning for matching different fingertips but rather for detecting artefacts glued to fingertips. Kumar and Kwong [25] implemented matching the 3-D surface fingerprints obtained using a single camera, using both the finger surface code and 3-D minutiae as features. They got a better matching performance when combining 3-D features with 2-D features than using just 2-D features. This suggests that 3-D fingerprint features will be effective in the matching and the decision-making component of the internal fingerprint-based identification system.

With human observers used as a gold standard, mixture of Gaussians performed best in segmenting the 3-D papillary contour—internal fingerprint—according to the Hausdorff distance. On the selected pre-processing technique, the regularized anisotropic diffusion filter, the average Hausdorff distance was the lowest. The standard deviation was the lowest, which suggests that the mixture of Gaussians stably produces contours consistent with those of human volunteers. The average Hausdorff distance of the method is higher than that among human volunteers as the method does not outperform humans. To train novelty detection techniques that are compared, they were set at the same percentage error that they can make on the target data.

Other novelty detection routines can be used in the proposed segmentation workflow. There is little difference in the segmentation performance between the routines that were tested. We have not implemented 3-D internal fingerprint recognition routines to assess the impact of the difference in segmentation performance on the eventual recognition performance of the entire system. The impact of segmentation performance of different novelty detection routines on the overall system recognition performance might not be significant, in which case the novelty detection routines could be ranked by other desirable aspects, for instance speed.

Novelty detection techniques had the poorest performance segmenting OCT scans preprocessed with the total variation denoising filter, according to the Hausdorff distance. Such filtered cross-sectional images had high- and low-intensity specks across the epidermal and papillary layers observed visually. The specks negatively affected the performance of novelty detection routines. The kNN routine, which computes the distance to the optimized k nearest neighbours, had the best performance of these routines. Scans pre-processed with the anisotropic diffusion filter also had such specks, be it on a level less than that observed with the total variation denoising filter. That might explain why superior performance was obtained when using its regularized version. Quantitative performance evaluation of different filtering techniques was not explicitly done, and if done it will definitely order the different OCT speckle noise reduction techniques according to performance.

When the upper limit of the MWI confidence interval is greater than one, it demonstrates that an automatically detected contour agrees with the set of manual contours at least as well as manual segmentations are in agreement. The upper limit obtained with the best segmentation pipeline—using a regularized anisotropic diffusion filter and a mixture of Gaussians routine was not greater that one. To improve novelty detection, texture features could be explored. The epidermis and the dermis layers have different textures. Moreover, neighbourhood information was not incorporated in novelty detection as individual pixel values were used as features. A nine-pixel neighbourhood can be used as a feature set instead of a single pixel. This might better represent spatial information. Even though the computer-observer agreement was not at least as well as observer-observer agreement, the confidence interval was narrow suggesting that the variability was not erratic and that the method is stable.

Unrolling algorithms can be used to convert the segmented 3-D internal fingerprints to their 2-D equivalent fingerprints. The 2-D equivalent fingerprints will not have the distortions caused by pressure exerted when capturing conventional 2-D fingerprints. Alternatively, 3-D profile features can be extracted from the segmented 3-D internal fingerprints. Such features can be used for matching instead of features extracted from traditional contact-based scanners that often suffer non-linear distortions.

### 5. Conclusion

systems as physical deterioration of an external fingerprint will be countered by using the

Sousedik et al. [12] used a support vector machine to detect the layer that corresponds to a fake fingerprint glued to a fingertip, using the overall energy of the layers as a feature vector. They did not use machine learning for matching different fingertips but rather for detecting artefacts glued to fingertips. Kumar and Kwong [25] implemented matching the 3-D surface fingerprints obtained using a single camera, using both the finger surface code and 3-D minutiae as features. They got a better matching performance when combining 3-D features with 2-D features than using just 2-D features. This suggests that 3-D fingerprint features will be effective in the matching and the decision-making component of the internal fingerprint-based

With human observers used as a gold standard, mixture of Gaussians performed best in segmenting the 3-D papillary contour—internal fingerprint—according to the Hausdorff distance. On the selected pre-processing technique, the regularized anisotropic diffusion filter, the average Hausdorff distance was the lowest. The standard deviation was the lowest, which suggests that the mixture of Gaussians stably produces contours consistent with those of human volunteers. The average Hausdorff distance of the method is higher than that among human volunteers as the method does not outperform humans. To train novelty detection techniques that are compared, they were set at the same percentage error that they can make

Other novelty detection routines can be used in the proposed segmentation workflow. There is little difference in the segmentation performance between the routines that were tested. We have not implemented 3-D internal fingerprint recognition routines to assess the impact of the difference in segmentation performance on the eventual recognition performance of the entire system. The impact of segmentation performance of different novelty detection routines on the overall system recognition performance might not be significant, in which case the novelty

Novelty detection techniques had the poorest performance segmenting OCT scans preprocessed with the total variation denoising filter, according to the Hausdorff distance. Such filtered cross-sectional images had high- and low-intensity specks across the epidermal and papillary layers observed visually. The specks negatively affected the performance of novelty detection routines. The kNN routine, which computes the distance to the optimized k nearest neighbours, had the best performance of these routines. Scans pre-processed with the anisotropic diffusion filter also had such specks, be it on a level less than that observed with the total variation denoising filter. That might explain why superior performance was obtained when using its regularized version. Quantitative performance evaluation of different filtering techniques was not explicitly done, and if done it will definitely order the different OCT speckle

When the upper limit of the MWI confidence interval is greater than one, it demonstrates that an automatically detected contour agrees with the set of manual contours at least as well as manual segmentations are in agreement. The upper limit obtained with the best segmentation

detection routines could be ranked by other desirable aspects, for instance speed.

noise reduction techniques according to performance.

internal fingerprint.

202 Computed Tomography - Advanced Applications

identification system.

on the target data.

The proposed workflow automatically segments the contours of the papillary layer—the internal fingerprint. The 3-D OCT scan is processed on a per cross-sectional image basis. First, the slices are filtered by a regularized anisotropic diffusion filter to reduce the effects of speckle noise. Then, the Otsu method is used to detect the stratum corneum, and multilevel image thresholds are determined automatically for each slice. The stratum corneum is used as a marker to extract a set of epidermal layer pixels to be used as the training data in the ensuing novelty detection. The mixture of Gaussians mapping is used to label pixels at a depth higher than the depth used to extract the training pixels on each cross section. The contour of the papillary layer is the internal fingerprint. The 3-D internal fingerprint image is obtained by concatenating the 2-D papillary contours together.

Laser radiation loses focus towards the extremes of a fingertip because of the fingertip's curvature. The result is that skin penetration weakens and the weak reflected light translates into low-pixel intensity values. This affects stratum corneum detection, and at times, the Otsu segmentation method returns a non-continuous stratum corneum edge. Corneum stratum edge detection will be improved using regression methods. The left topmost and right topmost extreme pixels of the returned connected components constituting the stratum corneum can be stitched together. Vertically sweeping an image from left to right, the right topmost extreme point will be connected to the closest, Euclidean distance-wise, left topmost extreme pixel using regression methods. A linear least squares fitting technique will not always give the output as a single connected object when fed with two disjointed edges in an image; hence, non-linear regression routines will be investigated.

The epidermis extends to an average of 0.34 mm at the finger region [8]. The 10-pixels depth from which the extraction of the epidermis layer began was empirically determined. The aim was to exclude the stratum corneum was extracting pixels that forms the training set of novelty detection routines. The routines were given pixel values at a depth higher than the extracted training pixel dataset to classify, with the undulations of the papillary contour expected to be the border between the target and rejection regions.

An automated segmentation workflow has been established for the 3-D internal fingerprint. The segmented internal fingerprint does not suffer problems associated with the external fingerprint. The method preserves the 3-D profile features that are lost with the 2-D fingerprints' pattern. It has the potential to segment the papillary contours as well as a manual segmentation, with post-processing improvements.

### Author details

Rethabile Khutlang<sup>1</sup> \*, Pheeha Machaka<sup>2</sup> , Ann Singh<sup>3</sup> and Fulufhelo Nelwamondo<sup>4</sup>

\*Address all correspondence to: rkhutlang@csir.co.za

1 Biometrics Research Group, Identity Authentication, CSIR Modelling and Digital Science, Pretoria, South Africa

2 Network Security, Network and Data Security, CSIR Modelling and Digital Science, Pretoria, South Africa

3 Laser Sources Group, CSIR National Laser Centre, Pretoria, South Africa

4 CSIR Modelling and Digital Science, Pretoria, South Africa

### References


[6] Manapuram, R. K., Ghosn, M., Larin, K. V.: Identification of artificial fingerprints using optical coherence tomography technique. Asian Journal of Physics, 2006; 15: 15–27

detection routines. The routines were given pixel values at a depth higher than the extracted training pixel dataset to classify, with the undulations of the papillary contour expected to be

An automated segmentation workflow has been established for the 3-D internal fingerprint. The segmented internal fingerprint does not suffer problems associated with the external fingerprint. The method preserves the 3-D profile features that are lost with the 2-D fingerprints' pattern. It has the potential to segment the papillary contours as well as a manual

1 Biometrics Research Group, Identity Authentication, CSIR Modelling and Digital Science,

2 Network Security, Network and Data Security, CSIR Modelling and Digital Science, Pretoria,

[1] Jain, A., Ross, A., Prabhakar, S.: An introduction to biometric recognition. IEEE Trans-

[2] Shiratsuki, A., Sano, E., Shikai, M., et al.: Novel optical fingerprint sensor utilizing optical characteristics of skin tissue under fingerprints. Biomedical Optics, International Society

[3] Maltoni, D., Cappelli, R.: Advances in fingerprint modeling. Image and Vision Comput-

[4] Cheng, Y., Larin, K. V.: In vivo two-and three-dimensional imaging of artificial and real fingerprints with optical coherence tomography. IEEE Photonics Technology Letters,

[5] Kücken, M., Newell, A. C.: A model for fingerprint formation. EPL (Europhysics Letters),

actions on Circuits and Systems for Video Technology, 2004; 14(1): 4–20

3 Laser Sources Group, CSIR National Laser Centre, Pretoria, South Africa

, Ann Singh<sup>3</sup> and Fulufhelo Nelwamondo<sup>4</sup>

the border between the target and rejection regions.

204 Computed Tomography - Advanced Applications

segmentation, with post-processing improvements.

\*, Pheeha Machaka<sup>2</sup>

4 CSIR Modelling and Digital Science, Pretoria, South Africa

for Optics and Photonics, 2005; 80–87

ing, 2009; 27(3): 258–268

2007; 19(20): 1634–1636

2004; 68(1): 141

\*Address all correspondence to: rkhutlang@csir.co.za

Author details

Rethabile Khutlang<sup>1</sup>

Pretoria, South Africa

South Africa

References


## **The Use of Computed Tomography to Explore the Microstructure of Materials in Civil Engineering: From Rocks to Concrete**

Miguel A. Vicente, Jesús Mínguez and Dorys C. González

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69245

#### **Abstract**

[23] Chalana, V., Kim, Y.: A methodology for evaluation of boundary detection algorithms on medical images. IEEE Transactions on Medical Imaging, 1997; 16(5): 642–652

[24] Khutlang, R., Nelwamondo, F. V.: Novelty detection-based internal fingerprint segmentation in optical coherence tomography images. In 2014 Second International Symposium on Computing and Networking (CANDAR), Shizuoka, December 2014, pp. 556–559 [25] Kumar, A., Kwong, C.: Towards contactless, low-cost and accurate 3D fingerprint identification. IEEE Transactions on Pattern Analysis and Machine Intelligence, 2015; 37(3):

681–696

206 Computed Tomography - Advanced Applications

Computed tomography (CT) is a nondestructive technique, based on absorbing X-rays, that permits the visualisation of the internal microstructure of material. The field of application is very wide. This is a well-known technology in medicine, because of its enormous advantages, but it is also very useful in other fields. Computed tomography is used in palaeontology to study the internal structure of the bones from ancient hominids. In addition, this technology is being used by engineers to analyse the microstructure of materials. Materials engineers use this technology to analyse or develop new materials. Mechanical engineers use CT scans to study the internal defects of materials. Geotechnical engineers use CT scans to study several aspects of the rocks and minerals (cracks, voids, etc). This technology is also very useful to study de microstructure of concrete, especially in case of the new concretes (ultra-high performance concrete, fiber reinforced concrete, etc). In this chapter, an extended state-of-the-art of the most relevant research, related to the use of computed tomography to explore the microstructure of materials in civil and mechanical engineering, is exposed. The main objective of this chapter is that the reader can discover new applications of the computed tomography, different from conventional ones.

**Keywords:** CT scan, rocks, high performance concrete, fiber-reinforced high performance concrete

### **1. Introduction to computed tomography (CT) scan technology**

Ever since Wilhelm Röntgen discovered X-rays in 1895, these rays have been used in many scientific fields. One property of this type of radiation is that it can travel through matter, losing

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

energy on the way, in accordance with the law of Beer that equates intensity I with a monochromatic X-ray travelling through an object in terms of the following expression (Eq. (1)).

$$I = I\_0 \cdot \exp\{-\mathfrak{f}\,\mu(\mathbf{s})ds\} \tag{1}$$

where *I* 0 is the initial intensity of the ray and *μ*(*s*) the linear attenuation coefficient along its trajectory.

The aforementioned linear attenuation coefficient, μ, fundamentally depends on the density, ρ, of the material at each point through which the ray travels. The quotient μ/ρ is approximately proportional to Z3 in the standard range used in the computed tomography (CT) scans, where Z is the atomic number of the element.

CT is a nondestructive technique used to analyze the internal microstructure of materials based on the above-mentioned property of X-rays. The tomography equipment is composed of an emitter, which emits a ray at a given intensity, and a detector, which registers the reception intensity of the ray. In the analysis, the object revolves in front of the apparatus, consisting of the emitter, emitting rays in all directions on the plane, and the detector. Postprocessing of the signal to produce attenuation-corrected images, which coincide with the measurement of attenuation, means that the density of each point of the specimen under study may be determined. This process is repeated for different sections of the specimen, thereby obtaining tri-dimensional (tomographic) information. Alternatively, a conic beam of X-rays can be emitted that are collected on a flat detector. In this case, only the specimen has to revolve, and relative displacement between the emitter-detector apparatus and the specimen is unnecessary (**Figure 1**):

In all cases, the practical result is a tri-dimensional image, in grey scale, in which each grey area corresponds to a particular density value. Clearer tones represent higher densities, and darker tones represent lower densities.

The use of this technique commenced in medicine, during the last century, around the 1970s, as a non-invasive technique to explore the internal parts of patients, to display the inside of the body (organs, tissue, bones, etc.) and to detect abnormal structures that can indicate some pathology.

Over recent years, the technique has been discarded in medicine; however, it has been used in a more intense way in other scientific fields, especially science and engineering, where all variants of computerized tomography are increasingly employed.

In the 1980s, high-resolution tomographic equipment emerged commonly called micro CT scan. This new equipment used new sources of emissions, in the form of gamma rays and synchrotron radiation. At present, synchrotron radiation is the most widely used in modern equipment because of its high resolution and sharpness.

There are substantial differences between a CT scan for medical purposes and a CT scan in research and in the industrial sector. In the former case concerning medical equipment, the specimen or patient remains immobile, and it is the emitter-receptor apparatus that moves and revolves. However, it is the specimen that is moved and turned in an industrial or research CT scan.

Moreover, the equipment used in medicine presents very low intensity values because of the effects of high radiation on human health. These levels of radiation result in lower resolution and sharpness (**Figures 2** and **3**):

The Use of Computed Tomography to Explore the Microstructure of Materials in Civil Engineering... http://dx.doi.org/10.5772/intechopen.69245 209

**Figure 1.** The principle of the working of a CT scan [1].

energy on the way, in accordance with the law of Beer that equates intensity I with a monochromatic X-ray travelling through an object in terms of the following expression (Eq. (1)).

The aforementioned linear attenuation coefficient, μ, fundamentally depends on the density, ρ, of the material at each point through which the ray travels. The quotient μ/ρ is approx-

CT is a nondestructive technique used to analyze the internal microstructure of materials based on the above-mentioned property of X-rays. The tomography equipment is composed of an emitter, which emits a ray at a given intensity, and a detector, which registers the reception intensity of the ray. In the analysis, the object revolves in front of the apparatus, consisting of the emitter, emitting rays in all directions on the plane, and the detector. Postprocessing of the signal to produce attenuation-corrected images, which coincide with the measurement of attenuation, means that the density of each point of the specimen under study may be determined. This process is repeated for different sections of the specimen, thereby obtaining tri-dimensional (tomographic) information. Alternatively, a conic beam of X-rays can be emitted that are collected on a flat detector. In this case, only the specimen has to revolve, and relative displacement between the emitter-detector apparatus and the specimen is unnecessary (**Figure 1**):

In all cases, the practical result is a tri-dimensional image, in grey scale, in which each grey area corresponds to a particular density value. Clearer tones represent higher densities, and

The use of this technique commenced in medicine, during the last century, around the 1970s, as a non-invasive technique to explore the internal parts of patients, to display the inside of the body (organs, tissue, bones, etc.) and to detect abnormal structures that can indicate some pathology. Over recent years, the technique has been discarded in medicine; however, it has been used in a more intense way in other scientific fields, especially science and engineering, where all

In the 1980s, high-resolution tomographic equipment emerged commonly called micro CT scan. This new equipment used new sources of emissions, in the form of gamma rays and synchrotron radiation. At present, synchrotron radiation is the most widely used in modern

There are substantial differences between a CT scan for medical purposes and a CT scan in research and in the industrial sector. In the former case concerning medical equipment, the specimen or patient remains immobile, and it is the emitter-receptor apparatus that moves and revolves. However, it is the specimen that is moved and turned in an industrial or research CT scan.

Moreover, the equipment used in medicine presents very low intensity values because of the effects of high radiation on human health. These levels of radiation result in lower resolution

variants of computerized tomography are increasingly employed.

equipment because of its high resolution and sharpness.

is the initial intensity of the ray and *μ*(*s*) the linear attenuation coefficient along its

· *exp*{− ∫ *μ*(*s*)*ds*} (1)

in the standard range used in the computed tomography (CT)

0

*I* = *I*

208 Computed Tomography - Advanced Applications

darker tones represent lower densities.

and sharpness (**Figures 2** and **3**):

scans, where Z is the atomic number of the element.

imately proportional to Z3

where *I* 0

trajectory.

**Figure 2.** An example of medical CT scan. Courtesy of Siemens.

**Figure 3.** An example of medical CT scan. Courtesy of YXLON.

### **2. Use of CT scan technology in paleontology**

Paleontology is one of the first scientific fields in which the use of computerized tomography started outside of medicine. Obviously, the technique of analyzing the bones of hominids and dinosaurs hardly differs from the technique used with humans and animals that are alive.

Numerous research papers have published studies in this field in which the CT scan is a very valuable instrument.

The fossilization process of an organism takes place over thousands of years, during which time loss and fragmentation of bones and other hard parts of the skeleton, decomposition, and so on occur. In addition, breakage occurs during their manipulation and study, which can imply an enormous loss. The primary objective of paleontological investigation is the reconstruction of skeletons and, from that point, to interpret many other biological and environmental characteristics, and so on.

The CT scan is a very useful tool here because it permits exact tridimensional images and, by means of software for the post-processing of images, can reconstruct skeletons without any need to manipulate the pieces. In addition, the information collected by the CT scan can serve as the basis for the regeneration of exact replicas using 3D printers [2–6].

In other cases, it may be physically impossible to remove the rocky sediment that hardens around the fossil. In that case, the CT scan can virtually eliminate it, revealing the "clean" piece [7] (**Figure 4**):

**Figure 4.** Virtual reconstruction and cleaning [7].

In other cases, the CT scan can determine the biomechanical parameters of the fossils [8] and detect disease and pathologies [9].

Recently, some research works have been published, in which possible alterations to the sample, due to the radiation emitted by the CT-Scan in the course of dating studies, are analyzed [10, 11].

### **3. Use of CT scan technology in heritage and ancient relics**

**2. Use of CT scan technology in paleontology**

valuable instrument.

210 Computed Tomography - Advanced Applications

**Figure 4.** Virtual reconstruction and cleaning [7].

Paleontology is one of the first scientific fields in which the use of computerized tomography started outside of medicine. Obviously, the technique of analyzing the bones of hominids and dinosaurs hardly differs from the technique used with humans and animals that are alive. Numerous research papers have published studies in this field in which the CT scan is a very

The fossilization process of an organism takes place over thousands of years, during which time loss and fragmentation of bones and other hard parts of the skeleton, decomposition, and so on occur. In addition, breakage occurs during their manipulation and study, which can imply an enormous loss. The primary objective of paleontological investigation is the reconstruction of skeletons and, from that point, to interpret many other biological and environmental characteristics, and so on. The CT scan is a very useful tool here because it permits exact tridimensional images and, by means of software for the post-processing of images, can reconstruct skeletons without any need to manipulate the pieces. In addition, the information collected by the CT scan can serve

In other cases, it may be physically impossible to remove the rocky sediment that hardens around the fossil. In that case, the CT scan can virtually eliminate it, revealing the "clean" piece [7] (**Figure 4**):

as the basis for the regeneration of exact replicas using 3D printers [2–6].

Relics and ancient artifacts, to some extent, share the characteristics of fossils, explained in the earlier section. In the first place, these objects are of singular value, so they have to be handled with great care. In many cases, they are pieces that have remained buried for thousands of years and may be covered by layers of rocky sediment that is strongly attached, the mechanical removal of which implies a serious problem for the piece.

In these cases, the use of CT scan technology is of enormous interest. In the first place, the archaeological piece may be separated from the surrounding sediment as a virtual replica. In this way, the piece may be examined with the naked eye and studied without damaging it. Moreover, on the basis of the information obtained by the CT scan, exact replicas of the piece may be produced, using 3D printers. This option allows researchers to manipulate the replicas and to study them without the dangers, and the limitations involved in handling the original piece. It is also of interest for museums, as they can exhibit the replicas, for keeping the original piece safe in storage [12–16]. (**Figure 5**).

In other cases, the pieces are extremely delicate, such as paintings [17] and mummies [18]. In both cases, an analysis by means of CT scan technology preserves the integrity of the piece.

**Figure 5.** An example of rendering a prayer nut [12].

### **4. Use of CT scan technology in asphalt mixtures**

Asphalt mixtures are widely used in the construction of road pavements and airports, because of the advantages that they contribute, among which are high strength, easy manufacturing and maintenance, low noise emission, and so on.

From the structural point of view, asphalt mixtures are heterogeneous materials, composed of aggregates, asphalt, and porous networks. Their mechanical properties show high levels of dispersion, given that those properties depend on many factors, such as the form and the distribution of the aggregate, the asphalt content, the pore content, pore distribution, and so on.

Comparative numeric models, as close as possible to the real specimens, need to be developed, in order to understand the behavior of the asphalt mixtures better. In this sense, the CT scan is of great assistance, as it generates the exact geometry of the internal structure of the asphaltic mixture and subsequently a finite elements model (FEM) with which the real capacity may be estimated against certain external actions. Comparing the numerical results with the tests carried out on the real specimen, it is possible to advance in the calibration of these models that predict the behavior of the material to improve its properties [19–23] (**Figure 6**).

In the case of special asphalts, it may be of great interest to know the exact distribution of certain compounds, with a view to understand their effectiveness. This situation applies to both additives for pavement restoration [24] and fiber-reinforced asphalts [24]. In many cases, with the assistance of the CT scan, correlations are sought between the mechanical behavior of the asphalt mix and its internal microstructure [25–28].

**Figure 6.** Extraction of the area of interest using CT scan technology [19].

### **5. Use of CT scan technology in rock mineralogy**

**4. Use of CT scan technology in asphalt mixtures**

and maintenance, low noise emission, and so on.

212 Computed Tomography - Advanced Applications

asphalt mix and its internal microstructure [25–28].

**Figure 6.** Extraction of the area of interest using CT scan technology [19].

Asphalt mixtures are widely used in the construction of road pavements and airports, because of the advantages that they contribute, among which are high strength, easy manufacturing

From the structural point of view, asphalt mixtures are heterogeneous materials, composed of aggregates, asphalt, and porous networks. Their mechanical properties show high levels of dispersion, given that those properties depend on many factors, such as the form and the distribution of the aggregate, the asphalt content, the pore content, pore distribution, and so on.

Comparative numeric models, as close as possible to the real specimens, need to be developed, in order to understand the behavior of the asphalt mixtures better. In this sense, the CT scan is of great assistance, as it generates the exact geometry of the internal structure of the asphaltic mixture and subsequently a finite elements model (FEM) with which the real capacity may be estimated against certain external actions. Comparing the numerical results with the tests carried out on the real specimen, it is possible to advance in the calibration of these models that predict the behavior of the material to improve its properties [19–23] (**Figure 6**).

In the case of special asphalts, it may be of great interest to know the exact distribution of certain compounds, with a view to understand their effectiveness. This situation applies to both additives for pavement restoration [24] and fiber-reinforced asphalts [24]. In many cases, with the assistance of the CT scan, correlations are sought between the mechanical behavior of the Since the 1980s, research has taken place in which CT scan technology has been applied to the analysis of the internal microstructures of rocks.

Rocks are heterogeneous materials containing pores and fissures and consisting of various materials, with different mechanical properties and of varying density. On many occasions, the structural behavior of a rock is strongly conditioned by its microstructure, especially in reference to pores and fissures.

Rock, as a structural material, is present in a range of civil engineering works, among which tunnels and dams are prominent. In tunnels, the mechanical characteristics of the rocks, their porosity, and their degree of internal fracturing strongly condition their stability, their convergence, and so on.

Something similar occurs in the case of dams, especially arch dams. These structural elements are cemented to rock faces, and their structural safety is strongly dependent on the mechanical behavior of the rocks. The existence of failure planes or excessive internal fissuring might mean that the dam is not stable against the loads that it transfers, or it is not sufficiently watertight to ensure the retention of the water in the reservoir.

The foundations of large bridges, generally very deep foundations constructed with piles, usually reach down to the bedrock. Once again, the geological and mechanical characteristics of the rock clearly determine the structural safety of the bridge.

The possibilities offered by CT scanning in the field of geo-mineralogy are enormous [1, 29– 31]. In all of these cases, CT scan technology has been successfully used to understand the microstructure of the bedrock and its behavior in reaction to certain physical and mechanical processes (**Figure 7**).

**Figure 7.** Example of the possibilities of CT scan technology in rocks [29]. This time, the sequence shows a pore filling event.

Porosity, linked to water absorption capacity, is a very important parameter in rocks, as demonstrated by the high number of scientific publications in this field. At present, the most relevant investigations are currently applying CT scan technology to evaluate porosity, regardless of whether it has structural consequences [32, 33]. Other investigative works have analyzed mechanical behavior and its connection with the mineralogical microstructure [34].

One of the variants of this theme is the study of petrous elements for their use in construction. A theme of great interest is the study of porosity in limestone used, for example, in façades and pedestrian pavements, as well as for the rehabilitation of historic buildings and as a masonry element. In all of these cases, determination of the porosity of limestone is essential when determining whether it is convenient for use in a particular climate. In the case of environments subjected to freezing-thawing cycles, a high porosity substantially reduces the working life of the limestone.

On this point, it is worth highlighting the studies developed by Dewanckele et al. [35] and Boone et al. [36], in which the behavior of porous limestone was analyzed against erosive processes and water absorption. To do so, CT scanning was used to analyze how the internal structure of the limestone evolves due to the aforementioned processes (**Figure 8**).

**Figure 8.** The example of rendering volumes of the changing pores in limestone [35]. The pores are color coded from red (large) to blue (small). Drawing A belongs to unweathered state, drawing B belongs to 6 days of weathering process, and drawing C belongs to 21 days of weathering process.

### **6. Use of CT scan technology in metals**

Porosity, linked to water absorption capacity, is a very important parameter in rocks, as demonstrated by the high number of scientific publications in this field. At present, the most relevant investigations are currently applying CT scan technology to evaluate porosity, regardless of whether it has structural consequences [32, 33]. Other investigative works have analyzed mechanical behavior and its connection with the mineralogical

One of the variants of this theme is the study of petrous elements for their use in construction. A theme of great interest is the study of porosity in limestone used, for example, in façades and pedestrian pavements, as well as for the rehabilitation of historic buildings and as a masonry element. In all of these cases, determination of the porosity of limestone is essential when determining whether it is convenient for use in a particular climate. In the case of environments subjected to freezing-thawing cycles, a high porosity substantially reduces the

On this point, it is worth highlighting the studies developed by Dewanckele et al. [35] and Boone et al. [36], in which the behavior of porous limestone was analyzed against erosive processes and water absorption. To do so, CT scanning was used to analyze how the internal

**Figure 8.** The example of rendering volumes of the changing pores in limestone [35]. The pores are color coded from red (large) to blue (small). Drawing A belongs to unweathered state, drawing B belongs to 6 days of weathering process, and

structure of the limestone evolves due to the aforementioned processes (**Figure 8**).

microstructure [34].

214 Computed Tomography - Advanced Applications

working life of the limestone.

drawing C belongs to 21 days of weathering process.

Metals are widely used materials in the industrial sector. At present, innumerable types of simple metals and alloys are used, each one of them with specific properties, useful for the function that they have to perform: very light or carrying heavy loads, electrical conductivity or otherwise, high and low thermal transmissivity, tenacity and fracture strength, abrasion resistance, hardness, mechanical capacity, corrosion resistance, and so on.

Metals are used in all fields of industrial engineering, without exception. Metal manufacturing processes are very varied, ranging from smelting and casting to more modern systems of stamping and injection. In general, the metals used in different fields present optimal properties for the function they will serve, with the optimal design of parts in terms of material consumption.

The use of CT scan technology is quite widespread in the industrial sector, especially in those sectors that develop elements of high added value (aeronautical, aerospatial, automotive sectors, etc). One very common line of investigation, in which CT scan technology plays a relevant role, is the study of defects produced during the manufacturing process, with a view to their improvement [37–40]. In some cases, comparisons have been established between the microstructure of the material and its mechanical behavior [41–44]. In these cases, the information obtained by means of CT scanning is used for the generation of the tridimensional FEM models for the numerical simulation of the expected results and their subsequent comparison with the values measured in the tests. Here, the advantage of CT scanning is that it permits the construction of exact numerical models, which not only includes the different phases that constitute the piece but also the pores, defects, fissures, and so on in their exact position (**Figure 9**).

Within this line of investigation, it is worth highlighting welded joints and their analysis [45]. Welding is the most extensive process, whenever possible, for joining together two metallic parts. The way in which the welding is done is fundamental to the final quality of the joint.

**Figure 9.** The example of an analysis of mechanical behavior of metal under compression and CT scan analysis [44]. (a) Sequential deformation recorded with a video camera and (b) sequential deformation "recorded" with a CT scan.

In this sense, as in the earlier case, the defects produced in the weld can be evaluated during welding with CT scan technology helping to improve the process.

One particular case of metals, used from a structural point of view, is composite metals, generally composed of a bland or foamy metallic matrix to which fibers or particles are usually added to improve their rigidity and strength [46]. In these cases, the microstructure of the composite material may be analyzed with CT scan technology, evaluating the distribution of the reinforcement, its orientation in the case of fibers, and so on.

### **7. Use of CT scan technology in composites**

Composite materials are widely used in engineering. They are generally composed of a matrix and reinforcement that is generally of particles or fibers. The reinforcement has the role of modifying the natural properties of the matrix, with the objective of achieving a material of the desired characteristics.

In general, in a composite material, three phases may be distinguished: matrix, reinforcement, and pores or cracks.

The behavior of the composite materials strongly depends on the distribution and the orientation of the reinforcement (the latter solely in the case of fibers) as well as the location in the pores and cracks.

Of great interest in this field, CT scan technology permits the evaluation of the microstructure of the composite material [47–52]. In many cases, the combined use of CT scan and mechanical or thermal characterization tests of the composite material allows relations to be established between the microstructure and its macroscopic response [53–57] (**Figure 10**).

**Figure 10.** The example of analysis of the microstructure of a composite [47]. (a) 3D braid geometry, (b) 3D braid geometry with imperfections, (c) 3D distribution imperfections, and (d) detailed view.

As commented in earlier sections, a CT scan is the basis for the generation of exact FEM models, from which numerical simulations of all kinds may be performed [58, 59].

### **8. Use of CT scan technology in concrete**

In this sense, as in the earlier case, the defects produced in the weld can be evaluated during

One particular case of metals, used from a structural point of view, is composite metals, generally composed of a bland or foamy metallic matrix to which fibers or particles are usually added to improve their rigidity and strength [46]. In these cases, the microstructure of the composite material may be analyzed with CT scan technology, evaluating the distribution of

Composite materials are widely used in engineering. They are generally composed of a matrix and reinforcement that is generally of particles or fibers. The reinforcement has the role of modifying the natural properties of the matrix, with the objective of achieving a material of

In general, in a composite material, three phases may be distinguished: matrix, reinforcement,

The behavior of the composite materials strongly depends on the distribution and the orientation of the reinforcement (the latter solely in the case of fibers) as well as the location in the

Of great interest in this field, CT scan technology permits the evaluation of the microstructure of the composite material [47–52]. In many cases, the combined use of CT scan and mechanical or thermal characterization tests of the composite material allows relations to be established between the microstructure and its macroscopic response [53–57] (**Figure 10**).

**Figure 10.** The example of analysis of the microstructure of a composite [47]. (a) 3D braid geometry, (b) 3D braid geometry

with imperfections, (c) 3D distribution imperfections, and (d) detailed view.

welding with CT scan technology helping to improve the process.

the reinforcement, its orientation in the case of fibers, and so on.

**7. Use of CT scan technology in composites**

the desired characteristics.

216 Computed Tomography - Advanced Applications

and pores or cracks.

pores and cracks.

Concrete is one of the most widely used materials in the construction of infrastructure and buildings. One of the reasons for its extensive use is the relatively low price of extracting petrous materials from the environment. Another reason is the possibility of molding its geometry as it is poured in the fresh (fluid) state. The composition of concrete is highly heterogeneous as its matrix is composed of different materials: cement, sand, and rough aggregate. The dosages of those elements are modified to obtain optimum mechanical capacities. Additionally, other types of materials are used to improve the performance of the concrete such as fibers and additives to modify the internal structure of the material.

Internally, what is generated is a matrix composed of aggregate fines and hydrated cement that cover the coarse aggregate (**Figure 11**).

It is noteworthy that there are a multitude of parameters with a role in the final characteristic. The dosages of the different components are based on experimentation due to the different typologies or aggregates, sand, and cement that are available on the market. As an example, if in one region, the rocky material in the surrounding environment is granite, the aggregate will be based on this material.

**Figure 11.** Polypropylene fiber-reinforced concrete specimen. Aggregates (in white), cement matrix (in soft grey), polypropylene fibers (in dark grey), and porous (in black) can be identified. Courtesy of the University of Burgos (Spain).

Moreover, concretes with additional qualities are under development in which fibers are added to their mixtures. There is at present a large quantity of fiber typologies in the market, so that at present, there is a broad process of investigation aimed at generating an optimal concrete in accordance with the desired performance.

Besides, public administrations are considering sustainability criteria that imply the development of research that aims to produce concrete that incorporates recycled materials, so as to reduce the carbon footprint and the environmental impact.

Therefore, in view of the above, it may be said that even though concrete is a priori a relatively rough and ready technology, constant development and improvements in performance, as well as new applications in construction elements are topics that are in the investigative projects of universities and research centers throughout the world.

New tools that provide the researcher with information to supplement the results of conventional tests have been incorporated to analyze concrete in this process of innovation for the determination of mechanical characteristics.

One of these tools that can be used to analyze the internal matrix of concretes and mortars is the computed tomography scan. The researcher is capable of analyzing unaltered samples of concrete in a non-destructive way, for example, in order to determine whether certain geometric patterns exist that can in turn classify the physical characteristics of the sample.

Next, some of the practical applications of computerized tomography to concretes are described.

### **8.1. Application to the analysis of the internal matrix**

Among the applications of the CT scan technology for the analysis of a concrete matrix, there are some experimental studies focused on recycled concretes [60]. In these studies, concretes with equal percentages of 50% recycled aggregate (RCA) and 50% natural aggregates were analyzed. The objective of the use of tomography is to evaluate the interfaces between both types of concretes. In addition, the porosity of each type of matrix is analyzed (**Figure 12**).

The identification of pores provides information on these internal gaps that the matrix presents. This information may relate to the size of the pores and their distribution within the specimen. Information may also be extracted on the sphericity of the pores that is compared with a perfect sphere and finally, the spatial position of these pores within the matrix [61] (**Figure 13**).

The application of superabsorbent polymers (SAP) for the development of high performance concretes with the aim of reducing hydration-related problems of the cementitious matrix generates variations in the distribution of the pores within the concrete matrix and its porosity. These changes lead to modifications in the physical properties of the component [62].

Images of the spatial distribution of the pores may be obtained by means of computerized topography image analysis and the use of post-processing tools including volumes, numbers of pores, positions within the specimen, and sphericity indexes.

In this way, researchers can determine how the porosity map of the specimen is modified for different types of SAP additions (**Figure 14**).

The Use of Computed Tomography to Explore the Microstructure of Materials in Civil Engineering... http://dx.doi.org/10.5772/intechopen.69245 219

**Figure 12.** Interface paste-aggregate and porosity between matrices with recycled aggregates and natural aggregates [60].

**Figure 13.** Identification and classification of pores in sizes [61].

Moreover, concretes with additional qualities are under development in which fibers are added to their mixtures. There is at present a large quantity of fiber typologies in the market, so that at present, there is a broad process of investigation aimed at generating an optimal

Besides, public administrations are considering sustainability criteria that imply the development of research that aims to produce concrete that incorporates recycled materials, so as to

Therefore, in view of the above, it may be said that even though concrete is a priori a relatively rough and ready technology, constant development and improvements in performance, as well as new applications in construction elements are topics that are in the investigative proj-

New tools that provide the researcher with information to supplement the results of conventional tests have been incorporated to analyze concrete in this process of innovation for the

One of these tools that can be used to analyze the internal matrix of concretes and mortars is the computed tomography scan. The researcher is capable of analyzing unaltered samples of concrete in a non-destructive way, for example, in order to determine whether certain geometric patterns exist that can in turn classify the physical characteristics of the sample.

Next, some of the practical applications of computerized tomography to concretes are described.

Among the applications of the CT scan technology for the analysis of a concrete matrix, there are some experimental studies focused on recycled concretes [60]. In these studies, concretes with equal percentages of 50% recycled aggregate (RCA) and 50% natural aggregates were analyzed. The objective of the use of tomography is to evaluate the interfaces between both types of concretes. In addition, the porosity of each type of matrix is analyzed (**Figure 12**). The identification of pores provides information on these internal gaps that the matrix presents. This information may relate to the size of the pores and their distribution within the specimen. Information may also be extracted on the sphericity of the pores that is compared with a perfect sphere and finally, the spatial position of these pores within the matrix [61] (**Figure 13**). The application of superabsorbent polymers (SAP) for the development of high performance concretes with the aim of reducing hydration-related problems of the cementitious matrix generates variations in the distribution of the pores within the concrete matrix and its porosity.

These changes lead to modifications in the physical properties of the component [62].

of pores, positions within the specimen, and sphericity indexes.

different types of SAP additions (**Figure 14**).

Images of the spatial distribution of the pores may be obtained by means of computerized topography image analysis and the use of post-processing tools including volumes, numbers

In this way, researchers can determine how the porosity map of the specimen is modified for

concrete in accordance with the desired performance.

218 Computed Tomography - Advanced Applications

reduce the carbon footprint and the environmental impact.

ects of universities and research centers throughout the world.

determination of mechanical characteristics.

**8.1. Application to the analysis of the internal matrix**

**Figure 14.** Identification of pores inside concrete matrix [62].

In addition to the pores, the distribution of polymeric components is established. In the following image, the way each of the components of the polymer is obtained following segmentation and their grouping is shown (**Figure 15**).

### **8.2. Applications to visualize fiber distribution**

The addition of fibers improves the characteristics of concretes used in many different applications. The clearest and most widely used application is for the improvement of mechanical performance. The fibers withstand traction forces that the concrete is incapable of withstanding. As with all petrous materials, concrete presents a very good capacity to withstand compressive forces, while its resistance to traction stress is relatively low.

Hence, the need to add strengthening elements, in the form of fibers to resist traction forces, is necessary.

By way of an example, fibers are in a phase of expansion in their application to self-compacting concretes. The distribution and quantity of fibers represent a fundamental role in the final stress-resistant capacities of the concrete element [63].

Another factor that influences the mechanical capacities of fiber-reinforced concretes is fiber orientation within the matrix in relation to the traction planes of the component.

**Figure 15.** Segmentation and packing of the concrete matrix [61].

There are different segmentation techniques for the determination of fiber orientation [64, 65] (**Figure 16**). In all cases, they begin with a common process divided into different phases:


Another application of computerized axial tomography consists of analyzing the way in which the fibers may be distinguished during the manufacturing process of pre-fabricated elements and how that affects the reinforcement bars in the element [66] (**Figures 17** and **18**).

**Figure 16.** Procedure to identify fibers. The courtesy of the University of Burgos (Spain).

In addition to the pores, the distribution of polymeric components is established. In the following image, the way each of the components of the polymer is obtained following segmen-

The addition of fibers improves the characteristics of concretes used in many different applications. The clearest and most widely used application is for the improvement of mechanical performance. The fibers withstand traction forces that the concrete is incapable of withstanding. As with all petrous materials, concrete presents a very good capacity to withstand compressive

Hence, the need to add strengthening elements, in the form of fibers to resist traction forces,

By way of an example, fibers are in a phase of expansion in their application to self-compacting concretes. The distribution and quantity of fibers represent a fundamental role in the final

Another factor that influences the mechanical capacities of fiber-reinforced concretes is fiber

orientation within the matrix in relation to the traction planes of the component.

tation and their grouping is shown (**Figure 15**).

**Figure 14.** Identification of pores inside concrete matrix [62].

220 Computed Tomography - Advanced Applications

**8.2. Applications to visualize fiber distribution**

is necessary.

forces, while its resistance to traction stress is relatively low.

stress-resistant capacities of the concrete element [63].

**Figure 15.** Segmentation and packing of the concrete matrix [61].

**Figure 17.** Fiber distribution around longitudinal rebars [66].

**Figure 18.** Schema of the fiber distribution and orientation during casting process [66].

### **8.3. Applications on internal analysis and cracking**

The technology of the CT scan allows researchers to conduct analyses of concrete at a macro-level to identify the damage that may be generated in its matrix due to physical and chemical factors.

As described in the above sections, three-dimensional maps may be generated with this tool, which help the researcher to understand the internal mechanics of the concrete. There is at present no other real alternative that can reach the sub-millimetric level of detail of which tomography is capable.

In the case of the practical application carried out by Kim, Yun, and Park [67], CT scan technology was used to analyze samples of concrete and mortar at high temperatures. The objective was to determine how variations in temperature affected the behavior of the internal pores of the material until their collapse. In the following image, the fissures that developed when the concrete was subjected to 1000°C are shown (**Figures 19** and **20**):

**Figure 19.** Fracture development at 1000°C [67].

The Use of Computed Tomography to Explore the Microstructure of Materials in Civil Engineering... http://dx.doi.org/10.5772/intechopen.69245 223

**Figure 20.** Imaging of fractures that developed at 1000°C [67].

**8.3. Applications on internal analysis and cracking**

222 Computed Tomography - Advanced Applications

**Figure 18.** Schema of the fiber distribution and orientation during casting process [66].

was subjected to 1000°C are shown (**Figures 19** and **20**):

**Figure 19.** Fracture development at 1000°C [67].

The technology of the CT scan allows researchers to conduct analyses of concrete at a macro-level to identify the damage that may be generated in its matrix due to physical and chemical factors. As described in the above sections, three-dimensional maps may be generated with this tool, which help the researcher to understand the internal mechanics of the concrete. There is at present no other real alternative that can reach the sub-millimetric level of detail of which tomography is capable.

In the case of the practical application carried out by Kim, Yun, and Park [67], CT scan technology was used to analyze samples of concrete and mortar at high temperatures. The objective was to determine how variations in temperature affected the behavior of the internal pores of the material until their collapse. In the following image, the fissures that developed when the concrete It was determined that the appearance of fissuring began at a temperature of 600°C, and that this damage fundamentally began to occur in the zones close to the edges of the specimen, in the external zones, progressing as the temperature increased towards critical values until it reached a point of collapse.

Other studies related to fracture mechanics have analyzed how the fissuring of an element evolves when subjected to a flexural-traction test by using scanned images, in order to create a finite element model and a model of discrete damage adjusted to the physical interactions detected in the images [68] (**Figure 21**).

Finally, the following paragraphs describe research work that has been developed to determine the damage produced under cyclic loading in concrete specimens. Different specimens subjected to fatigue cycles at stress levels of 60, 70, 80, and 90% of resistance to static compression were analyzed.

The specimens were introduced before and after subjecting them to fatigue in the CT scan AC. The fissures within the concrete and their development were compared. A 3DMA algorithm was used to calculate the "burn number" of the pores and fissures, a number that represents the distance of the voxels under analysis to the external surface of the pore. So, for example, the external voxels are assigned a value equal to zero. As the scan progresses into the interior of the pore or fissure, a higher value than the burn number is obtained [69]. Those voxels, in general within the value of 1, represented fissures of 1 voxel in width (**Figure 22**).

**Figure 21.** Results of three studies: real (left), using CT-Scan (middle), and FEM (right) [68].

**Figure 22.** Spatial representation of damage (burn number) to different stress levels [69].

Following the tests, a growth in the internal damage was observed as the stress levels of the uniaxial cyclic loading increased.

### **9. Conclusions**

CT scan technology is a powerful research tool, with wide use capabilities in many scientific fields, and not only in medicine.

In this chapter, a general review has been carried out by different fields of science and engineering in which CT scan technology is currently being used successfully. As can be seen, the possibilities of this technology are very large and allow relevant advances in the knowledge of the materials.

In the future, new equipment will be more powerful and more precise, which will allow us to see better the internal microstructure of our materials, which will help us to know them better and improve them, obtaining solutions adapted to each need.

### **Author details**

Miguel A. Vicente\*, Jesús Mínguez and Dorys C. González

\*Address all correspondence to: mvicente@ubu.es

Department of Civil Engineering, University of Burgos, Spain

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Following the tests, a growth in the internal damage was observed as the stress levels of the

**Figure 22.** Spatial representation of damage (burn number) to different stress levels [69].

CT scan technology is a powerful research tool, with wide use capabilities in many scientific

In this chapter, a general review has been carried out by different fields of science and engineering in which CT scan technology is currently being used successfully. As can be seen, the possibilities of this technology are very large and allow relevant advances in the knowledge of the materials.

uniaxial cyclic loading increased.

224 Computed Tomography - Advanced Applications

fields, and not only in medicine.

**9. Conclusions**


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Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69415

Wenzheng Yue and Yong Wang

#### Abstract

In this chapter, three-dimensional digital rock models can be constructed by the micron X-ray computed tomography (CT). Then, lattice gas automata was applied to simulate the flow of electrical current in the saturated digital rocks to reveal the non-Archie relation of resistivity index and water saturation (I-Sw). The flow of single-phase Newtonian fluid in pore space had been studied with LBM for calculating the absolute permeability. Moreover, we have developed a model based on digital rock to simulate thermal neutrons transporting for imaging the anisotropy of pore structure. The advantages of the model over traditional methods indicate that it can simultaneously consider both the separation of matrix and pore and the distribution of mineral components. The results of numerical simulation with Monte Carlo are in good agreement with the pore distribution from X-ray CT, which can further verify the validity of the new model. In contrast to the conventional conclusion, we find that the porosity calculated with neutron data can be affected by the anisotropy. Therefore, a new formula to relate the resolution of array detectors to the quality of imaging, had been proposed to analyze the critical resolution and to optimize the number of neutrons in each simulation.

Keywords: digital rock, numerical simulation, X-ray computed tomography, Monte Carlo method

### 1. Introduction

Due to extremely sensitive to the hydrogen [1, 2], neutron radiography (NR) is commonly used to investigate the physical properties, which are dependent on the element in porous media, such as the distribution of water and mineral contents in ceramic, brick and concrete [3–5]. During petroleum exploration, it is proved that the transport property of thermal neutrons

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

(TN) can be used to identify the fluid types bearing in rock and soil [3, 6]. Moreover, NR is often taken as an effective non-destructive method in the research of pore structure. However, a few research studies have been reported to investigate the anisotropy of pore connectivity with TN in the last decade. Besides, many researchers believe that porosity computed with neutron data cannot be affected by the anisotropy. Therefore, a few research studies have been done to investigate the anisotropic transport of TN. Moreover, it is very difficult to study the anisotropy in the traditional rock experiment, because the intrinsic pore structure cannot be measured directly.

With the application of micron X-ray CT in digital rock physics (DRP) [7], the advantages of DRP in obtaining pore structure with a high resolution have made it an effective method to research properties of rock core. Based on DPR, static elastic and electrical properties can be simulated by the numerical methods, such as finite element and finite difference methods [8–10]. The lattice Boltzmann method had been used to simulate the transport of fluid in pore space for revealing the effects of micro-factors on permeability [11–13]. Besides, the research on the acoustic wave and the nuclear magnetic resonance can be efficiently conducted by the numerical simulation methods on the basis of digital rock model [14, 15]. However, since only matrix and pore [7, 16] can be segmented and taken as the effective contents, it is impossible to set up the distribution of chemical multi-components in conventional models. Therefore, little attention has been paid to the numerical research on the TN properties. Actually, the reaction between TN and material contents filling in matrix and pore will play a significant role in the study of thermal neutron transport. Accordingly, a new method has been proposed to construct a digital rock model including not only the three-dimensional pore structure, but also the material components. Thus, the transport of neutrons in the new models, considering the reactions between them and the components, can be simulated by the Monte Carlo method (MCM) for revealing the relationship between TN properties and the anisotropy of pore structure. Based on these results, the effects of the anisotropy on the evaluation of porosity can be further analysed through the neutron transport testing along different directions of the new models.

We use two categories of digital core samples obtained by micron X-ray CT [7, 17]. One group of rock image volumes is constructed from the carbonate (pure limestone) sample with the density of 2.63 gcm<sup>3</sup> . The other group is constructed from the pure sandstone with the density of 2.42 gcm<sup>3</sup> . The physical resolution of all digital core samples is 2.2046 μm per pixel, and the utilized facility is ultra XRM-L200. After cropping, we can get fourteen 400 400 400 carbonate cubes and a 400 400 400 sandstone cube for further property simulations. The composition of chemical elements in a real rock is so complicated that only the main elements can be considered in our research. Therefore, CaCO3 and H2O are set to represent the chemical components of matrix and pore-filling fluid in carbonate, respectively (pure limestone), whereas SiO2 and H2O are set to be the chemical components of matrix and porefilling fluid in sandstone, respectively. In both cases, these chemical contents are evenly distributed in their own space respectively.

For transport of thermal neutrons, the macroscopic reaction cross-section (MRCS) of polyatomic molecule can be written as

Physical Transport Properties of Porous Rock with Computed Tomography http://dx.doi.org/10.5772/intechopen.69415 233

$$
\Delta \Sigma = \frac{\rho N\_A}{A} \sum\_{i=1}^{n} l\_i \sigma\_i \tag{1}
$$

where Σ is the macroscopic reaction cross-section, cm�<sup>1</sup> ; <sup>ρ</sup> is the density of molecule, g�cm�<sup>3</sup> ; NA is the Avogadro constant, 6.02 � 1023; <sup>σ</sup><sup>i</sup> is the reaction cross-section of the <sup>i</sup>th atom for thermal neutron in the molecule, barn (10�<sup>24</sup> cm2 ); A is the molecular weight; n is the category number of atoms in the molecule and li is the number of the ith atom in the molecule.

(TN) can be used to identify the fluid types bearing in rock and soil [3, 6]. Moreover, NR is often taken as an effective non-destructive method in the research of pore structure. However, a few research studies have been reported to investigate the anisotropy of pore connectivity with TN in the last decade. Besides, many researchers believe that porosity computed with neutron data cannot be affected by the anisotropy. Therefore, a few research studies have been done to investigate the anisotropic transport of TN. Moreover, it is very difficult to study the anisotropy in the traditional rock experiment, because the intrinsic pore structure cannot be

With the application of micron X-ray CT in digital rock physics (DRP) [7], the advantages of DRP in obtaining pore structure with a high resolution have made it an effective method to research properties of rock core. Based on DPR, static elastic and electrical properties can be simulated by the numerical methods, such as finite element and finite difference methods [8–10]. The lattice Boltzmann method had been used to simulate the transport of fluid in pore space for revealing the effects of micro-factors on permeability [11–13]. Besides, the research on the acoustic wave and the nuclear magnetic resonance can be efficiently conducted by the numerical simulation methods on the basis of digital rock model [14, 15]. However, since only matrix and pore [7, 16] can be segmented and taken as the effective contents, it is impossible to set up the distribution of chemical multi-components in conventional models. Therefore, little attention has been paid to the numerical research on the TN properties. Actually, the reaction between TN and material contents filling in matrix and pore will play a significant role in the study of thermal neutron transport. Accordingly, a new method has been proposed to construct a digital rock model including not only the three-dimensional pore structure, but also the material components. Thus, the transport of neutrons in the new models, considering the reactions between them and the components, can be simulated by the Monte Carlo method (MCM) for revealing the relationship between TN properties and the anisotropy of pore structure. Based on these results, the effects of the anisotropy on the evaluation of porosity can be further analysed through the neutron transport testing along different directions of the

We use two categories of digital core samples obtained by micron X-ray CT [7, 17]. One group of rock image volumes is constructed from the carbonate (pure limestone) sample with the

pixel, and the utilized facility is ultra XRM-L200. After cropping, we can get fourteen 400 400 400 carbonate cubes and a 400 400 400 sandstone cube for further property simulations. The composition of chemical elements in a real rock is so complicated that only the main elements can be considered in our research. Therefore, CaCO3 and H2O are set to represent the chemical components of matrix and pore-filling fluid in carbonate, respectively (pure limestone), whereas SiO2 and H2O are set to be the chemical components of matrix and porefilling fluid in sandstone, respectively. In both cases, these chemical contents are evenly distributed

For transport of thermal neutrons, the macroscopic reaction cross-section (MRCS) of poly-

. The other group is constructed from the pure sandstone with the

. The physical resolution of all digital core samples is 2.2046 μm per

measured directly.

232 Computed Tomography - Advanced Applications

new models.

density of 2.63 gcm<sup>3</sup>

density of 2.42 gcm<sup>3</sup>

in their own space respectively.

atomic molecule can be written as

Table 1 shows the reaction cross-section of <sup>1</sup> <sup>1</sup>H, <sup>12</sup> <sup>6</sup> C, <sup>16</sup> <sup>8</sup> O, <sup>28</sup> <sup>14</sup>Si and <sup>40</sup> <sup>20</sup>Ca, where the first column is the abundance of primary elements, and the last column is the element abundance of their isotopes. Obviously, the abundance of the primary elements is the maximum and is commonly higher than 92%. Thus, it is reasonable for us to consider only these primary elements in our research. The density for the components CaCO3, SiO2 and H2O can be set to the value of 2.71, 2.65 and 1.00 g�cm�<sup>3</sup> , respectively, when the pressure is one standard atmosphere. MRCS of CaCO3, SiO2 and H2O will be: <sup>Σ</sup>CaCO3 <sup>¼</sup> 0.27, <sup>Σ</sup>SiO2 <sup>¼</sup> 0.20, <sup>Σ</sup>H2O <sup>¼</sup> 1.52 cm�<sup>1</sup> . Due to containing more hydrogen, MRCS of pore-filling fluid (H2O) is much larger than that of matrix (CaCO3 and SiO2). It is clear that porosity will have a significant influence on the transmission of incident neutrons [18], if the contents and the composition of rock model can keep unchanged. The transmittance will decrease with the increase of porosity, which can accordingly cause the change of the intensity of detected thermal neutron.

Figure 1 shows the two examples of the carbonate and the sandstone core sample, respectively. From Figure 1(b) and (d), it can be observed that the pore space is homogeneous in the sandstone core in YZ, XZ and XY planes, whereas the pore space is heterogeneous in a carbonate core in the three orthogonal planes. The cracks can observed in XZ and XY planes of the carbonate core (Figure 1(b)), but not in the YZ plane, which further demonstrates that its pore space is strongly anisotropic.

Neutrons can be classified into different types according to the energy level [19, 20], such as cold neutron, thermal and epithermal neutron. The energy of thermal neutrons involved in our


Table 1. Reaction cross-section of H, C, O, Si and Ca for thermal neutron and the corresponding natural abundance of isotopes.

Figure 1. 3D reconstructed pore structure of digital core based on micron X-ray CT. The total size of the dataset is 400 400 400 voxels with the edge length being 2.2046 μm. (a) The pore space of carbonate core, where the blue part is the pore structure; (b) the surface of the carbonate; (c) the pore distribution of sandstone, where the blue part is the pore structure; (d) the surface of the sandstone.

research is 0.0253 eV. In each simulation, these thermal neutrons will irradiate the constructed new models from a vertical direction of one surface plane. On another side of the model, we use array detectors to only receive the neutrons with the energy from 0.0250 to 0.0256 eV in order to record those unreacted thermal neutrons. Many parallel thermal neutron beams will randomly emit from the source (the green part in Figure 2) with the energy of 0.0253 eV for each neutron. The total amount of emitted neutrons is about 40 million moving from the source towards the

Figure 2. Model of thermal neutron irradiating core samples. The cube in the middle is the core sample; the plane on the left is the 50 � 50 array detector; the neutron source (square surface source) is at the right end of the lines. The detector, the model and the source are supposed to be in a straight line, and all of them are set under normal atmosphere. Moreover, they are of the same size in sections perpendicular to the line.

model. For the neutrons irradiating the core, some of them will react with the core model mostly via elastic scattering, which may change their energy and moving direction during these reactions. Meanwhile, those unreacted thermal neutrons can directly pass through the sample model and reach to the array detectors; therefore, their distribution can be recorded for further analysis and imaging. On the basis of above fact, we use the neutron transmission imaging method to obtain the distribution of difference of counts in YZ, XZ and XY planes.

### 2. Methods

research is 0.0253 eV. In each simulation, these thermal neutrons will irradiate the constructed new models from a vertical direction of one surface plane. On another side of the model, we use array detectors to only receive the neutrons with the energy from 0.0250 to 0.0256 eV in order to record those unreacted thermal neutrons. Many parallel thermal neutron beams will randomly emit from the source (the green part in Figure 2) with the energy of 0.0253 eV for each neutron. The total amount of emitted neutrons is about 40 million moving from the source towards the

Figure 1. 3D reconstructed pore structure of digital core based on micron X-ray CT. The total size of the dataset is 400 400 400 voxels with the edge length being 2.2046 μm. (a) The pore space of carbonate core, where the blue part is the pore structure; (b) the surface of the carbonate; (c) the pore distribution of sandstone, where the blue part is the pore

structure; (d) the surface of the sandstone.

234 Computed Tomography - Advanced Applications

#### 2.1. Reconstruction of core with X-ray CT

The method to reconstruct the digital rock model is based on micron meter X-ray CT imaging. Wilhelm Röntgen firstly found the X-ray in 1895, and X-ray CT was invented by Hounsfield and Cormack in 1979. Generally, the practical application of X-ray CT was in medical fields for scanning bone. Rapidly, it had spread into many fields [21], such as materials research and rock physics, as a non-destructive technique [17, 22]. For those monochromatic X-rays passing through the medium, some of them will react with the medium, which leads to the energy attenuation. Different components are of different attenuation coefficients, the transport process can be represented as below

$$I = I\_0 e^{-\int \mu(\mathbf{s}) d\_\ast} \tag{2}$$

where I<sup>0</sup> is the initial intensity of X-ray; I is the detected intensity after passing through the medium and μ(s) is the local attenuation coefficient along the transport paths. The components of a substance can be identified by measuring the attenuation coefficient of X-ray in experiments. For a cylindrical rock sample with diameter of a few millimetres or less, the resolution of X-ray CT can reach a few micron, or even better. The reconstruction of the new model used in our research can be divided into three steps including image acquisition, image processing and three-dimensional (3D) reconstruction. With micron X-ray CT instrument, lots of raw radiographs (as shown in Figure 3(a)) can be obtained through scanning a real rock sample, such as carbonate or sandstone core. Then, the radiographs will experience a series of processing before reconstruction, including noise reduction, smoothing, cropping and segmentation [7]. After that, the segmented binary data (400 400) with matrix and pore voxels (Figure 3(b)) can be achieved for each radiograph. Based on the binary data, the three-dimensional digital rock model can be reconstructed, which can allow us to consider both the pore structures, but also the material components, during the numerical simulation. The chemical component of pore-filling fluid is only water (H2O), whereas the component of matrix is only CaCO3 for carbonate and SiO2 for sandstone, respectively. Therefore, these different components will not anymore be considered as a uniform mixture according to the ratio of elements like that in the traditional methods. Instead, they are unevenly distributed in their own space in a form of completely separated.

The scale of the model should be optimized before simulation in order to reduce the consumption of time and computer memory. Therefore, we have utilized the representative elementary volume (REV) [23] method to implement the optimization by investigating the variety of porosity with the scale. The scale of REV can be determined when the porosity stops changing with the increase of model size. REV scale will give us the minimum elementary volume used to represent the whole sample in simulation. Actually, the specific REV is 400 400 400 voxels in our research.

#### 2.2. Lattice gas automata

The lattice gas automata (LGA) are derived from the cellular automata by improving the evolution and introducing the collision of particles. The complete discrete LGA model, named as the Hardy, Pomeau and de Pazzis (HPP) model, was introduced in 1973 to simulate the twodimensional (2D) fluids flow through dividing the computational field into square lattices. For

Figure 3. (a) Cross-sectional view of carbonate image with voxel of 2.2046 μm; (b) binary image with the blue areas representing the pore space and grey representing the matrix.

all LGA model, the discrete particles with unit mass and velocity are supposed to compose the fluid, they will move in the lattice following some local rules. At each step, the discrete particles will move forward one lattice unit to their neighbouring node along their headed directions. Then, they will undergo collisions following the rules that must conserve mass and momentum. Therefore, the local continuity and momentum conservation conditions can be satisfied for incompressible fluids in LGA. Due to the square shape of discrete lattice, the lattice tensor will be anisotropic in the HPP model, which may cause disagreement with the description of the Navier-Stokes Equation (NSE), and lead to some unreasonable simulating results consequently. A hexagon lattice was introduced in the Frisch, Hasslacher and Pomeau (FHP) model to simulate the viscous flow, which has six neighbouring nodes at each site for the particles to move after collision. With such lattices, the FHP model has successfully solved the asymmetric problem that is inherent in the HPP model.

In LGA, the evolution of distribution function of particle density can be used to describe the collision and streaming of particles, as follows:

$$f\_i(\mathbf{x} + e\_i, \ t + 1) = f\_i(\mathbf{x}, \ t) + \Omega(f\_i(\mathbf{x}, \ t)) \tag{3}$$

where the fi(x, t) represents the distribution function at node x, at time t, and moving along the direction i with the velocity of ei. The Ω represents the local rules utilized to control the redistribution of particles.

Based on the simple rules, the NSE for flow of an incompressible fluid could be retrieved at macro scale from the evolution of particle. Later, the improvement of FHP by introducing the rest particles makes the LGA method more reasonable for simulation of fluid flow.

#### 2.3. Lattice Boltzmann

such as carbonate or sandstone core. Then, the radiographs will experience a series of processing before reconstruction, including noise reduction, smoothing, cropping and segmentation [7]. After that, the segmented binary data (400 400) with matrix and pore voxels (Figure 3(b)) can be achieved for each radiograph. Based on the binary data, the three-dimensional digital rock model can be reconstructed, which can allow us to consider both the pore structures, but also the material components, during the numerical simulation. The chemical component of pore-filling fluid is only water (H2O), whereas the component of matrix is only CaCO3 for carbonate and SiO2 for sandstone, respectively. Therefore, these different components will not anymore be considered as a uniform mixture according to the ratio of elements like that in the traditional methods. Instead, they are unevenly distributed in their own space

The scale of the model should be optimized before simulation in order to reduce the consumption of time and computer memory. Therefore, we have utilized the representative elementary volume (REV) [23] method to implement the optimization by investigating the variety of porosity with the scale. The scale of REV can be determined when the porosity stops changing with the increase of model size. REV scale will give us the minimum elementary volume used to represent the whole sample in simulation. Actually, the specific REV is 400 400 400 voxels in our research.

The lattice gas automata (LGA) are derived from the cellular automata by improving the evolution and introducing the collision of particles. The complete discrete LGA model, named as the Hardy, Pomeau and de Pazzis (HPP) model, was introduced in 1973 to simulate the twodimensional (2D) fluids flow through dividing the computational field into square lattices. For

Figure 3. (a) Cross-sectional view of carbonate image with voxel of 2.2046 μm; (b) binary image with the blue areas

representing the pore space and grey representing the matrix.

in a form of completely separated.

236 Computed Tomography - Advanced Applications

2.2. Lattice gas automata

As a powerful and flexible approach for mesoscopic numerical simulation, especially in monophase and multi-phase fluid flow in porous medium, the lattice Boltzmann method (LBM) has been developed to a series of discrete space models including the two-dimensional model with multi-speed, since 1988. In the two-dimensional model (D2Q9), the square lattice with nine velocity vectors is used in discrete space of the computational domain and each node has eight neighbouring lattice nodes. At each time step, a particle at a node described by the distribution function of particle density moves to a neighbouring node, meanwhile, some particles move to this node together and undergo a collision at next time step to form a new distribution of particles.

The time evolution of LBM equation can be written as

$$f\_i(\mathbf{x} + \mathbf{e}\_i, t + 1) - f\_i(\mathbf{x}, t) = -\frac{1}{\tau} (f\_i(\mathbf{x}, t) - f\_i^{\text{eq}}(\mathbf{x}, t)), \text{ i } = 0, 1, 2, 3, \dots, 8 \tag{4}$$

where the fi(x, t) is the distribution function of particle density at lattice site x, time t, moving along the direction i with the velocity of ei. The τ is relaxation time and fi eq(x, t) is the equilibrium distribution of particles.

It was proved that the Navier-Stokes equation (NSE) can be derived from the time evolution of LBM in a mesoscopic scale using multi-scale and Champman-Enskog expansion technology with definition of density and momentum as the function of particle distribution and unit velocity vector, respectively.

$$\rho(\mathbf{x},t) = \sum\_{i=0}^{b} f\_i(\mathbf{x},t), \ \rho u(\mathbf{x},t) = \sum\_{i=0}^{b} f\_i(\mathbf{x},t)e\_i \tag{5}$$

#### 2.4. Monte Carlo method

The simulation for researching the transport and scatter of thermal neutrons in the model is conducted by the Monte Carlo method [24, 25] in our research. As a random or statistical method, the Monte Carlo method (MCM) is widely used in many physics fields, especially in nuclear physics. MCM has been proved that it can realistically model the experiment of nuclear physics [24, 25]. In this research, we focus on revealing the effects of elastic scattering on the transport of thermal neutron in the digital rock model. The neutrons moving in the medium will undergo several collisions to lose energy. Between every two collisions, they are supposed to transport along a straight line without loss of energy. Usually, it is composed of five key steps to determine the states during collisions, including setting up the initial state, locating the position, identifying atomic nucleus, determining collision type and measuring the direction and energy of neutrons after collision.

As described in Section 2.1, the constructed digital model, based on X-ray CT, consists of 400 � 400 � 400 pixel cubes containing the matrix and the pore space inside. Therefore, the model can give the projected image of 400 � 400 pixels in the YZ plane. In the image, the value of each pixel is porosity calculated with the 400 cubes along the X direction of the pixel. Thus, the projected image of porosity in the YZ plane can be used for a further analysis in our research. In the same way, the projected image of porosity in XZ and XY planes can be obtained, respectively. The same colour bar has been applied in the figures of both porosity image and the counts difference to eliminate the effects of the data magnitude, as shown in Figure 4. Accordingly, we can conveniently calculate the similarity between them in these figures by comparing each other. The pictures can be taken as two-dimensional matrices through converting them into grayscale, thus, the similarity between them can be computed by Eq. (6), as follows:

$$r = \frac{\sum\_{m} \sum\_{n} \left( A\_{mn} - \overline{A} \right) \left( B\_{mn} - \overline{B} \right)}{\sqrt{\left( \sum\_{m} \sum\_{n} \left( A\_{mn} - \overline{A} \right)^{2} \right) \left( \sum\_{m} \sum\_{n} \left( B\_{mn} - \overline{B} \right)^{2} \right)}} \tag{6}$$

where r represents the calculated similarity, Amn is the element value of matrix A, Bmn is the element value of matrix B, A is the average value of all elements in A and B is the average value of elements in B.

#### 2.5. Neutron imaging method

The elements of a material can be efficiently identified by the neutron transmission imaging method, which is generally taken as a non-destructive detection method in the past decades.

It was proved that the Navier-Stokes equation (NSE) can be derived from the time evolution of LBM in a mesoscopic scale using multi-scale and Champman-Enskog expansion technology with definition of density and momentum as the function of particle distribution and unit

The simulation for researching the transport and scatter of thermal neutrons in the model is conducted by the Monte Carlo method [24, 25] in our research. As a random or statistical method, the Monte Carlo method (MCM) is widely used in many physics fields, especially in nuclear physics. MCM has been proved that it can realistically model the experiment of nuclear physics [24, 25]. In this research, we focus on revealing the effects of elastic scattering on the transport of thermal neutron in the digital rock model. The neutrons moving in the medium will undergo several collisions to lose energy. Between every two collisions, they are supposed to transport along a straight line without loss of energy. Usually, it is composed of five key steps to determine the states during collisions, including setting up the initial state, locating the position, identifying atomic nucleus, determining collision type and measuring

As described in Section 2.1, the constructed digital model, based on X-ray CT, consists of 400 � 400 � 400 pixel cubes containing the matrix and the pore space inside. Therefore, the model can give the projected image of 400 � 400 pixels in the YZ plane. In the image, the value of each pixel is porosity calculated with the 400 cubes along the X direction of the pixel. Thus, the projected image of porosity in the YZ plane can be used for a further analysis in our research. In the same way, the projected image of porosity in XZ and XY planes can be obtained, respectively. The same colour bar has been applied in the figures of both porosity image and the counts difference to eliminate the effects of the data magnitude, as shown in Figure 4. Accordingly, we can conveniently calculate the similarity between them in these figures by comparing each other. The pictures can be taken as two-dimensional matrices through converting them into grayscale,

> <sup>n</sup> Amn � <sup>A</sup> � � Bmn � <sup>B</sup> � � ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi <sup>X</sup>

r � �

where r represents the calculated similarity, Amn is the element value of matrix A, Bmn is the element value of matrix B, A is the average value of all elements in A and B is the average value

The elements of a material can be efficiently identified by the neutron transmission imaging method, which is generally taken as a non-destructive detection method in the past decades.

m X

<sup>n</sup> Bmn � <sup>B</sup> � �<sup>2</sup>

ð6Þ

ð Þ x, t , <sup>ρ</sup>u x, t ð Þ¼ <sup>X</sup>

b

i¼0 f i ð Þ x, t ei ð5Þ

<sup>ρ</sup>ð Þ¼ x, t <sup>X</sup>

the direction and energy of neutrons after collision.

r ¼

of elements in B.

2.5. Neutron imaging method

b

i¼0 f i

thus, the similarity between them can be computed by Eq. (6), as follows:

X m X

<sup>n</sup> Amn � <sup>A</sup> � �<sup>2</sup> � � <sup>X</sup>

m X

velocity vector, respectively.

238 Computed Tomography - Advanced Applications

2.4. Monte Carlo method

Figure 4. Thermal neutron imaging of the core. The similarity of (a) and (b) is 0.8385; the similarity of (c) and (d) is 0.7322; the similarity of (e) and (f) is 0.8063. The resolution of (b), (d) and (f) is 17.6368 μm.

Hydrogen is the most effective neutron moderator, which mainly distributes in the pore-filling fluid (for example, water) as constituents of the rock. Therefore, the elastic scattering between thermal neutrons and hydrogen will mostly occur in the pore space. Thus, we can research the pore structure through detecting the neutron. The attenuation of monochromatic (single wavelength) neutron beam transporting in medium can be expressed as Eq. (7) [26, 27]

$$I = I\_0 e^{-\mu \tau} \tag{7}$$

where I is the intensity of neutron beam transporting in medium, I<sup>0</sup> is the initial intensity of incident neutron beam, μ is the attenuation coefficient, cm�<sup>1</sup> and τ is the sample thickness.

For the method, the key steps in simulation will be implemented following this process: pure matrix model without pore space, such as pure carbonate or sandstone, was first irradiated by TN beam to obtain the reference background. Then, the reconstructed digital rock (as shown in Figure 1) was put into the same environment for conducting the numerical experiment of simulating the transport of TN beam along directions of X-, Y- and Z-, respectively. Consequently, we can obtain the count difference through subtracting the simulated data of the reconstructed model, from that of the pure matrix model. Finally, we will image the distribution of count difference to further analyse the pore structure.

### 3. Results

#### 3.1. TN imaging of the model

Firstly, the carbonate model is selected for the numerical experiment. TN beam will irradiate the model along directions of X, Y and Z, respectively. The porosity images in YZ, XZ and XY planes have been, respectively, plotted in Figure 4(a), (c) and (e). Correspondingly, the count difference has been plotted in Figure 4(b), (d) and (f). As shown in Figure 4, the similarity of Figure 4(a) vs. (b), Figure 4(c) vs. (d) and Figure 4(e) vs. (f) can be calculated by Eq. (6), which can quantitatively verify that the new method is effective. The obvious count difference in Figure 4(b) can be observed in the middle and right part of the YZ plane, which is consistent with Figure 4(a). It is clear that the distribution of pore space in Figure 4(d) is uniform in the XZ plane of the model. A crack has been measured in Figure 4(f) in the XY plane. Therefore, it is intuitively observed that the distribution of porosity will obviously vary in different planes of the same model, according to Figure 4(b), (d) and (f). This observation can further demonstrate that the carbonate model has strong heterogeneity and anisotropy.

Ten cores were selected from the fourteen 400 � 400 � 400 carbonate model. For each core, we have conducted the numerical experiments and data processing along different directions, the corresponding count difference (CD) has been obtained, as shown in Figure 4(b), (d) and (f). On basis of this fact, the total count difference (TCD) and porosity can be calculated for each core. Relationship between TCD and total porosity has been constructed through linear fitting. The following equations are the relationship in different direction:

$$\text{Along X} - \text{direction}: \ \phi\_t = 1.62546589556 \times 10^{-7} \text{x} - 5.02730504255319 \times 10^{-4} \tag{8}$$

$$\text{Along Y} - \text{direction} : \phi\_t = 1.62519532496 \times 10^{-7} \text{x} - 5.73821908133962 \times 10^{-4} \qquad (9)$$

$$\text{Along Z} - \text{direction} : \phi\_t = 1.62543339256 \times 10^{-7} \text{x} - 4.24629774524067 \times 10^{-4} \tag{10}$$

where x represents the TCD obtained by the simulation along a given direction and φ<sup>t</sup> is the real total porosity of rock core. We have obtained three relationships between φ<sup>t</sup> and x along X, Y and Z directions, respectively, they are Eqs. (8)–(10). All the three fittings have the squared correlation coefficient <sup>R</sup><sup>2</sup> <sup>¼</sup> 0.99, which can demonstrate the reliability of them. It is clear that all the three equations are in good agreement with the simulated data. To verify the validity of the equations, they are utilized to predict porosity of the rest core samples. The TCD obtained along the X-direction will be substituted into Eqs. (8)–(10) to compute porosity of each core. The predicted results are shown in Table 2.

In Table 2, the first column is TCD obtained along the X-direction, and the second column is the real porosity of each core. The relative errors of predicted results with the three equations have been show in the next three columns, respectively. From the last three columns, it is observed that the relative errors of the predicted porosity will have small difference varying with the directions of neutron transport, when porosity is calculated by the three equations with the same simulated data. Therefore, it is reasonable to deduce that the linear relationship between TCD and porosity will be affected by the anisotropy, which is a contrast to the conventional conclusion.

The neutron transmission image in Figure 4 intuitively shows the distribution of pores, cracks and fractures in rock. On the basis of this fact, the heterogeneity and anisotropy of the model can be analysed with these images. In our research, the scale of array detectors will gradually vary from 4 � 4 to 400 � 400 for revealing the effects of resolution. It is the edge length of each detector in the array that can decide the resolution. Therefore, a variable range of resolution from 2.2046 to 220.46 μm can let us conveniently investigate the effects of the resolution on evaluation of anisotropy. Moreover, we repeat the numerical experiments on the carbonate core as shown in Figure 1 along the X-direction and record the results with the detector array of different resolution. Thus, a series of images with different resolutions can be obtained through processing the results, as shown in Figure 5. By comparing Figure 4(a) with Figure 5,


Table 2. Prediction of the porosity.

Hydrogen is the most effective neutron moderator, which mainly distributes in the pore-filling fluid (for example, water) as constituents of the rock. Therefore, the elastic scattering between thermal neutrons and hydrogen will mostly occur in the pore space. Thus, we can research the pore structure through detecting the neutron. The attenuation of monochromatic (single wave-

I ¼ I0e

where I is the intensity of neutron beam transporting in medium, I<sup>0</sup> is the initial intensity of incident neutron beam, μ is the attenuation coefficient, cm�<sup>1</sup> and τ is the sample thickness.

For the method, the key steps in simulation will be implemented following this process: pure matrix model without pore space, such as pure carbonate or sandstone, was first irradiated by TN beam to obtain the reference background. Then, the reconstructed digital rock (as shown in Figure 1) was put into the same environment for conducting the numerical experiment of simulating the transport of TN beam along directions of X-, Y- and Z-, respectively. Consequently, we can obtain the count difference through subtracting the simulated data of the reconstructed model, from that of the pure matrix model. Finally, we will image the distribu-

Firstly, the carbonate model is selected for the numerical experiment. TN beam will irradiate the model along directions of X, Y and Z, respectively. The porosity images in YZ, XZ and XY planes have been, respectively, plotted in Figure 4(a), (c) and (e). Correspondingly, the count difference has been plotted in Figure 4(b), (d) and (f). As shown in Figure 4, the similarity of Figure 4(a) vs. (b), Figure 4(c) vs. (d) and Figure 4(e) vs. (f) can be calculated by Eq. (6), which can quantitatively verify that the new method is effective. The obvious count difference in Figure 4(b) can be observed in the middle and right part of the YZ plane, which is consistent with Figure 4(a). It is clear that the distribution of pore space in Figure 4(d) is uniform in the XZ plane of the model. A crack has been measured in Figure 4(f) in the XY plane. Therefore, it is intuitively observed that the distribution of porosity will obviously vary in different planes of the same model, according to Figure 4(b), (d) and (f). This observation can further demon-

Ten cores were selected from the fourteen 400 � 400 � 400 carbonate model. For each core, we have conducted the numerical experiments and data processing along different directions, the corresponding count difference (CD) has been obtained, as shown in Figure 4(b), (d) and (f). On basis of this fact, the total count difference (TCD) and porosity can be calculated for each core. Relationship between TCD and total porosity has been constructed through linear fitting.

�μτ <sup>ð</sup>7<sup>Þ</sup>

length) neutron beam transporting in medium can be expressed as Eq. (7) [26, 27]

tion of count difference to further analyse the pore structure.

strate that the carbonate model has strong heterogeneity and anisotropy.

The following equations are the relationship in different direction:

3. Results

3.1. TN imaging of the model

240 Computed Tomography - Advanced Applications

Figure 5. Detection results of carbonate core with different resolution. (a) is a image with resolution 110.23 μm; (b) resolution 17.6368 μm; (c) resolution 2.2046 μm.

it is clear that a higher resolution does not always lead to a better image, which means that there is a critical resolution for the neutron imaging. Besides, the similarity (correlation coefficient) between the original model and the detected image has been computed by Eq. (6) under different resolutions. Figure 6(a) shows the calculated results, where the upper points and line represent the carbonate, the lower points and line represent the sandstone, the abscissa is the resolution and the ordinate is the similarity. According to Figure 6(a), it is observed that the similarity will be gradually improved with the increase of the resolution, then reach at the maximum resolution and rapidly decrease after that. Accordingly, we have developed a new equation to relate the resolution to the similarity as follows:

$$y = A\mathbf{x}^a e^{\mathbf{b}\mathbf{x}^a} - B \tag{11}$$

where x represents the resolution of array detector and y represents the similarity and A, B, a, b are constant parameters with related to the porous medium.

Specifically, the relation between the similarity and the resolution in Figure 6(a) can be written as

$$\text{Carbonate core}: \ y = 14.67 \text{x}^{-0.2554} e^{-1.951 \text{x}^{-0.284}} - 1.923, \ R^2 = 0.971 \tag{12}$$

$$\text{Sandstone core}: \ y = 0.1285x^{0.9649}e^{-0.0877x^{0.9649}} + 0.3025, \ R^2 = 0.984 \tag{13}$$

Obviously, Eq. (11) is suitable for both carbonate and sandstone, although they have different material compositions and pore distributions.

For the carbonate core, the simulation has been repeated eight times by modifying the amount of the emitted TN. Figure 6(b) shows the effect of the resolution on the similarity under different intensities of emitted neutron. From Figure 6(b), it is observed that the effect of the resolution on the similarity is similar with that in Figure 6(a), although the amount of emitted TN is different in each repeat. In order to make it clear, the rectangular zone is enlarged and is shown in the lower right of Figure 6(b). We can see that the peak of similarity will vary with the number of emitted TN. Generally, the peak will increase with increasing the TN number. However, the trend will stop when the TN number is more than 40 million. Moreover, it is

it is clear that a higher resolution does not always lead to a better image, which means that there is a critical resolution for the neutron imaging. Besides, the similarity (correlation coefficient) between the original model and the detected image has been computed by Eq. (6) under different resolutions. Figure 6(a) shows the calculated results, where the upper points and line represent the carbonate, the lower points and line represent the sandstone, the abscissa is the resolution and the ordinate is the similarity. According to Figure 6(a), it is observed that the similarity will be gradually improved with the increase of the resolution, then reach at the maximum resolution and rapidly decrease after that. Accordingly, we have developed a new equation to relate the

Figure 5. Detection results of carbonate core with different resolution. (a) is a image with resolution 110.23 μm; (b)

<sup>y</sup> <sup>¼</sup> Ax<sup>a</sup> e bxa

where x represents the resolution of array detector and y represents the similarity and A, B, a, b

Specifically, the relation between the similarity and the resolution in Figure 6(a) can be written as

Obviously, Eq. (11) is suitable for both carbonate and sandstone, although they have different

For the carbonate core, the simulation has been repeated eight times by modifying the amount of the emitted TN. Figure 6(b) shows the effect of the resolution on the similarity under different intensities of emitted neutron. From Figure 6(b), it is observed that the effect of the resolution on the similarity is similar with that in Figure 6(a), although the amount of emitted TN is different in each repeat. In order to make it clear, the rectangular zone is enlarged and is shown in the lower right of Figure 6(b). We can see that the peak of similarity will vary with the number of emitted TN. Generally, the peak will increase with increasing the TN number. However, the trend will stop when the TN number is more than 40 million. Moreover, it is

�1:951x�0:<sup>2554</sup>

�0:0877x0:<sup>9649</sup>

� B ð11Þ

� <sup>1</sup>:923, R<sup>2</sup> <sup>¼</sup> <sup>0</sup>:<sup>971</sup> <sup>ð</sup>12<sup>Þ</sup>

<sup>þ</sup> <sup>0</sup>:3025, R<sup>2</sup> <sup>¼</sup> <sup>0</sup>:<sup>984</sup> <sup>ð</sup>13<sup>Þ</sup>

resolution to the similarity as follows:

resolution 17.6368 μm; (c) resolution 2.2046 μm.

242 Computed Tomography - Advanced Applications

are constant parameters with related to the porous medium.

Carbonate core : <sup>y</sup> <sup>¼</sup> <sup>14</sup>:67x�0:<sup>2554</sup><sup>e</sup>

Sandstone core : <sup>y</sup> <sup>¼</sup> <sup>0</sup>:1285x<sup>0</sup>:<sup>9649</sup><sup>e</sup>

material compositions and pore distributions.

Figure 6. The resolution and the number of thermal neutrons emitted in each simulation.

observed that the peak only appears in a range of the resolution from 10 to 20 μm. Currently, the maximum physical resolution for array detector is about 15 μm [20]. However, based on our results under the condition of 40 million TN, the optimum resolution of array detectors should be set to 17.6368 μm for carbonate in our research.

#### 3.2. Simulations for electrical transport properties

In order to investigate the electrical transport properties, LGA has been applied to simulate the current flow in digital rock samples virtually saturated with oil and water, for revealing the relationship between resistivity index and water (oil) saturation (I-Sw) at a pore scale. Based on the digital core, we use LGA to research the variation of the resistivity with the saturation for investigating the origin of the non-Archie I-Sw relation. The simulated results indicate that I-Sw relation is a non-linear function in a log-log plot, which is a contrast to the Archie's formula. With the decreasing of water saturation and porosity, the I-Sw relation will gradually turn towards the abscissa (water saturation axis), which means a non-Archie phenomenon appears in a low saturation zone. In this case, Archie's formula is valid only when the water saturation is in a high zone. Therefore, a new equation has been developed to describe the non-Archie I-Sw relation based on this study, which can be used to improve the accuracy of saturation calculation in reservoir evaluation. The calculated results with the new equation have shown that it may fit the data of laboratory measurements very well.

Figure 7. The non-linear relation of I-Sw for water saturation from 0.1 to 1.

In Figure 7, the horizontal axis is the water saturation. The vertical axis is the resistivity index. The range of the water saturation applied in the numerical simulation is set to span from 0.1 to 1 to further investigate the widely changing of the I-Sw relation. Figure 7 shows I-Sw relation obtained by the virtual experiments of LGA on the digital rock models, with decreasing water saturation to below 0.3. In this figure, the non-linear I-Sw relation can be obviously observed, especially when the water saturation is less than 0.3. In a log-log plot, I-Sw relation will gradually drop off towards the abscissa with decreasing Sw. Therefore, it is reasonable to deduce that the Archie exponent n is a function of Sw, instead of a constant in Archie's theory.

### 3.3. Simulation of fluid flow by LBM

observed that the peak only appears in a range of the resolution from 10 to 20 μm. Currently, the maximum physical resolution for array detector is about 15 μm [20]. However, based on our results under the condition of 40 million TN, the optimum resolution of array detectors

In order to investigate the electrical transport properties, LGA has been applied to simulate the current flow in digital rock samples virtually saturated with oil and water, for revealing the relationship between resistivity index and water (oil) saturation (I-Sw) at a pore scale. Based on the digital core, we use LGA to research the variation of the resistivity with the saturation for investigating the origin of the non-Archie I-Sw relation. The simulated results indicate that I-Sw relation is a non-linear function in a log-log plot, which is a contrast to the Archie's formula. With the decreasing of water saturation and porosity, the I-Sw relation will gradually turn towards the abscissa (water saturation axis), which means a non-Archie phenomenon appears in a low saturation zone. In this case, Archie's formula is valid only when the water saturation is in a high zone. Therefore, a new equation has been developed to describe the non-Archie I-Sw relation based on this study, which can be used to improve the accuracy of saturation calculation in reservoir evaluation. The calculated results with the new equation have shown

should be set to 17.6368 μm for carbonate in our research.

that it may fit the data of laboratory measurements very well.

Figure 7. The non-linear relation of I-Sw for water saturation from 0.1 to 1.

3.2. Simulations for electrical transport properties

244 Computed Tomography - Advanced Applications

The numerical experiments involved in this study are modelling the flow of Newtonian fluid in a three-dimensional channel with rigid boundaries at the top and bottom. For a stationary flow driven by a constant horizontal pressure gradient, if the velocity is sufficiently low to neglect the inertia terms, the NS equation can be simplified to Darcy's law, i.e.

$$Q = \text{K\nabla P/}\mu\tag{14}$$

where Q is the volume flow rate in unit of m/s, K is the permeability of the medium in unit of m2 and μ is the dynamic viscosity of the fluid.

Single-phase flow in pore space has been simulated by LBM with a digital rock of 400 � 400 � 400 voxels. The distribution of fluid velocity is plotted in Figure 8. In order to clearly show the distribution inside the rock, only slices had been chosen to draw in the figure.

Based on the simulations, the absolute permeability can be calculated with Eq. (3). After comparing the results with experimental data, it is proved the feasibility and validity of LBM

Figure 8. Velocity distribution profile of 3D digital rock model.

in the research of simulating fluid transport properties at the pore scale. Moreover, the phenomenon of oil-water two-phase flow can be simulated by introducing the Shan-Chen potential model.

### 4. Discussion

On the basis of the digital core, LGA was utilized to simulate the variation of resistivity with the saturation for revealing the origin of the non-Archie I-Sw relation. The simulated results further verify that I-Sw relation is a non-linear function in a log-log plot, which is a contrast to Archie's formula. Furthermore, we have proved that Archie's formula is valid only when the water saturation is in a high zone, and the exponent n is a function of Sw, instead of a constant in Archie's theory. Moreover, the flow of single-phase Newtonian fluid in a three-dimensional digital rock had been implemented with LBM for calculating the absolute permeability. The good agreement between the calculated results and the experimental data has further proved the validity of LBM in research of fluid flow in pore space.

A new method has been developed to reconstruct a digital rock model based on the data from scanning a real rock with micron X-ray CT, which can simultaneously take into account both the pore structure and the material components. MCM is used to simulate the transport of TN in medium at a pore scale. After analysing the results, we have further investigated the effect of anisotropy on the porosity calculation. According to the results, it is proved that the method of TN imaging can intuitively show the distribution of pore, cracks and fractures inside a rock. Moreover, we have found that the linear relationship between TCD and total porosity can be slightly affected by the anisotropy. Therefore, porosity may have a little difference if the data of different directions are utilized, when we use the neutron method to evaluate porosity of porous media. In the new model, the distribution of chemical elements of different components is supposed to be uniform in their space, such as in matrix or in pore space. Hydrogen, as the most effective neutron moderator, mainly distributes in pore-filling fluids, such as water, oil and natural gas. Thus, the content and distribution of these substances in rock can be quantitatively investigated with the neutron method. The results of our research may offer an evident to support the anisotropic analysis of pore structure with the neutron method. Furthermore, the distribution of substances containing hydrogen-4 is of great interest in many research fields, which is mainly detected by the neutron radiography at present. Accordingly, our new method may be a significant reference for them due to its flexible ability in handling complex pore structure and components distribution. Besides, we have found that a higher resolution of array detector cannot always lead to a better neutron image, when we research the pore connectivity and distribution with TN transmission. A critical resolution for the optimum image can be determined with our method, under the condition of a suitable TN number emitted in each simulation.

### Acknowledgements

The authors thank financial supports from the National Natural Science Foundation of China (Grant Nos. 41374143 and 41074103).

### Author details

in the research of simulating fluid transport properties at the pore scale. Moreover, the phenomenon of oil-water two-phase flow can be simulated by introducing the Shan-Chen potential

On the basis of the digital core, LGA was utilized to simulate the variation of resistivity with the saturation for revealing the origin of the non-Archie I-Sw relation. The simulated results further verify that I-Sw relation is a non-linear function in a log-log plot, which is a contrast to Archie's formula. Furthermore, we have proved that Archie's formula is valid only when the water saturation is in a high zone, and the exponent n is a function of Sw, instead of a constant in Archie's theory. Moreover, the flow of single-phase Newtonian fluid in a three-dimensional digital rock had been implemented with LBM for calculating the absolute permeability. The good agreement between the calculated results and the experimental data has further proved

A new method has been developed to reconstruct a digital rock model based on the data from scanning a real rock with micron X-ray CT, which can simultaneously take into account both the pore structure and the material components. MCM is used to simulate the transport of TN in medium at a pore scale. After analysing the results, we have further investigated the effect of anisotropy on the porosity calculation. According to the results, it is proved that the method of TN imaging can intuitively show the distribution of pore, cracks and fractures inside a rock. Moreover, we have found that the linear relationship between TCD and total porosity can be slightly affected by the anisotropy. Therefore, porosity may have a little difference if the data of different directions are utilized, when we use the neutron method to evaluate porosity of porous media. In the new model, the distribution of chemical elements of different components is supposed to be uniform in their space, such as in matrix or in pore space. Hydrogen, as the most effective neutron moderator, mainly distributes in pore-filling fluids, such as water, oil and natural gas. Thus, the content and distribution of these substances in rock can be quantitatively investigated with the neutron method. The results of our research may offer an evident to support the anisotropic analysis of pore structure with the neutron method. Furthermore, the distribution of substances containing hydrogen-4 is of great interest in many research fields, which is mainly detected by the neutron radiography at present. Accordingly, our new method may be a significant reference for them due to its flexible ability in handling complex pore structure and components distribution. Besides, we have found that a higher resolution of array detector cannot always lead to a better neutron image, when we research the pore connectivity and distribution with TN transmission. A critical resolution for the optimum image can be determined with our

method, under the condition of a suitable TN number emitted in each simulation.

The authors thank financial supports from the National Natural Science Foundation of China

the validity of LBM in research of fluid flow in pore space.

model.

4. Discussion

246 Computed Tomography - Advanced Applications

Acknowledgements

(Grant Nos. 41374143 and 41074103).

Wenzheng Yue\* and Yong Wang

\*Address all correspondence to: yuejack1@sina.com

State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China

### References


**Section 3**

## **Life Sciences**

[13] Chen L, et al. Nanoscale simulation of shale transport properties using the lattice

[14] Knackstedt MA, Latham S, Madadi M, Sheppard A, Varslot T Arns CH. Digital rock physics: 3D imaging of core material and correlations to acoustic and flow properties.

[15] Wang KW, Li N. Numerical simulation of rock pore-throat structure effects on NMR T2

[17] Fredrich JT, Menéndez B, Wong TF. Imaging the pore structure of geomaterials. Science.

[18] Wu W, Tong M, Xiao L, Wang J. Porosity sensitivity study of the compensated neutron

[19] Carron NJ. An Introduction to the Passage of Energetic Particles Through Matter. Park

[21] Banhart J, et al. Advanced Tomographic Methods in Materials Research and Engineering.

[22] Mees F, Swennen R, Geet MV, Jacobs P. Applications of X-ray computed tomography in the geosciences. Geological Society, London. Special Publications. 2003;215:1

[23] Vik B, Bastesen E, Skauge A. Evaluation of representative elementary volume for a vuggy

[24] Carter LL, Cashwell ED. Particle Transport Simulation with the Monte Carlo Method. United States: Technical Information Center, Office of Public Affairs, U. S. Energy

[25] Lux I, Koblinger L. Monte Carlo Particle Transport Methods: Neutron and Photon Calcu-

[26] Herman M, et al. Evaluated Nuclear Data File (ENDF) Retrieval & Plotting. National Nuclear Data Center [Internet]. 2015. Available from: http://www.nndc.bnl.gov/sigma/

[27] Nuclear Wallet Cards. National Nuclear Data Center [Internet]. 2015. Available from: http://www.nndc.bnl.gov/nudat2/indx\_sigma.jsp [Accessed: 15 August 2015]

—Part: Porosity, permeability, and dispersivity. Journal of Petroleum Sci-

spatial resolution. Nuclear Instruments and Methods in Physics Research Section A.

[20] Tremsin AS, et al. On the possibility to image thermal and cold neutron with sub-15

logging tool. Journal of Petroleum Science and Engineering. 2013;108:10

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[16] Andrä H, et al. Digital rock physics benchmarks

Drive, UK: Taylor & Francis Group; 2006. pp. 308

Oxford, UK: Oxford University Press; 2008

Research and Development Administration; 1975. p. 1

lations. Florida, USA: CRC Press, Inc.; 1991

### **Chapter 12**

## **Vascular and Cardiac CT in Small Animals**

Giovanna Bertolini and Luca Angeloni

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69848

#### **Abstract**

Computed tomography (CT) is increasingly available in veterinary practice. As for humans, CT has a tremendous potential in various clinical scenario. Oncology and traumatized dogs and cats are probably the veterinary patients that get more benefit from new CT appli‐ cations. However, the most amazing progresses are in vascular and cardiac applications. The advent and rapid diffusion of advanced scanner technology (multidetector row) offer unparalleled diagnostic opportunity in daily practice for comprehensive evaluation of com‐ plex cardiovascular diseases. New skills and knowledge are necessary for radiologists and nonradiologists for understanding this revolutionary field of radiology.

**Keywords:** CT angiography, cardiac CT, vascular anomalies, portosystemic shunt, vascular ring anomalies, cardiac diseases

### **1. Introduction**

Computed tomography (CT) is a cross‐sectional imaging modality based on the absorption of X‐rays in the patient. The overall performance of a CT system depends on several key compo‐ nents, comprising the X‐ray source, a high‐powered current generator, number of detectors, detector electronics, data transmission systems, and the computer system for image pre and post processing [1]. CT angiography (CTA) first became possible with the advent of spiral CT in the early 1980s, which combined simultaneous continuous gantry rotation and table move‐ ment, succeeding the axial or step‐and‐shoot acquisition mode of conventional CT scanners [2, 3]. In this manner, the tube‐detector system takes a helical or spiral path around the patient moving through the gantry while the detectors collect the data. The *x*‐*y* plane is the plane of the slice, whereas the *z* direction is along the axis of the patient (**Figure 1**).

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Figure 1.** Schematization of in plane, longitudinal resolution, and isotropic voxel.

The scan volume is composed of thousands of volume elements (voxels). Ideally, for high‐quality images, voxels should be of equal dimensions in all three spatial axes (*x*‐*y*‐*z*), so that the spatial resolution is isotropic, which means equal in all directions.

The *isotropic resolution* is a fundamental prerequisite for high‐quality vascular studies and post‐ processing reconstruction. The *temporal resolution* is the second essential requirement for vascular and cardiac CT studies. Larger volume coverage with isotropic resolution and high temporal resolution (fast scanning) was not possible using single‐detector spiral CT. For this, at the end of the 1990s, all major manufacturers introduced the first generation of (MDCT) systems, having 4 rows of detectors and systems with 8, 10, and 16 detector arrays became available after few years. The 4‐ and 8‐slice systems still showed inherent limitations regarding scan times and had limited *z*‐axis resolution (with fully isotropic acquisition being possible for limited body volume). The advent of 16‐MDCT scanners in 2001 represented a breakthrough in medical imaging, allow‐ ing routine scanning of larger volumes with true isotropic, submillimeter spatial resolution. 16‐ MDCT transformed CT from a transaxial cross‐sectional technique into a truly three‐dimensional (3D) imaging modality. This technology, still largely available in veterinary practice, has been overwhelmed in human field and in most advanced veterinary centers by newer CT scanners with 64, 128, 256, and 320 detector rows. Compared with 4‐MDCT scanners, the performance of 64‐MDCT scanners has increased more than 20 times, due to the increase in the number of detec‐ tor rows and rotation [4]. The most recent dual‐source CT scanner (DSCT), which features two tube‐detector arrays, can achieve a rotation time of up to 0.25 s and a volume coverage speed of up to 737 mm/s [5]. Voluntary breath holding is not possible in veterinary patients as it is in con‐ scious adult human patients. Thus, veterinary patients are usually anesthetized and intubated during the scans. The reduced data acquisition time of faster MDCT scanners and DSCT results in shorter anesthesia or, in selected cases, in decreased need of anesthesia.

### **2. Principles of MDCT angiography**

The scan volume is composed of thousands of volume elements (voxels). Ideally, for high‐quality images, voxels should be of equal dimensions in all three spatial axes (*x*‐*y*‐*z*), so that the spatial

The *isotropic resolution* is a fundamental prerequisite for high‐quality vascular studies and post‐ processing reconstruction. The *temporal resolution* is the second essential requirement for vascular and cardiac CT studies. Larger volume coverage with isotropic resolution and high temporal resolution (fast scanning) was not possible using single‐detector spiral CT. For this, at the end of the 1990s, all major manufacturers introduced the first generation of (MDCT) systems, having 4 rows of detectors and systems with 8, 10, and 16 detector arrays became available after few years. The 4‐ and 8‐slice systems still showed inherent limitations regarding scan times and had limited *z*‐axis resolution (with fully isotropic acquisition being possible for limited body volume). The advent of 16‐MDCT scanners in 2001 represented a breakthrough in medical imaging, allow‐ ing routine scanning of larger volumes with true isotropic, submillimeter spatial resolution. 16‐ MDCT transformed CT from a transaxial cross‐sectional technique into a truly three‐dimensional (3D) imaging modality. This technology, still largely available in veterinary practice, has been overwhelmed in human field and in most advanced veterinary centers by newer CT scanners with 64, 128, 256, and 320 detector rows. Compared with 4‐MDCT scanners, the performance of 64‐MDCT scanners has increased more than 20 times, due to the increase in the number of detec‐ tor rows and rotation [4]. The most recent dual‐source CT scanner (DSCT), which features two tube‐detector arrays, can achieve a rotation time of up to 0.25 s and a volume coverage speed of up to 737 mm/s [5]. Voluntary breath holding is not possible in veterinary patients as it is in con‐ scious adult human patients. Thus, veterinary patients are usually anesthetized and intubated

resolution is isotropic, which means equal in all directions.

**Figure 1.** Schematization of in plane, longitudinal resolution, and isotropic voxel.

252 Computed Tomography - Advanced Applications

The simultaneous acquisition of several sections not only results in an extremely increased scan speed but also in an extension of the CT scan range with isotropic resolution, which allow for reconstructing images in any arbitrary plane without loss of image quality. When properly used, MDCT scanners can provide high‐quality three‐dimensional (3D) mapping of the vascu‐ lature, allowing simultaneous evaluation of the vascular lumen, as well as the vessel wall and surrounding structures. Contrast medium (CM) is essential for CT angiography (CTA). In our patients, CM is usually injected through an intravenous catheter placed in a peripheral vein. When injected, CM reaches the heart and then travels throughout the body in the cardiovas‐ cular circulation. The goal of CTA is to achieve adequate opacification (magnitude of contrast enhancement) in the vascular territory of interest, within a certain time (timing of CM), and to maintain a consistent level of enhancement throughout scanning (shaping of CM) [6, 7]. CM concentration and injection protocol need to be adapted to the patient characteristics, the vas‐ cular territory of interest, and to take advantage of the capabilities of the MDCT scanner used. Intravascular attenuation of at least 300–400 HU along the full longitudinal extent of the target vasculature and throughout the duration of acquisition is considered to be a prerequisite for high‐quality CTA. Vascular contrast enhancement is influenced by various interacting factors: (1) patient‐related factors, (2) CM‐related factors, and (3) MDCT scanner‐related factors.

Principal patient factors that affect vascular enhancement are cardiac output and body weight. Veterinary patients have wide ranges of body weight and heartbeat. Thus, when designing a CTA protocol, it is essential to consider these characteristics to achieve high‐quality results consistently [8, 9]. In particular, the body weight is the most important patient‐related fac‐ tor affecting the magnitude of contrast enhancement in vascular studies (they are inversely related). Interindividual variability in vascular contrast enhancement may be reduced by adjusting the overall iodine dose (by increasing CM volume and/or iodine concentration) and by increasing the injection rate proportional to body weight. The timing of CM is influenced by the cardiac output (inversely related). In patients with normal cardiac output, peak arte‐ rial contrast enhancement is achieved shortly after CM injection. In patients with decreased cardiac output, CM is distributed and clears slowly, leading to delayed and persistent peak arterial enhancement. In patients with higher cardiac output (small/toy breeds and cats or larger patients with diseases such as anemia or sepsis), CM distribution is unpredictable. A fixed scan delay is not recommended for CTA in veterinary patients.

Two methods are possible to predict how CM will behave in a given patient (injection indi‐ vidualization): (1) test bolus and (2) automated bolus triggering or bolus tracking. For the test bolus method, a small amount of CM is injected and multiple low‐dose nonincremental scans are taken over the region of interest (ROI) until the contrast is visualized in the selected vessel. For first generations of MDCT scanners (4–8 MDCT), this time can be used directly as the scanning delay for subsequent CTA. When using faster MDCT scanners, however, an additional time must be calculated to obtain a diagnostic delay, considering the scan speed, to not "outrun" the CM bolus. Using bolus‐triggering technique, test bolus injection is not neces‐ sary. All state‐of‐art MDCT systems feature this option. Multiple images are obtained over the ROI in a nonincremental manner during CM injection and the scan is initiated automatically when the density within the vessel exceeds a predetermined Hounsfield unit (HU) value.

A mechanical power injector is essential for MDCT angiography. This device allows pre‐ programming of the CM volume and flow rate and the setting of an injection pressure limit. Injection protocol parameters that may influence the opacification of target vessels are (1) injection duration (volume:rate), (2) rate of injection, and (3) volume of CM injected (duration × rate). In particular, arterial enhancement depends on the flow rate (mL/s). When the whole CM bolus is delivered at a constant injection rate (uniphasic injection), there is an upslope and downslope of the CM distribution curve and the vascular enhancement may be not uniform during volume acquisition [10, 11]. This characteristic is less important for short scan ranges (e.g., CTA of the liver, pancreas, etc.) or with newer fast scanners, but may be problematic when scanning larger vascular territories (e.g., aortoiliac CTA) or using slower CT scanners. Biphasic injection (a rapid phase, followed by a second slower phase) and multiphasic, exponentially decelerating techniques (multiphasic‐rate injection bolus with exponentially decreasing rate) provide more uniform enhancement with a longer plateau phase and may be indicated for larger volume coverage using slow scanners. In our experience, saline flushing following uni‐ phasic CM bolus using same rate and of half‐to‐same volume (using a dual‐barrel injector system) effectively improves contrast distribution in the vascular system during acquisition.

### **3. MDCTA of vascular diseases**

MDCT has brought about dramatic changes in veterinary vascular imaging during the past decade, leading to once unconceivable noninvasive diagnostic possibilities. Nowadays, CT‐angiography is reported to be the method of choice for *in vivo* vascular anatomy depiction and for the diagnosis of various vascular pathological conditions [12–15]. A wide spectrum of vascular thoracic and abdominal disorder may be studied with MDCT angiography. MDCT angiographic studies are frequently used for detailed assessment and interventional planning in case of congenital and acquired vascular thoracic or abdominal anomalies. Other indica‐ tions for MDCTA include vascular thrombosis and trauma.

### **3.1. Thoracic CTA applications**

The thoracic vascularization includes systemic vasculature and pulmonary vessels. Systemic arte‐ rial thoracic vasculature is provided by branches of the thoracic aorta. The pulmonary arteries supply 99% of the blood flow to the lungs and participate in gas exchange at the alveolar capillary membrane, while the bronchial branches of the bronchoesophageal artery supply the supporting structures of the lungs, including the pulmonary arteries. The pulmonary and bronchial arteries have rich and complex anastomoses at the capillary level. The venous drainage of the thorax is provided by cranial vena cava and azygos vein system. CM distribution after peripheral intra‐ venous injection differs among the heart and the systemic and pulmonary arteries and veins, and this should be considered when designing a CT protocol. The delay between the start of CM injection and the initiation of scanning should be tailored based on scanner performance and the patient's characteristics (using the bolus test or the bolus tracking technique, as said before). The ROI will be placed on different vascular structures, the aorta, or the main pulmonary artery, depending on the clinical purpose. Clinical indications for MDCTA of the thorax include anoma‐ lies of the aortic arch and its branches, bronchial and bronchoesophageal arterial anomalies, and systemic thoracic veins diseases [16–18]. Pulsatile artifacts are critical for the accurate diagnosis of aortic arch anomalies, especially in small veterinary patients. With slower 8–16‐MDCT scanners, acquisition of near‐isotropic dataset with spiral acquisition mode and a half‐scan interpolation reconstruction (50% overlap) algorithm aid the distinction between motion artifacts and intrinsic disease. Scanners with 40 or more rows can routinely imaging of the thoracic aorta using electro‐ cardiogram (ECG) gating. At our center, which is equipped currently with a second‐generation DSCT scanner, all CT examinations of patients with suspected or known aortic arch pathologies or other cardiovascular anomalies are now ECG‐gated or acquired in sub‐second flash spiral mode, resulting in the freezing of cardiovascular and respiratory motions.

Most vascular ring anomalies found in dogs are *persistent right aortic arch* (PRAA) with left‐sided ligamentum arteriosum, with the heart base making up the ventral portion of the ring. PRAA has been described associated with patent ductus arteriosus (PDA). One‐third of dogs with PRAA also have an *aberrant left subclavian artery* that may take a retroesophageal position, contributing to esophageal compression. The *right aberrant subclavian artery* arises from the normally left‐sided aortic arch, distal to the left subclavian artery, or from a bisubclavian trunk is generally reported incidentally (**Figure 2**).

Enlarged bronchial branches of bronchoesophageal artery (*bronchoesophageal artery hypertro‐ phy (BEAH)*) and other nonbronchial thoracic arteries (e.g., intercostal, internal mammary, and inferior phrenic arteries) are frequently observed in patients with chronic pulmonary embolism. These vessels respond to chronic pulmonary ischemia and decreased pulmonary blood flow with hypertrophy or enlargement, trying to maintain blood flow to the affected lung and participate in gas exchange through the peripheral systemic‐pulmonary arterial anastomoses. Thoracic CTA show prominent bronchial branches at the bronchial bifurcation, continuing their course along the bronchi, describing a tortuous path, and ultimately anasto‐ mose with the subsegmental pulmonary arteries (**Figure 3**).

**Figure 2.** Right aberrant subclavian artery. E, esophagus.

additional time must be calculated to obtain a diagnostic delay, considering the scan speed, to not "outrun" the CM bolus. Using bolus‐triggering technique, test bolus injection is not neces‐ sary. All state‐of‐art MDCT systems feature this option. Multiple images are obtained over the ROI in a nonincremental manner during CM injection and the scan is initiated automatically when the density within the vessel exceeds a predetermined Hounsfield unit (HU) value.

A mechanical power injector is essential for MDCT angiography. This device allows pre‐ programming of the CM volume and flow rate and the setting of an injection pressure limit. Injection protocol parameters that may influence the opacification of target vessels are (1) injection duration (volume:rate), (2) rate of injection, and (3) volume of CM injected (duration × rate). In particular, arterial enhancement depends on the flow rate (mL/s). When the whole CM bolus is delivered at a constant injection rate (uniphasic injection), there is an upslope and downslope of the CM distribution curve and the vascular enhancement may be not uniform during volume acquisition [10, 11]. This characteristic is less important for short scan ranges (e.g., CTA of the liver, pancreas, etc.) or with newer fast scanners, but may be problematic when scanning larger vascular territories (e.g., aortoiliac CTA) or using slower CT scanners. Biphasic injection (a rapid phase, followed by a second slower phase) and multiphasic, exponentially decelerating techniques (multiphasic‐rate injection bolus with exponentially decreasing rate) provide more uniform enhancement with a longer plateau phase and may be indicated for larger volume coverage using slow scanners. In our experience, saline flushing following uni‐ phasic CM bolus using same rate and of half‐to‐same volume (using a dual‐barrel injector system) effectively improves contrast distribution in the vascular system during acquisition.

MDCT has brought about dramatic changes in veterinary vascular imaging during the past decade, leading to once unconceivable noninvasive diagnostic possibilities. Nowadays, CT‐angiography is reported to be the method of choice for *in vivo* vascular anatomy depiction and for the diagnosis of various vascular pathological conditions [12–15]. A wide spectrum of vascular thoracic and abdominal disorder may be studied with MDCT angiography. MDCT angiographic studies are frequently used for detailed assessment and interventional planning in case of congenital and acquired vascular thoracic or abdominal anomalies. Other indica‐

The thoracic vascularization includes systemic vasculature and pulmonary vessels. Systemic arte‐ rial thoracic vasculature is provided by branches of the thoracic aorta. The pulmonary arteries supply 99% of the blood flow to the lungs and participate in gas exchange at the alveolar capillary membrane, while the bronchial branches of the bronchoesophageal artery supply the supporting structures of the lungs, including the pulmonary arteries. The pulmonary and bronchial arteries have rich and complex anastomoses at the capillary level. The venous drainage of the thorax is provided by cranial vena cava and azygos vein system. CM distribution after peripheral intra‐ venous injection differs among the heart and the systemic and pulmonary arteries and veins,

**3. MDCTA of vascular diseases**

254 Computed Tomography - Advanced Applications

**3.1. Thoracic CTA applications**

tions for MDCTA include vascular thrombosis and trauma.

**Figure 3.** Acquired pattern of BEAH in a dog with chronic bronchopulmonary disease. A. Thin volume‐rendered image of the thorax (the head is on the right). The arrow indicates the enlarged bronchoesophageal artery. B. Arrows indicate hypertrophied subsegmental bronchial arteries coursing along the corresponding bronchus.

*Congenital pattern of BEAH* is described in dogs in association with systemic‐to‐pulmonary fistula (with left or right main pulmonary artery) [17, 18]. This pattern might result from per‐ sistent embryonic pulmonary‐systemic connection, as hypothesized for PDA. In these cases, a large vessel (5–8 mm diameter) is seen in middle mediastinum, emptying into the proximal part of the left or right pulmonary artery through a small orifice. A dense periesophageal vascular network accompanies the congenital form of BEAH (**Figure 4**).

A *persistence of the left cranial vena cava* (CrVC) is probably the most common thoracic venous anomalies in our patients [19]. Persistent left CrVC alone is often an incidental CT finding, but may cause esophageal stenosis and may be associated with severe cardiovascular defects.

**Figure 4.** Congenital pattern of bronchoesophageal artery hypertrophy with artery‐to‐pulmonary fistula (not visible here). Note the enlarged bronchoesophageal artery arising from the thoracic aorta and the dense mediastinal vascular network (dorsal view).

The left persistent CrVC results from incomplete atrophy of the embryonic left cranial cardi‐ nal vein. Two types are described in dogs and cats: (1) a complete type, with nonatrophied left cranial cardinal vein retaining its embryological connection with the coronary sinus; (2) an incomplete type, in which the distal portion of the persistent vein atrophies, whereas the proximal portion persists and receives the hemiazygos vein.

In oncology patients, MDCTA is indicated for the assessment and interventional planning in case of mediastinal masses or tumors of the thoracic wall involving the thoracic vasculature.

### **3.2. Abdominal vascular diseases**

*Congenital pattern of BEAH* is described in dogs in association with systemic‐to‐pulmonary fistula (with left or right main pulmonary artery) [17, 18]. This pattern might result from per‐ sistent embryonic pulmonary‐systemic connection, as hypothesized for PDA. In these cases, a large vessel (5–8 mm diameter) is seen in middle mediastinum, emptying into the proximal part of the left or right pulmonary artery through a small orifice. A dense periesophageal

**Figure 3.** Acquired pattern of BEAH in a dog with chronic bronchopulmonary disease. A. Thin volume‐rendered image of the thorax (the head is on the right). The arrow indicates the enlarged bronchoesophageal artery. B. Arrows indicate

A *persistence of the left cranial vena cava* (CrVC) is probably the most common thoracic venous anomalies in our patients [19]. Persistent left CrVC alone is often an incidental CT finding, but may cause esophageal stenosis and may be associated with severe cardiovascular defects.

vascular network accompanies the congenital form of BEAH (**Figure 4**).

hypertrophied subsegmental bronchial arteries coursing along the corresponding bronchus.

256 Computed Tomography - Advanced Applications

Most common abdominal vascular diseases involve the caudal vena cava and the portal sys‐ tem. Caudal vena cava anomalies often have no or little clinical significance in themselves, but they are often associated with other vascular anomalies, such as portosystemic shunts that are clinically relevant [20–22]. In veterinary literature, MDCT angiographic studies are frequently reported for congenital portosystemic shunt assessment in dogs and cats [23–26]. Moreover, it is widely used also for the assessment of other pathological conditions of the portal system, such as acquired portal collaterals (APSS), portal vein aneurysm, and portal vein thrombosis [27–29]. Congenital anomalies of the abdominal segment of the descending aorta are rarely reported in small animals, and include variable pattern of renal arteries, aortic aneurism, and common celiacomesenteric trunk. Among acquired conditions, local thrombosis in the distal aorta with embolization to the iliac and/or femoral artery is the most common indication for MDCTA in dogs and cats (**Figure 5A**).

**Figure 5.** A. Aortoiliac thromboembolism in a dog with nephrotic syndrome. B. Caudal vena cava thrombosis in an oncologic patient (hepatic carcinoma).

The selection of an MDCTA scan protocol varies in consideration of the type of anomaly suspected and the vascular district (arterial, portal, or venous) potentially involved. For a comprehensive evaluation of the abdominal vascular structures, a multiphasic approach is necessary, including at least two vascular phases: arterial and portal venous phase that is also useful for the hepatic parenchyma evaluation. When CM is injected, opacification of the hepatic artery and its branches is encountered first, followed by the portal system, hepatic, and systemic veins. In veterinary literature, the peak aortic enhancement of normal dogs varies between 2 and 9.8 s, and peak enhancement of the portal vein varies between 14.6 and 46 s after contrast medium injection. Given the great diversity of patients' character‐ istics (body weight and cardiac output), the use of bolus test or automatic bolus‐triggering techniques for the individualization of scan delays in multiphasic MDCT examinations is needed.

A dual‐ or three‐phase MDCT exam can provide excellent visualization of complex vascu‐ lar anomalies and offer a comprehensive overview of the entire portal system and related parenchymal organs. Various new congenital and acquired phenotypes of portosystemic col‐ laterals have been described using MDCT technology [24–26, 30] (**Figures 6** and **7**). Good opacification of the portal venous system allows detection of endoluminal filling defects in case of portal vein thrombosis and simultaneous assessment of secondary portal collaterals (portosystemic and/or portoportal collateral vessels) (**Figure 8**).

A third vascular phase, corresponding to the interstitial hepatic phase, allows optimal visu‐ alization of systemic veins, which is essential for the evaluation of venous thrombosis and vascular invasion (**Figure 5B**). Most caudal segments of the caudal vena cava are prone to congenital variation, which is generally clinically silent themselves (**Figure 9**), but are often associated with CPSS or other vascular and nonvascular anomalies that can be of great clinical relevance.

The arterial phase is useful for detection of high‐flow vascular connections (arteriovenous fistula) at any level of the body. MCDTA images show enlarged, tortuous arteries, and premature

**Figure 6.** Extrahepatic congenital portosystemic shunt, in which the left gastric vein (LtGV) and the splenic vein had no communication with the portal vein (PV). Both veins join the anomalous vessel (PSS) that empty in the caudal vena cava (CVC). A. Dorsal thin‐MIP (maximum intensity projection) showing the end of PSS into the CVC. B. Volume‐rendered, frontal view showing the course of the PSS.

The selection of an MDCTA scan protocol varies in consideration of the type of anomaly suspected and the vascular district (arterial, portal, or venous) potentially involved. For a comprehensive evaluation of the abdominal vascular structures, a multiphasic approach is necessary, including at least two vascular phases: arterial and portal venous phase that is also useful for the hepatic parenchyma evaluation. When CM is injected, opacification of the hepatic artery and its branches is encountered first, followed by the portal system, hepatic, and systemic veins. In veterinary literature, the peak aortic enhancement of normal dogs varies between 2 and 9.8 s, and peak enhancement of the portal vein varies between 14.6 and 46 s after contrast medium injection. Given the great diversity of patients' character‐ istics (body weight and cardiac output), the use of bolus test or automatic bolus‐triggering techniques for the individualization of scan delays in multiphasic MDCT examinations is

**Figure 5.** A. Aortoiliac thromboembolism in a dog with nephrotic syndrome. B. Caudal vena cava thrombosis in an

A dual‐ or three‐phase MDCT exam can provide excellent visualization of complex vascu‐ lar anomalies and offer a comprehensive overview of the entire portal system and related parenchymal organs. Various new congenital and acquired phenotypes of portosystemic col‐ laterals have been described using MDCT technology [24–26, 30] (**Figures 6** and **7**). Good opacification of the portal venous system allows detection of endoluminal filling defects in case of portal vein thrombosis and simultaneous assessment of secondary portal collaterals

A third vascular phase, corresponding to the interstitial hepatic phase, allows optimal visu‐ alization of systemic veins, which is essential for the evaluation of venous thrombosis and vascular invasion (**Figure 5B**). Most caudal segments of the caudal vena cava are prone to congenital variation, which is generally clinically silent themselves (**Figure 9**), but are often associated with CPSS or other vascular and nonvascular anomalies that can be of great clinical

The arterial phase is useful for detection of high‐flow vascular connections (arteriovenous fistula) at any level of the body. MCDTA images show enlarged, tortuous arteries, and premature

(portosystemic and/or portoportal collateral vessels) (**Figure 8**).

needed.

oncologic patient (hepatic carcinoma).

258 Computed Tomography - Advanced Applications

relevance.

**Figure 7.** Congenital extrahepatic PSS between the left gastric vein and the right azygos vein. A. Volume‐rendered image, frontal view. Ao, aorta, Az, azygos vein. B. Volume rendered ventral view. PV, portal vein; GDV, gastroduodenal vein; SV, splenic vein; cdMV, caudal mesenteric vein. PSS, portosystemic shunt.

filling of the veins (**Figure 10**). In the liver, an early arterial phase can reveal complex hepatic arteriovenous malformations (HAVM) that are congenital anomalous connections between branches of the hepatic artery and hepatic portal vessels.

In traumatized patients, active bleeding due to arterial or venous vascular injuries can be revealed by CM extravasation in the arterial and portal venous phases. In oncology patients, a three‐phase MDCT abdominal examination provides useful information of vascular blood supply of tumors and local vascular invasion, allowing detailed interventional and surgical planning.

**Figure 8.** Portal venous phase in dogs with thrombosis of the portal system. A. The arrow indicates a filling defect in the splenic vein. B. Large arrow indicates a large filling defect in intrahepatic portal branches. The thin arrow shows some retroperitoneal varices, due to portal hypertension.

**Figure 9.** A. Dorsal MPR in a cat. The prerenal segment of the CVC is left sided (persistent left supracardinal vein and anomalous regression of the right one). B. Duplication of the prerenal segment of the CVC (partial duplication for persistent left supracardinal vein).

**Figure 10.** Peripheral arteriovenous communications in a dog. A. Volume rendering of arterial phase. Note the early enhancement of the left femoral vein. B. MIP of same volume, showing several small tortuous vessels in both legs and the muscular swelling.

### **4. Cardiac CT**

In humans, since the advent of advanced scanner technology having 64 or more detectors, the heart and coronary arteries are routinely imaged as a motion‐free volume of data. Most recent MDCT and DSCT scanners can obtain a true volumetric data set of the entire heart and adjacent structures that can be reconstructed at any point in the cardiac cycle, making CT an important imaging modality for the comprehensive assessment of cardiac morphology and function. While echocardiography remains the first‐line imaging modality, CT has become an increasingly utilized complementary imaging modality for assessment of coronary and non‐ coronary cardiac structures, including the cardiac chamber and valves, the pulmonary arteries and veins, the thoracic aorta and its proximal branches, the cardiac veins, and the pericardium.

Cardiac CT was first described in veterinary literature in 2011 for canine coronary artery assessment using a 64‐MDCT scanner [31]. Later, other studies have been published describing morphological characteristics of various cardiac structures and comparing echocardiography, magnetic resonance (MR) and CT measurements [32, 33]. As for humans, cardiac CT in veteri‐ nary patients has now become an increasingly utilized modality for the assessment of cardiac congenital conditions, cardiac and paracardiac masses, and pericardial diseases [34–36]. In clinical practice, morphological evaluation of these conditions is generally performed with non‐ECG‐gated CT protocols, as a part of a thoracic CT examination. Most recent MDCT is not only fast but also has high spatial and temporal resolutions, multiplanar reconstruction (MPR) capabilities, and a wide field of view, which provides information of the heart, mediastinum, and adjacent structures, including the lungs. A non‐ECG‐gated CT examination, however, is not a reliable way for comprehensive evaluation of small cardiac structures (e.g., coronary arteries and valves), congenital heart diseases, cardiac sizes and in many other clinical situa‐ tions using first generation of MDCT scanners (≤64 rows) [32, 33]. With most advanced MDCT scanners (e.g., 128–320 detector rows) and DSCT technology, it is possible to obtain high‐reso‐ lution, submillimetric data in a few seconds, providing excellent morphological detail of the heart and paracardiac structures, having minimal or no motion artifacts. For instance, at our center, now equipped with a second generation of dual‐source 128‐slice CT systems, cardio‐ thoracic CT examination can be performed at a high‐pitch, up to 3.4 with gantry rotation time of 0.28 s and a temporal resolution of 75 ms (**Figure 11**).

### **4.1. Cardiac CT basic principles**

**Figure 10.** Peripheral arteriovenous communications in a dog. A. Volume rendering of arterial phase. Note the early enhancement of the left femoral vein. B. MIP of same volume, showing several small tortuous vessels in both legs and

**Figure 8.** Portal venous phase in dogs with thrombosis of the portal system. A. The arrow indicates a filling defect in the splenic vein. B. Large arrow indicates a large filling defect in intrahepatic portal branches. The thin arrow shows some

**Figure 9.** A. Dorsal MPR in a cat. The prerenal segment of the CVC is left sided (persistent left supracardinal vein and anomalous regression of the right one). B. Duplication of the prerenal segment of the CVC (partial duplication for

retroperitoneal varices, due to portal hypertension.

260 Computed Tomography - Advanced Applications

the muscular swelling.

persistent left supracardinal vein).

For motion‐free and of diagnostic value imaging of the heart, high temporal and spatial resolu‐ tion are both essential, especially in veterinary patients who have variable heart rates. CT data should be assessed during certain phases of the cardiac cycle with little cardiac motion. Ideally, a complete data set of the whole heart would be acquired within a single phase of the cardiac cycle without movement. Two methods are possible for virtually freezing the heart: prospective gating with sequential or step‐and‐shoot scanning mode and retrospective ECG gating (spiral) [37, 38].

In *prospective ECG‐triggered sequential CT‐scanning* using partial‐scan technique, the scan is syn‐ chronized to the motion of the heart in order to acquire data preferably in the diastolic phase, when cardiac motion is minimal. After every scan, the table moves by the width of the acquired scan range in the *z*‐direction toward the next scan position in order to provide gap‐less volume

**Figure 11.** Non‐ECG‐gated, high‐pitch 128‐DSCT (Flash mode) of the thorax in a dog with pulmonary embolism. A transverse view. Arrows show the filling defects in pulmonary vessels, due to thrombosis. Cardiac structures are "freezed" (lv, left ventricle).

coverage (step‐and‐shot). The delay time for scan acquisition after an R‐wave is individually based on a prospective estimation of the R‐R intervals, attempting to acquire the data during the diastolic phase of the heart. Using this technique, small changes in heart rate during the sequential scan can cause acquisition in inconsistent heart phases and thus inconsistent volume coverage, resulting in artifacts at the intersections of adjacent image stacks and subsequent misregistration of lesions along *z‐*axis. This may represent a limitation especially for veterinary patients, where many cardiac structures are small and complex 3D structures that require the highest possible image quality. Moreover, with prospective ECG triggering, estimation of the next R‐R interval may be incorrect when heart‐rate changes are present, such as in patients with arrhythmia or with a single premature ventricular contraction, which makes sections of the heart entirely uninterpretable.

In *retrospectively ECG‐gated spiral scanning,* reconstructions of a continuous spiral scan are synchronized to the movement of the heart by using an ECG trace that is recorded simulta‐ neously. The great advantage of retrospectively ECG‐gated MDCT‐spiral scanning is that it provides an isotropic, 3D image data set of the complete cardiac volume without gaps and misregistration of data. Retrospective ECG gating data are available during all phases of the cardiac cycle and this offers the possibility of retrospectively modifying the synchronization of the ECG trace and data reconstruction, choosing the best R‐R interval for image analysis. Individual adjustment of the image‐interval‐position is extremely useful for imaging those patients with fast and irregular heart rate.

The scanner technology available greatly influences the scan protocol for cardiac CT evalu‐ ation. The maximum pitch in single source MDCT is usually about 1.5. Last generation of DSCT scanners allow pitch value up to 3.4. This results in maximum scan speed of 737 mm/s, which allows continuous volume coverage of a whole body in one second or less with iso‐ tropic resolution [38]. Since this impressive temporal resolution, pharmacological pretreat‐ ment for heart rate modulation is not necessary in our patients. High‐detailed images of the heart can be obtained also in awake patients, independently on the heart rate. However, using this approach, cardiac function evaluation is not possible. In our experience, low‐pitch retro‐ spective ECG‐gated 128‐DSCT cardiac examination performed without any pharmacological pretreatment to reduce patient's heart rate provides excellent images, useful either for mor‐ phological or functional assessments.

Factors influencing the CM hemodynamic distribution are similar to those described before for CTA. CM injection protocol should take into account the body weight and cardiac out‐ put of the patient. Both the bolus test and the bolus‐triggering techniques can be used for CM injection individualization for cardiac evaluation. In standard cardiac CT for coronary artery evaluation, the ROI is placed in the ascending aorta. In this approach, the left ventricu‐ lar and left atrial walls and cavities, as well as left‐sided valves, will be uniformly opacified (**Figures 12** and **13**). However, depending on the contrast agent infusion protocol, the right‐sided

**Figure 12.** Retrospective ECG‐gated cardiac examination with 128‐DSCT (low pitch). Note the absence of motion artifacts (the patient was under general anesthesia, mechanically ventilated). The ROI has been placed on the ascending aorta (standard cardiac CT). Note the great enhancement of the aorta, left atrium, and ventricle.

**Figure 13.** Retrospective ECG‐gated cardiac CT in a dog (128‐DSCT).

coverage (step‐and‐shot). The delay time for scan acquisition after an R‐wave is individually based on a prospective estimation of the R‐R intervals, attempting to acquire the data during the diastolic phase of the heart. Using this technique, small changes in heart rate during the sequential scan can cause acquisition in inconsistent heart phases and thus inconsistent volume coverage, resulting in artifacts at the intersections of adjacent image stacks and subsequent misregistration of lesions along *z‐*axis. This may represent a limitation especially for veterinary patients, where many cardiac structures are small and complex 3D structures that require the highest possible image quality. Moreover, with prospective ECG triggering, estimation of the next R‐R interval may be incorrect when heart‐rate changes are present, such as in patients with arrhythmia or with a single premature ventricular contraction, which makes sections of

**Figure 11.** Non‐ECG‐gated, high‐pitch 128‐DSCT (Flash mode) of the thorax in a dog with pulmonary embolism. A transverse view. Arrows show the filling defects in pulmonary vessels, due to thrombosis. Cardiac structures are

In *retrospectively ECG‐gated spiral scanning,* reconstructions of a continuous spiral scan are synchronized to the movement of the heart by using an ECG trace that is recorded simulta‐ neously. The great advantage of retrospectively ECG‐gated MDCT‐spiral scanning is that it provides an isotropic, 3D image data set of the complete cardiac volume without gaps and misregistration of data. Retrospective ECG gating data are available during all phases of the cardiac cycle and this offers the possibility of retrospectively modifying the synchronization of the ECG trace and data reconstruction, choosing the best R‐R interval for image analysis. Individual adjustment of the image‐interval‐position is extremely useful for imaging those

The scanner technology available greatly influences the scan protocol for cardiac CT evalu‐ ation. The maximum pitch in single source MDCT is usually about 1.5. Last generation of DSCT scanners allow pitch value up to 3.4. This results in maximum scan speed of 737 mm/s, which allows continuous volume coverage of a whole body in one second or less with iso‐ tropic resolution [38]. Since this impressive temporal resolution, pharmacological pretreat‐ ment for heart rate modulation is not necessary in our patients. High‐detailed images of the heart can be obtained also in awake patients, independently on the heart rate. However, using

the heart entirely uninterpretable.

"freezed" (lv, left ventricle).

262 Computed Tomography - Advanced Applications

patients with fast and irregular heart rate.

chambers, walls, and valves may or may not be suitable for interpretation. Optimal timing for right heart good opacification can be achieved placing the ROI for test bolus or bolus track‐ ing in the main pulmonary artery. Achievement of diagnostically adequate homogeneous enhancement of the right atrium can be difficult because of mixing of unopacified blood from the caudal vena cava with high‐attenuating contrast agent‐opacified blood from the cranial vena cava. Streak artifacts due to high concentration of CM in the cranial vena cava or right atrium may obscure some structures or simulate the presence of masses or thrombotic lesions. Dual or triple CM bolus injection technique may lead to a more uniform opacification of right‐ sided cardiac structures. This may be necessary for the evaluation of patients with certain congenital heart diseases or cardiac masses.

#### **4.2. Cardiac CT clinical applications**

With ECG‐gated cardiac CT examination, the anatomy of the heart is clearly depicted. MDCT is the preferred imaging modality when anomalous origin and course of coronary arteries is suspected [32, 39] (**Figure 14**). Compared to human literature, reports of congenital artery anomalies in animals are sparse, presumably because coronary artery disease is less common in veterinary patients and rarely of clinical significance, unless in the setting of pulmonary valve stenosis (PS). Further, advanced diagnostic imaging of the heart is not routinely per‐ formed, thus underestimating the frequency of coronary anomalies in our patients. ECG‐ gated cardiac CT allows the simultaneous evaluation of other noncoronary structures of the heart. Left and right chambers are well defined from the cardiac muscular wall and from interventricular and interatrial septum. Small structures, such as atrioventricular valves, aor‐ tic and pulmonary valves, papillary muscles of both ventricles, and trabeculae carneae are easily distinguishable [31].

**Figure 14.** Retrospective ECG‐gated cardiac CT in a dog with anomalous right origin of septal coronary artery branch (128‐DSCT).

Using retrospective ECG‐gated mode with full cardiac cycle available, functional evaluations of the heart are also possible. In postprocessing, multiplanar analysis (MPR) of volume data‐ set allows standard planar and volumetric measurements, using same image planes normally used in echocardiography [32–35]. ECG‐gated cardiac CT is also useful in patients with con‐ genital cardiac defects such as PDA, PS, or more complex congenital heart diseases. Moreover, it is helpful for planning surgical and interventional procedures [16, 40] (**Figures 15**, **16**).

chambers, walls, and valves may or may not be suitable for interpretation. Optimal timing for right heart good opacification can be achieved placing the ROI for test bolus or bolus track‐ ing in the main pulmonary artery. Achievement of diagnostically adequate homogeneous enhancement of the right atrium can be difficult because of mixing of unopacified blood from the caudal vena cava with high‐attenuating contrast agent‐opacified blood from the cranial vena cava. Streak artifacts due to high concentration of CM in the cranial vena cava or right atrium may obscure some structures or simulate the presence of masses or thrombotic lesions. Dual or triple CM bolus injection technique may lead to a more uniform opacification of right‐ sided cardiac structures. This may be necessary for the evaluation of patients with certain

With ECG‐gated cardiac CT examination, the anatomy of the heart is clearly depicted. MDCT is the preferred imaging modality when anomalous origin and course of coronary arteries is suspected [32, 39] (**Figure 14**). Compared to human literature, reports of congenital artery anomalies in animals are sparse, presumably because coronary artery disease is less common in veterinary patients and rarely of clinical significance, unless in the setting of pulmonary valve stenosis (PS). Further, advanced diagnostic imaging of the heart is not routinely per‐ formed, thus underestimating the frequency of coronary anomalies in our patients. ECG‐ gated cardiac CT allows the simultaneous evaluation of other noncoronary structures of the heart. Left and right chambers are well defined from the cardiac muscular wall and from interventricular and interatrial septum. Small structures, such as atrioventricular valves, aor‐ tic and pulmonary valves, papillary muscles of both ventricles, and trabeculae carneae are

**Figure 14.** Retrospective ECG‐gated cardiac CT in a dog with anomalous right origin of septal coronary artery branch

congenital heart diseases or cardiac masses.

**4.2. Cardiac CT clinical applications**

264 Computed Tomography - Advanced Applications

easily distinguishable [31].

(128‐DSCT).

**Figure 15.** 128‐DSCT, ECG‐gated cardio CT in PDA in a dog (pre‐interventional assessment) and corrected PDA with Amplatzer duct occluder (VR on the right).

**Figure 16.** Retrospective ECG‐gated cardiac 128‐DSCT in dogs with pulmonic stenosis. A. Images on the left have been automatically reconstructed by the software in best‐systolic phase and those on the right in best diastole (less motion artifacts). B. VR of another dog with pulmonic stenosis and post stenotic bulge of right ventricular outflow tract.

**Figure 17.** ECG‐gated cardiothoracic examination (128‐DSCT) in a dog with heart‐base tumor (mass).

In clinical practice, primary or metastatic cardiac tumors can be easily identified during routine non‐ECG‐gated examination of the thorax. However, ECG‐gated cardiac imaging in patients with suspected or known cardiac‐paracardiac or pericardial tumors minimizes motion‐related artifacts and allows a more precise delineation of the lesion margins (**Figure 17**).

### **Author details**

Giovanna Bertolini\* and Luca Angeloni

\*Address all correspondence to: bertolini@sanmarcovet.it

Diagnostic and Interventional Radiology Division, San Marco Veterinary Clinic, Padova, Italy

### **References**


In clinical practice, primary or metastatic cardiac tumors can be easily identified during routine non‐ECG‐gated examination of the thorax. However, ECG‐gated cardiac imaging in patients with suspected or known cardiac‐paracardiac or pericardial tumors minimizes motion‐related

Diagnostic and Interventional Radiology Division, San Marco Veterinary Clinic, Padova, Italy

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artifacts and allows a more precise delineation of the lesion margins (**Figure 17**).

**Figure 17.** ECG‐gated cardiothoracic examination (128‐DSCT) in a dog with heart‐base tumor (mass).

**Author details**

**References**

Giovanna Bertolini\* and Luca Angeloni

266 Computed Tomography - Advanced Applications

\*Address all correspondence to: bertolini@sanmarcovet.it


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268 Computed Tomography - Advanced Applications


## **Computed Tomography in Veterinary Medicine: Currently Published and Tomorrow's Vision**

Matthew Keane, Emily Paul, Craig J Sturrock, Cyril Rauch and Catrin Sian Rutland

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68556

#### **Abstract**

The utilisation of computed tomography (CT) in veterinary practise has been increasing rapidly in line with reduced cost, improved availability and the increase in expertise and technology. This review briefly examines the recent technological advancements in imaging in the veterinary sector, and explores how CT and micro-computed tomography (μCT) have furthered basic understanding and knowledge, and influenced clinical practise and medicine. The uses of CT technology in veterinary research, especially in relation to bone, vasculature and soft tissues are explored and compared in relation to the different species. CT is essential not only for the diagnosis and treatment of many disorders, but it is now being used to understand areas ranging from drug delivery and surgical advancements through to anatomical and educational uses throughout the world.

**Keywords:** veterinary, computed tomography, clinical, research, bone, vasculature

### **1. Overview of computed tomography in veterinary medicine**

The introduction of computed tomography (CT) has provided one of the most important advancements in diagnostic imaging in the veterinary sector. In contrast to standard diagnostic radiography, CT produces an axial slice of the area under investigation and a resultant three-dimensional image. CT also allows greater differentiation between individual soft tissue structures than diagnostic radiography. This is due to the ability of CT to accurately measure the tissue absorption of X-ray beams as they pass through the patient [1].

Since the inception of CT, the technology has been developed to yield further improvements. The original first generation of CT scanners consisted of a single detector and an X-ray tube

which produced a single narrow beam. The assembly of X-ray and detector linearly scanned the whole patient in the axial plane. Together, the X-ray beam and detector are rotated by 1° after each single line image. At the end of the process, each individual scan was then compiled to produce an image in a process known as reconstruction [1].

A pitfall of the first generation of CT scanners was the time taken to acquire an image, with a single slice taking up to 6 min [2]. The development of second generation CT scanners aimed to address this with the introduction of an X-ray tube which produced several narrow beams and generated a fan-shaped projection. The fan-shaped beam was directed at multiple detectors and together this system would rotate as a unit around 360° to generate an image. As fewer incremental steps were required whilst scanning the whole patient, this resulted in shorter scan times of up to 20 s for each slice [3, 4]. But even with this marked improvement in time taken to generate each slice, image quality was still affected by artefacts associated with the technology and movement blur [2, 5].

Further advancements of the technology resulted in third and fourth generation scanners which could acquire individual image slices considerable faster at a rate of one image per second from a patient. Third generation scanners consisted of an X-ray beam which spanned the entire width of the patient which was directed at an assembly of detectors. Both the X-ray tube and the assembly of detectors rotate 360° around the patient on a fixed frame (gantry) to produce a movement known as rotation-rotation. Fourth generation CT scanners are composed of an X-ray tube which rotates around the patient and directs its beam at a ring of fixed stationary detectors built into the machine housing [6].

### **2. Clinical uses of computed tomography in veterinary medicine**

The use of CT in veterinary medicine in a clinical setting was first documented in the 1980s for the investigation of disease of the central nervous system and neoplasia in canines [7–10]. CT has become more common in veterinary medicine due to the technological advancements of CT and its increased availability in general practise. Another imaging modality which is becoming increasingly available in the veterinary sector is magnetic resonance imaging (MRI). The use of MRI is most commonly indicated in conditions that require differentiation between soft tissues, such as in the field of neurology, whereas CT is useful for imaging both bones and soft tissues [11].

In small animals, the use of CT is most commonly indicated in patients with thoracic and abdominal disease, intracranial and extracranial lesions, and disorders of the musculoskeletal system including the appendicular skeleton and spine [12–17]. As the generation of images in CT is so rapid, this diagnostic modality is important in cases where anaesthesia and sedation are not an option. CT is therefore useful in emergency critical cases or disorders which may be compromised by anaesthesia or sedation [18, 19].

In equine veterinary medicine, the use of CT is most appropriate in the assessment of structures with mixed tissue thickness and thus differing levels of tissue absorption of X-rays. Therefore, the structures most commonly assessed are the appendicular skeleton for diagnostic lameness work-ups, the dental arcade, paranasal sinuses and the skull [20–28]. In the clinic, patient positioning provides complications due to the size of the horse, although a hovercraft-design table alongside horse sedation (a technique revolutionised by the late Alastair Nelson) has enabled considerable development of scans involving the head [29].

which produced a single narrow beam. The assembly of X-ray and detector linearly scanned the whole patient in the axial plane. Together, the X-ray beam and detector are rotated by 1° after each single line image. At the end of the process, each individual scan was then compiled

A pitfall of the first generation of CT scanners was the time taken to acquire an image, with a single slice taking up to 6 min [2]. The development of second generation CT scanners aimed to address this with the introduction of an X-ray tube which produced several narrow beams and generated a fan-shaped projection. The fan-shaped beam was directed at multiple detectors and together this system would rotate as a unit around 360° to generate an image. As fewer incremental steps were required whilst scanning the whole patient, this resulted in shorter scan times of up to 20 s for each slice [3, 4]. But even with this marked improvement in time taken to generate each slice, image quality was still affected by artefacts associated with

Further advancements of the technology resulted in third and fourth generation scanners which could acquire individual image slices considerable faster at a rate of one image per second from a patient. Third generation scanners consisted of an X-ray beam which spanned the entire width of the patient which was directed at an assembly of detectors. Both the X-ray tube and the assembly of detectors rotate 360° around the patient on a fixed frame (gantry) to produce a movement known as rotation-rotation. Fourth generation CT scanners are composed of an X-ray tube which rotates around the patient and directs its beam at a ring of

The use of CT in veterinary medicine in a clinical setting was first documented in the 1980s for the investigation of disease of the central nervous system and neoplasia in canines [7–10]. CT has become more common in veterinary medicine due to the technological advancements of CT and its increased availability in general practise. Another imaging modality which is becoming increasingly available in the veterinary sector is magnetic resonance imaging (MRI). The use of MRI is most commonly indicated in conditions that require differentiation between soft tissues, such as in the field of neurology, whereas CT is useful for imaging both

In small animals, the use of CT is most commonly indicated in patients with thoracic and abdominal disease, intracranial and extracranial lesions, and disorders of the musculoskeletal system including the appendicular skeleton and spine [12–17]. As the generation of images in CT is so rapid, this diagnostic modality is important in cases where anaesthesia and sedation are not an option. CT is therefore useful in emergency critical cases or disorders which may

In equine veterinary medicine, the use of CT is most appropriate in the assessment of structures with mixed tissue thickness and thus differing levels of tissue absorption of X-rays. Therefore,

to produce an image in a process known as reconstruction [1].

fixed stationary detectors built into the machine housing [6].

be compromised by anaesthesia or sedation [18, 19].

**2. Clinical uses of computed tomography in veterinary medicine**

the technology and movement blur [2, 5].

272 Computed Tomography - Advanced Applications

bones and soft tissues [11].

The application of CT in a clinical setting to produce diagnostic images in cattle is not common. CT is often reserved for valuable cattle, primarily due to its expense but also due to the use of general anaesthetics and off-label drugs [30]. Unlike small animal and equine imaging, it is not often used for the appendicular skeleton or spine. The most common indications for its use are disease of the central nervous system, otitis media and dental disease.

### **3. The technical use of micro-computed tomography (μCT) in veterinary medicine and research**

Recent technological advances are rendering the use of CT imaging as a diagnostic technique and preoperative tool increasingly common in veterinary medicine. These technological advances have, similarly, opened new possibilities in the field of research, which include the investigation of both hard and soft tissues, at and below the micrometre scale, providing physiological information non-destructively on the sample [31].

X-ray imaging is based around the principle of attenuation—the reduction of signal as the photons interact with electrons in the matter, known as the absorber, through which they are being passed [31]. The linear attenuation coefficient (*μ*), defined as the proportion of incident photon intensity reduction per unit length of absorber and expressed in cm−1, is dictated by photon energy (*E*) and atomic number (*Z*). Photon intensity (*I*) decreases exponentially as a function of absorber thickness (*t*) in a homogenous absorber, as shown in the equation below [32, 33].

$$l = l\_o \exp\left(-\mu t\right) \tag{1}$$

*I0* is the incident radiation intensity, *μ =* linear attenuation coefficient, *I* = photon intensity, *t* = absorber thickness.

Attenuation principally arises from two processes: Compton scattering and photoelectric absorption [32]. Compton scattering involves the transfer of a proportion of the energy of the incident photon to an electron, resulting in the emission of a lower energy photon [34], and photoelectric absorption is the complete transfer of the incident photon energy [35]. Compton scattering is determined principally by *Z*, with the effect of *E* being only minimal, while photoelectric absorption is strongly dependent on both [32]. The attenuation of biological soft tissues, which display relative uniformity in their low-*Z* constituents [31], and bones is predominantly in the form of photoelectric absorption at low energy ranges (*E* = 30–50 keV) and Compton scattering and at higher energy levels (*E* = 200–1000 keV). With *E* ranging from 30 to 130 keV in X-ray radiographic imaging, attenuation in CT imaging usually results from a combination of photoelectric absorption and Compton scattering [32]. As CT detectors are not energy-discriminative and solely detect *I*, greater contrast is achieved at lower *E* levels where photoelectric absorption prevails [31, 32].

The X-rays used in μCT imaging may come from a laboratory X-ray generator or a synchrotron source. Synchrotron-source X-rays tend to be used monochromatically, with an *E* selected from a range, while laboratory-generated X-ray beams usually consist of peaks of characteristic X-rays with white (polychromatic) beams from breaking radiation (bremsstrahlung radiation). Thus voxel (volumetric pixel) values directly represent *μ* in synchrotron but not in laboratory CT [31].

### **4. Clinical and research investigations into bone tissue**

CT has been used to investigate a number of bone and growth disorders. The key to CT scanning is that it can be used to visualise not only gross anatomy, such as fractures and general morphology, but can also show micro fractures, bone thickness, trabecular bone distortion and architecture, and bone curvature and angles in situ. When the variety of functions that can be applied to the normal body is considered, the uses for CT and μCT in diseases, disorders and in other studies are wide ranging. Cortical bone thickness and trabecular bone distortion can be used as indicators of localised mechanical strain [36] and it is likely that it is linked to many bone disorders in addition to fractures and trauma incidents.

Normal growth and development can be observed using CT scanning. As part of a study into human trabecular bone ontogeny, the femur trabecular number, thickness, and bone volume fraction were investigated from the foetus and youths up to 9 years of age [37]. These studies showed an increase in trabecular bone thickness and bone volume fraction, but a decrease in trabecular number at around a year old, coinciding with the onset of unaided walking and, as a consequence, load bearing was concluded to be causal of the changes observed. Similar observations have also been noted in nonhuman animals. An example is shown in the cat, where bone material density was used in the diagnosis of osteopenia and in order to quantify the benefits of the applied treatments [38]. μCT has shown the effectiveness of titanium lattice implants in relation to bone ingrowth and bone contact in rat, which has implications for not only veterinary but also human medicine [39]. Results from guinea pig have shown how bone research can help identify differences in bone development and structure. Despite adult weight being achieved at around 9–12 months of age, the study showed that bone development continued beyond 12 months [40]. The authors were also able to give detailed anatomical descriptions of the bones, show where weaker areas might occur, (which is useful in understanding fractures) and show that differing bones had different growth rates. Examples of the high quality of images and cortical bone thickness are shown in **Figure 1**. Using CT measurements has been shown to be more accurate than callipers in humans [41] and although the guinea pig study showed no significant differences between the two methods, the largest variation was observed within the smallest bones [40] indicating that for smaller measurements CT may be more applicable but more research needs to be undertaken in this area in differing measurement sizes to understand the limitations of each technique.

Computed Tomography in Veterinary Medicine: Currently Published and Tomorrow's Vision http://dx.doi.org/10.5772/intechopen.68556 275

combination of photoelectric absorption and Compton scattering [32]. As CT detectors are not energy-discriminative and solely detect *I*, greater contrast is achieved at lower *E* levels where

The X-rays used in μCT imaging may come from a laboratory X-ray generator or a synchrotron source. Synchrotron-source X-rays tend to be used monochromatically, with an *E* selected from a range, while laboratory-generated X-ray beams usually consist of peaks of characteristic X-rays with white (polychromatic) beams from breaking radiation (bremsstrahlung radiation). Thus voxel (volumetric pixel) values directly represent *μ* in synchrotron but not in laboratory CT [31].

CT has been used to investigate a number of bone and growth disorders. The key to CT scanning is that it can be used to visualise not only gross anatomy, such as fractures and general morphology, but can also show micro fractures, bone thickness, trabecular bone distortion and architecture, and bone curvature and angles in situ. When the variety of functions that can be applied to the normal body is considered, the uses for CT and μCT in diseases, disorders and in other studies are wide ranging. Cortical bone thickness and trabecular bone distortion can be used as indicators of localised mechanical strain [36] and it is likely that it is linked to many bone disorders in addition to fractures and trauma incidents. Normal growth and development can be observed using CT scanning. As part of a study into human trabecular bone ontogeny, the femur trabecular number, thickness, and bone volume fraction were investigated from the foetus and youths up to 9 years of age [37]. These studies showed an increase in trabecular bone thickness and bone volume fraction, but a decrease in trabecular number at around a year old, coinciding with the onset of unaided walking and, as a consequence, load bearing was concluded to be causal of the changes observed. Similar observations have also been noted in nonhuman animals. An example is shown in the cat, where bone material density was used in the diagnosis of osteopenia and in order to quantify the benefits of the applied treatments [38]. μCT has shown the effectiveness of titanium lattice implants in relation to bone ingrowth and bone contact in rat, which has implications for not only veterinary but also human medicine [39]. Results from guinea pig have shown how bone research can help identify differences in bone development and structure. Despite adult weight being achieved at around 9–12 months of age, the study showed that bone development continued beyond 12 months [40]. The authors were also able to give detailed anatomical descriptions of the bones, show where weaker areas might occur, (which is useful in understanding fractures) and show that differing bones had different growth rates. Examples of the high quality of images and cortical bone thickness are shown in **Figure 1**. Using CT measurements has been shown to be more accurate than callipers in humans [41] and although the guinea pig study showed no significant differences between the two methods, the largest variation was observed within the smallest bones [40] indicating that for smaller measurements CT may be more applicable but more research needs to be undertaken in this area in differing measurement sizes to understand the limitations of each technique.

**4. Clinical and research investigations into bone tissue**

photoelectric absorption prevails [31, 32].

274 Computed Tomography - Advanced Applications

**Figure 1.** 3D rendered 4-year old guinea pig bones showing surface morphology (A, C, E) and cortical bone thickness (B, D, F) of the humerus (A, D), femur (B, E) and scapula (C, F). Bone thickness was mapped, where increasing brightness indicates thicker bone. BoneJ plugin for ImageJ [42] was utilised to calculate bone thickness.

CT for the assessment of equine disorders such as complex foot lameness cases is expanding [20]. Recent studies have shown visible thinning and fractures within bones of chronically laminitic horses, using μCT and histopathology in parallel [43]. μCT studies have also given enormous insights into bovine lameness. By combining clinical data with μCT images and measurements, direct correlations between bone damage, remodelling and growth were made, thus giving new insights into the mechanisms behind bovine lameness [44]. In addition to visualising bone measurements such as thickness, trabeculation and anatomical size, CT is an excellent platform for understanding bone angle and rotation, useful in understand deformities, dysplasia, neoplasia, osteopathies and degenerative diseases in addition to normal anatomy or in trauma situations. A good example of monitoring bone angles is some of the early imaging of the canine and feline temporomandibular joint, as this joint is particularly difficult to visualise using traditional radiographic techniques [45], and its use during/postsurgery to assess bone angle and healing, particularly in companion animals such as cats and dogs [46, 47].

CT is not restricted to small animal analysis and diagnosis. Although an elephant may be difficult to scan whilst alive, post-mortem tissue gives valuable insights into pathologies. An example was the work carried out into elephant foot pathology and anatomy. In this species, foot problems cause a substantial number of morbidity and mortality issues, and work undertaken to understand these showed a range of complications, from bone remodelling through to osteoarthritis and fractures [48]. Similar work has also been carried out in the rhinoceros [49]. Comparisons between elephants of differing ages, sexes and species (African vs. Asian) were made and, although captive (zoo) animals were used [48], there is potential for assessing and comparing wild animals in the future. Studies such as these can have beneficial outcomes on the way that animals are managed in captivity. Understanding what may influence disease and cause damage can help provide management mechanisms, thus enhancing animal health and welfare.

As a physiologically active tissue, bone's high adaptability to its environment can provide insight into the pathophysiological status of its surroundings [50]. While the osseous remodelling processes may be induced through a number of mechanisms such as trauma, ageing and disease, CT imaging can provide valuable insights into the bone's adaptive capabilities in terms of gross shape, cortical thickness, trabecular anisotropy and position within the body and in relation to other structures.

### **5. Clinical and research investigations into soft tissues**

Visualising soft tissue and achieving contrast between the differing tissues can be a challenge [31]. Due to these difficulties there are numerous uses and techniques being developed in order to investigate soft tissue and liquids using CT. A separate section on vasculature CT is given below (Section 6).

The current method of staging canine appendicular osteosarcoma relies on radiography alongside scintigraphy, however work is being undertaken to try to use CT as an alternative. One such study showed that CT could effectively show malignancies in the thorax and abdomen, and lung lesions but it had a lower detection of appendicular osteosarcoma than the present methods [51]. It was suggested that diagnosis may be reduced due to reader fatigue, as shown in human radiology, but that slice thickness and lesion size may also play important roles. More development is needed in this area before CT can be used as a standalone tool for diagnosis. In other tumour types, CT is more successful. In the case of canine thyroid tumours, CT is recommended for both preoperative diagnosis and for staging [52, 53]. It has also been recommended that any middle aged dog that has a body CT should be checked for incidental thyroid nodules as, although rare, they are identifiable [54]. CT is already regularly used for staging cancers, and each tumour type must be individually assessed as to which method is most appropriate for this vital process. Significant improvements in dogs with nasal neoplasia are observed when CT is utilised to stage tumours [55] and whereas the World Health Organisation staging guidance was originally based around radiography, this has since been updated to include CT [56, 57].

use during/postsurgery to assess bone angle and healing, particularly in companion animals

CT is not restricted to small animal analysis and diagnosis. Although an elephant may be difficult to scan whilst alive, post-mortem tissue gives valuable insights into pathologies. An example was the work carried out into elephant foot pathology and anatomy. In this species, foot problems cause a substantial number of morbidity and mortality issues, and work undertaken to understand these showed a range of complications, from bone remodelling through to osteoarthritis and fractures [48]. Similar work has also been carried out in the rhinoceros [49]. Comparisons between elephants of differing ages, sexes and species (African vs. Asian) were made and, although captive (zoo) animals were used [48], there is potential for assessing and comparing wild animals in the future. Studies such as these can have beneficial outcomes on the way that animals are managed in captivity. Understanding what may influence disease and cause damage can help provide management mechanisms, thus enhancing animal health

As a physiologically active tissue, bone's high adaptability to its environment can provide insight into the pathophysiological status of its surroundings [50]. While the osseous remodelling processes may be induced through a number of mechanisms such as trauma, ageing and disease, CT imaging can provide valuable insights into the bone's adaptive capabilities in terms of gross shape, cortical thickness, trabecular anisotropy and position within the body

Visualising soft tissue and achieving contrast between the differing tissues can be a challenge [31]. Due to these difficulties there are numerous uses and techniques being developed in order to investigate soft tissue and liquids using CT. A separate section on vasculature CT

The current method of staging canine appendicular osteosarcoma relies on radiography alongside scintigraphy, however work is being undertaken to try to use CT as an alternative. One such study showed that CT could effectively show malignancies in the thorax and abdomen, and lung lesions but it had a lower detection of appendicular osteosarcoma than the present methods [51]. It was suggested that diagnosis may be reduced due to reader fatigue, as shown in human radiology, but that slice thickness and lesion size may also play important roles. More development is needed in this area before CT can be used as a standalone tool for diagnosis. In other tumour types, CT is more successful. In the case of canine thyroid tumours, CT is recommended for both preoperative diagnosis and for staging [52, 53]. It has also been recommended that any middle aged dog that has a body CT should be checked for incidental thyroid nodules as, although rare, they are identifiable [54]. CT is already regularly used for staging cancers, and each tumour type must be individually assessed as to which method is most appropriate for this vital process.

**5. Clinical and research investigations into soft tissues**

such as cats and dogs [46, 47].

276 Computed Tomography - Advanced Applications

and in relation to other structures.

is given below (Section 6).

and welfare.

CT can reduce the number of surgical procedures undertaken or enable keyhole surgeries. Thoracic duct lymphography has been undertaken under research conditions and in canine patients with chylothorax, using CT and iodine as a contrasting agent. Furthermore, the technique was demonstrated to be beneficial when used post-surgery to check for recurrence [58, 59] as it was described as minimally invasive and easy to perform. A similar technique was used to look at feline lymphography. CT was able to show the small mammary lymphatic vessels and lymph nodes with minimal side effects [60].

CT has shown considerable promise for study of lesions such as cysts, abscesses, hydrocephalus and coenurosis lesions in ruminants, including sheep, cattle and the alpaca [61–64]. Ruminant brain disorders and malformations have been observed [61, 65]. These are increasingly used as the lower cost and reduced anaesthesia required in comparison to MRI is seen as favourable, especially in small ruminants and calves [66]. CT is presently used for assessing muscle mass, and is considered as the 'gold standard' alongside MRI. The technique is able to successfully differentiate between differing soft tissues such as skin and muscle. Muscle mass is critical in a number of situations including injury, chronic wasting, malnourishment, and during hospital and rest phases. In an interesting study, urine was examined rather than soft tissues. CT was used in a non-invasive manner to gauge whether urine concentration could be assessed in canine patients undergoing abdominal imaging [67]. The work even showed that the X-ray attenuation of urine could be measured. This has significant implications not only for measuring urine in differing species, but holds the potential for measuring other types of biological fluids.

Echocardiograms are frequently used for cardiovascular disorders, but CT is increasingly being utilised in research and in the clinical setting. One of the attractions of using CT is that second or third generation dual source scanner can scan animals at high speed and therefore within a heartbeat—if the heart is not beating too quickly [68]. Frequently CT is used to locate physical deformities such as atrial and ventricular septal defects, following device placement and surgery. It can also be used to look at general heart morphology and development in models of disease, and in animals with abnormalities such as endocarditis and regurgitation, to look at narrowing of the blood vessels such as the aorta, and to look for occlusions, seromas and abscesses [69].

### **6. Clinical and research investigations into vasculature**

Vascular disturbances have long been associated to the pathologenesis of differing disorders [70], and digital venography is a commonly employed technique providing vital information for treatment options and for monitoring their progress [71]. CT images provide higher levels of quantitative information than venograms, enabling the visualisation of discrete areas rather than an overall impression of perfusion rate based on X-ray attenuation of contrast agents in numerous vessels simultaneously. Naturally, in the case of μCT, the post-mortem nature of the samples renders speculation on vasoactivity impossible, but this technique can still provide insights into vascularisation.

A number of different functions can now be investigated in relation to vasculature using CT. Complex 3D models of whole or partial organism vasculature can show areas of angiogenesis and neovascularisation. This technique can also show network interactions, show where vascular junctions and branching occurs, and indicate lumen diameter within a given area. There is an added complexity with blood vessels in that once blood flow ceases, the vascular morphology is altered. In order to preserve the tissues and permit a good visibility of the vasculature once scanned, tissues can be perfused and fixed while fresh. The aim of fixation is to maintain tissues in a life-like state, and perfusion fixation provides the optimal route for the fixative to reach the tissues upon which it can quickly act [72], while fixing the blood vessels in such a way to prevent their collapse and allow them to fill with air, providing the contrast between vessel lumen and the surrounding tissues. Achieving a balance in contrast between soft tissues, vasculature and hard tissue such as bone is complex. Previous studies have indicated that the perfusion of a high-*Z* contrast agent resulted in images where vasculature and bone were indistinguishable [73]. In one of our studies, the vasculature of the equine foot was flushed and fixed with paraformaldehyde (PFA). As the PFA was absorbed into the surrounding tissues, the empty vascular lumen filled with air. This air acted as the perfect contrast medium, allowing the vasculature not only to be distinguished from the surrounding soft tissues, but also from the bone (**Figures 2**–**4**).

One criticism of any vascular fixation method is that it could be argued that manually pressurising the vessels is subjective and could lead to a degree of variability in visible vessel diameter. This method may therefore be useful when comparing similarly fixed tissues, but its variable nature should be kept in mind when direct measurements are being taken The system is not being visualised *in vivo*, but this does reflect observations made under histopathology conditions for example.

*In vivo* CT scanning is advancing rapidly and the use of single photon emission computed tomography (SPECT) that utilises a radiolabelled tracer has shown that the technique works well in animals. Following its use in humans, SPECT was used to assess cerebral blood flow in canine hepatic encephalopathy patients [74]. Comparing both healthy and hepatic encephalopathy canine patients, hypoperfusion was observed for the first time in the temporal cortex subcortical region. Not only was this condition comparable to humans, but also showed that the scanning method was well tolerated by the animals and that the technique itself was comparable to human studies [74]. In addition to the use of tracers and air to differentiate vasculature, a number of researchers have used corrosions casting in order to understand vascularisation in a number of disorders and systems, ranging from kidney development to ocular disorders in species from mice through to sheep [75–77].

Computed Tomography in Veterinary Medicine: Currently Published and Tomorrow's Vision http://dx.doi.org/10.5772/intechopen.68556 279

rather than an overall impression of perfusion rate based on X-ray attenuation of contrast agents in numerous vessels simultaneously. Naturally, in the case of μCT, the post-mortem nature of the samples renders speculation on vasoactivity impossible, but this technique can

A number of different functions can now be investigated in relation to vasculature using CT. Complex 3D models of whole or partial organism vasculature can show areas of angiogenesis and neovascularisation. This technique can also show network interactions, show where vascular junctions and branching occurs, and indicate lumen diameter within a given area. There is an added complexity with blood vessels in that once blood flow ceases, the vascular morphology is altered. In order to preserve the tissues and permit a good visibility of the vasculature once scanned, tissues can be perfused and fixed while fresh. The aim of fixation is to maintain tissues in a life-like state, and perfusion fixation provides the optimal route for the fixative to reach the tissues upon which it can quickly act [72], while fixing the blood vessels in such a way to prevent their collapse and allow them to fill with air, providing the contrast between vessel lumen and the surrounding tissues. Achieving a balance in contrast between soft tissues, vasculature and hard tissue such as bone is complex. Previous studies have indicated that the perfusion of a high-*Z* contrast agent resulted in images where vasculature and bone were indistinguishable [73]. In one of our studies, the vasculature of the equine foot was flushed and fixed with paraformaldehyde (PFA). As the PFA was absorbed into the surrounding tissues, the empty vascular lumen filled with air. This air acted as the perfect contrast medium, allowing the vasculature not only to be distinguished from the surrounding soft tissues, but also from

One criticism of any vascular fixation method is that it could be argued that manually pressurising the vessels is subjective and could lead to a degree of variability in visible vessel diameter. This method may therefore be useful when comparing similarly fixed tissues, but its variable nature should be kept in mind when direct measurements are being taken The system is not being visualised *in vivo*, but this does reflect observations made under histopa-

*In vivo* CT scanning is advancing rapidly and the use of single photon emission computed tomography (SPECT) that utilises a radiolabelled tracer has shown that the technique works well in animals. Following its use in humans, SPECT was used to assess cerebral blood flow in canine hepatic encephalopathy patients [74]. Comparing both healthy and hepatic encephalopathy canine patients, hypoperfusion was observed for the first time in the temporal cortex subcortical region. Not only was this condition comparable to humans, but also showed that the scanning method was well tolerated by the animals and that the technique itself was comparable to human studies [74]. In addition to the use of tracers and air to differentiate vasculature, a number of researchers have used corrosions casting in order to understand vascularisation in a number of disorders and systems, ranging from kidney development to ocular disorders in species from mice through to

still provide insights into vascularisation.

278 Computed Tomography - Advanced Applications

the bone (**Figures 2**–**4**).

thology conditions for example.

sheep [75–77].

**Figure 2.** Vasculature of the equine foot. (A) Dorsally, (B) cranially, (C) laterally/medially, (D) laterally/medially, (E) ventrally, and (F) caudally. Scan spatial resolution = 120 μm.

**Figure 3.** Cranial and caudal views of equine hoof bones and vasculature. (A) Cranially as a whole, (B) cranially as a mid-P3 coronal cut, (C) caudally as a mid-navicular coronal cut, (D) cranolaterally/cranomedially as a whole, (E) caudally as a whole, and (F) ventrocaudally as a coronal cut just cranial of P2 to include only P3. Scan spatial resolution = 120 μm.

**Figure 4.** Blood vessel lumen rendered CT images. (A) Entire equine foot from a palmar/plantar perspective, and (B) from a lateral perspective. Lumen size was mapped, where increasing brightness indicates thicker vessels using BoneJ plugin for ImageJ [42]. Scan spatial resolution = 120 μm.

### **7. The future of CT in veterinary medicine and research**

This chapter has explored the development of CT techniques and their uses, and has shown some of the present research in both the clinical and laboratory setting. Many of the examples shown throughout present ideas for uses in veterinary medicine and science, in addition to indications about where further research is required. Further advancements of CT in the clinic have frequently been directed at using the technology available alongside movementrestricting devices to produce images without general anaesthesia. This is important in patients who may be compromised by the use of anaesthetic drugs. The use of movement-restricting devices with or without sedation can be used to produce diagnostic CT images, and can thus be used to decrease the morbidity rates associated with the use of general anaesthetics [78].

Dynamic imaging, using contrast-enhanced CT and MRI, for the exploration of cerebral and tumour microvasculature is an ever-expanding area of interest [79]. As it stands, such dynamic imaging techniques have not been employed in all disorders but would be of benefit, especially in other highly vascularised structures which can undergo extreme pathogenic changes. The utilisation of such techniques could revolutionise our understanding of the complex pathologies of many areas of the body and differing pathological situations.

Exploitation of the unique characteristics of a synchrotron radiation based μCT facilities could render dynamic experimentation possible, enabling the full elucidation the pathogenic mechanisms involved in differing diseases and disorders in addition to understanding basic anatomical structures. This might involve the visualisation of cellular changes, in addition to tissue alterations. One significant advancement would be to keep tissues metabolically alive and submit them to a variety of physical and chemical stressors, measuring cellular response with the aid of antibody-conjugated high-*Z* nanoparticles in conjunction with synchrotronsourced X-ray CT. Synchrotron-based μCT offers high spatial resolution which, when wishing to view microscopic components of large, intact specimens, could very rapidly become a limiting factor. It is this feature that would render dynamic imaging of constantly evolving structures possible. Studies in live blowfly showed the mechanisms behind their flight motors however it also caused damage to the organisms which died shortly after the experiments [80]. A study designed to show the effects of synchrotron-sourced X-ray CT in ants, grasshoppers, beetles and fruit flies indicated that differing protocols could attenuate cell and system damage, thus making it a more viable imaging source if the protocols were carefully developed [81]. μCT has been utilised to study insects such as the Painted Lady chrysalis, many of the pupae hatched despite multiple scans, but the samples were also immobile thus making μCT scans possible [82]. It should also be highlighted that insects generally tolerate radiation much better than mammalian cells [83]. Naturally the expense and space requirement needed for such high calibre machines and experimental set up restricts these possibilities in the normal clinical setting but is increasingly possible under research conditions.

An equally important and expanding use of CT in veterinary medicine and research is the use of images in order to create 3D reconstructions. This may assist the surgeon prior to surgery or during the recovery period. In addition, the images and 3D reconstructions can be an invaluable teaching tool. Whether teaching young children, undergraduates or surgeons,

**Figure 4.** Blood vessel lumen rendered CT images. (A) Entire equine foot from a palmar/plantar perspective, and (B) from a lateral perspective. Lumen size was mapped, where increasing brightness indicates thicker vessels using BoneJ plugin

**Figure 3.** Cranial and caudal views of equine hoof bones and vasculature. (A) Cranially as a whole, (B) cranially as a mid-P3 coronal cut, (C) caudally as a mid-navicular coronal cut, (D) cranolaterally/cranomedially as a whole, (E) caudally as a whole, and (F) ventrocaudally as a coronal cut just cranial of P2 to include only P3. Scan spatial resolution = 120 μm.

for ImageJ [42]. Scan spatial resolution = 120 μm.

280 Computed Tomography - Advanced Applications

they are a reusable and valuable addition to the mechanisms available. The uses range from teaching anatomy and physiology using 2D pictures, 3D videos, in virtual museums or even 3D printed examples and providing virtual dissection experiences through to their use as moulds for creating devices and as practise for surgery [84]. The use of CT in forensics and archaeology has also risen in line with the technologies available, although in many cases it would be suggested that this field is still 'emerging'. To date in forensics, this has included identifying tool marks on bones, age determination, assessing gunshot wounds, analysing teeth, understanding the pathology of bones and estimating post-mortem intervals [85, 86]. These and the use of CT in many other situations are essential in the development of the veterinary profession and research. A high profile human example was the use of CT and μCT in establishing the cause of death, and injuries sustained by King Richard III who died in the Battle of Bosworth, England in 1485 [87]. His skeleton was excavated in 2012 and thereafter researchers sought to identify the body and to understand the skeleton and injuries. The information from the CT analysis, alongside DNA evidence [88] was used to help unravel the story behind the royal skeleton.

The laboratory CT, synchrotron imaging and software developed, is increasingly utilised to investigate areas previously imaged using histological and gross anatomical techniques, such as measuring vasculature and angiogenesis, bone morphology, assessing cell proliferation and identifying soft tissue structure and morphology. A number of studies use a variety of these techniques simultaneously to achieve insights into veterinary medicine and science. Many of the techniques discussed in this chapter have been used in the research and/or university setting. A challenge to the frequency of use and to use in the clinical setting of these techniques is the availability of equipment and expertise in these very challenging methodologies. The research does enable studies to be carried out to show proof of concept and to develop protocols, which can then be used within the clinical setting. With increasing levels of sophistication of both CT scanning units and associated software, this field presents an ever changing and dynamic field. The next generation of imaging techniques includes nano-CT, which can already achieve resolutions of 400 nm [89], and new software and algorithms that are frequently being designed and advance the present uses of available hardware. Nano-CT has been used in a number of animal based studies ranging from morphological features of osteocyte lacunae in murine bones [90] and comprehending cephalopod chamber formation, morphology and evolution [91], through to musculoskeletal and vascular research in the rat [92, 93]. As always, the key to advancing clinical techniques is the sharing of world class research alongside the financial ability to provide a service according to the needs of the patient.

### **Acknowledgements**

This work was supported by the Biotechnology and Biological Sciences Research Council [grant number BB/I024291/1], by generous funding to Catrin S. Rutland and from the School of Veterinary Medicine and Science, University of Nottingham. This work was also supported by The Weston Scholarship to Catrin S. Rutland and Cyril Rauch to fund Emily Paul. All scanning was carried out on a GE phoenix v|tome|x m (General Electric, Germany, 2013) at The Hounsfield Facility, School of Biosciences, University of Nottingham. The Hounsfield Facility is supported by funding from European Research Council (Futureroots Project), the BBSRC and The Wolfson Foundation.

The Authors would like to thank Dr Agata Witkowska and Dr Ramzi Al-Agele for collecting and preparing CT samples. Ethical permission was given by The University of Nottingham Ethical Committee to collect the naturally deceased guinea pigs and slaughterhouse equine cadavers used to create the figures presented in this chapter.

### **Author details**

they are a reusable and valuable addition to the mechanisms available. The uses range from teaching anatomy and physiology using 2D pictures, 3D videos, in virtual museums or even 3D printed examples and providing virtual dissection experiences through to their use as moulds for creating devices and as practise for surgery [84]. The use of CT in forensics and archaeology has also risen in line with the technologies available, although in many cases it would be suggested that this field is still 'emerging'. To date in forensics, this has included identifying tool marks on bones, age determination, assessing gunshot wounds, analysing teeth, understanding the pathology of bones and estimating post-mortem intervals [85, 86]. These and the use of CT in many other situations are essential in the development of the veterinary profession and research. A high profile human example was the use of CT and μCT in establishing the cause of death, and injuries sustained by King Richard III who died in the Battle of Bosworth, England in 1485 [87]. His skeleton was excavated in 2012 and thereafter researchers sought to identify the body and to understand the skeleton and injuries. The information from the CT analysis, alongside DNA evidence [88] was used to help unravel

The laboratory CT, synchrotron imaging and software developed, is increasingly utilised to investigate areas previously imaged using histological and gross anatomical techniques, such as measuring vasculature and angiogenesis, bone morphology, assessing cell proliferation and identifying soft tissue structure and morphology. A number of studies use a variety of these techniques simultaneously to achieve insights into veterinary medicine and science. Many of the techniques discussed in this chapter have been used in the research and/or university setting. A challenge to the frequency of use and to use in the clinical setting of these techniques is the availability of equipment and expertise in these very challenging methodologies. The research does enable studies to be carried out to show proof of concept and to develop protocols, which can then be used within the clinical setting. With increasing levels of sophistication of both CT scanning units and associated software, this field presents an ever changing and dynamic field. The next generation of imaging techniques includes nano-CT, which can already achieve resolutions of 400 nm [89], and new software and algorithms that are frequently being designed and advance the present uses of available hardware. Nano-CT has been used in a number of animal based studies ranging from morphological features of osteocyte lacunae in murine bones [90] and comprehending cephalopod chamber formation, morphology and evolution [91], through to musculoskeletal and vascular research in the rat [92, 93]. As always, the key to advancing clinical techniques is the sharing of world class research alongside the financial ability to provide a service according to the needs of the patient.

This work was supported by the Biotechnology and Biological Sciences Research Council [grant number BB/I024291/1], by generous funding to Catrin S. Rutland and from the School of Veterinary Medicine and Science, University of Nottingham. This work was also supported by The Weston Scholarship to Catrin S. Rutland and Cyril Rauch to fund Emily Paul.

the story behind the royal skeleton.

282 Computed Tomography - Advanced Applications

**Acknowledgements**

Matthew Keane1†, Emily Paul1†, Craig J Sturrock2 , Cyril Rauch1 and Catrin Sian Rutland1 \*


† Joint first authors

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## *Edited by Ahmet Mesrur Halefoglu*

The advent and rapid diffusion of advanced multidetector-row scanner technology offers comprehensive evaluation of different anatomic structures in daily practice. The aim of this book is to introduce the applications of CT imaging in not only general medicine but also in different fields especially in veterinary medicine, dentistry, and engineering. Recent developments in CT technology have led to a widening of its applications on many areas like material testing in engineering, 3D evaluation of teeth, and the vascular and cardiac evaluations of small animals.

Computed Tomography - Advanced Applications

Computed Tomography

Advanced Applications

*Edited by Ahmet Mesrur Halefoglu*

Photo by Zinkevych / iStock