**7. Ultrasound-based guidance of minimally invasive procedures**

While the main focus of this chapter will be navigation and image guidance using 3D ultra‐ sound images, conventional 2D ultrasound is used for guidance in a variety of clinical applications. The simplest form of ultrasound guidance is placement of a needle inside a target using freehand 2D ultrasound imaging. First, the operator has to localize the target using ultrasound imaging, and second place the needle inside the target while keeping the needle tip in the image plane in order to verify its position. This technique requires a skilled and experienced operator due to the difficulty in keeping the needle in the image plane and the fact that the ultrasound image is not oriented relative to the patient. Despite the difficulties, this technique has been used for biopsies of the liver [99-101], lung [102] and prostate [103], placement of central vein catheters [104, 105] and for brain operations [106].

**Figure 20.** Automatic method for evaluating the accuracy in ultrasound-based navigation. A) The phantom with a sin‐ gle wire cross in the middle of the water tank and a reference frame in the front. B) Physical wire cross in green and an ultrasound volume of the wire cross in gray. C) The ultrasound data is segmented (red) and a small mismatch to the gold standard in green can be observed, i.e. small inaccuracies exist. D) Centerlines of the green and red wire crosses. E) Iterative closest point (ICP) registration between the two centerlines, initial correspondence shown. F) After some iterations. Final results showing the centerlines (G) and the wire crosses (H). The displacement is equal to the NSA.

A slightly more advanced technique for 2D ultrasound guidance includes a needle guide mounted on the ultrasound probe. The guide will ensure that the needle tip is in the image plane at a given depth depending of the ultrasound image sector and the angle of the needle guide. The angle of the needle guide has to be adapted to the depth of the target. Even though this system provides assistance in keeping the needle in the image plane, the operator has to do imaging and puncturing at the same time. In addition, the orientation issues concerning the ultrasound image relative to the patient is not solved and the anatomical overview is restricted to the current real time 2D image. However, the method is fast, does not require specialized equipment or complicated logistics, and provides sufficient guidance for a number of applications such as biopsy of thyroid nodules [107], placement of ventricular catheters in the brain [108, 109] and amniocentesis [110].

#### **7.1. Ultrasound-based navigation in neurosurgery**

= Overall NSA < 1.5 mm + Sound speed uncertainty 0 – 2.0 mm + Brain shift 0 – 10.0 mm = Overall clinical NSA 1.5 – 10.5 mm

these conditions are not met, the accuracy becomes poorer.

**6.3. Method for assessing ultrasound-based navigation accuracy**

As can be seen from table 1 it is possible to achieve an overall clinical NSA close to the NSA found in the laboratory under favorable conditions, i.e., when the speed of sound used in the scanner is close to the average speed of sound in the tissue imaged, and the ultrasound volumes are frequently updated. The need for updates can be determined by real-time 2D imaging. If

As we have seen the ultrasound-based NSA found in the lab using a phantom is valid in the OR (Operating Room) as well, under normal conditions. This makes it very interesting to develop a method that can measure the NSA automatically. We have previously suggested a method based on a phantom with 27 wire crosses and correlating an ultrasound sub-image of each cross to a synthetic template of the cross [98], and the method has been used in a thorough accuracy evaluation of a commercial navigation system [97]. We have since that developed a method that seems to be even more robust, in addition to being more flexible and more convenient to integrate in a navigation system (see figure 20). The method can be used for substantially different ultrasound probes and the phantom is easier to build and to measure accurately. The technique is based on sweeping over the single wire cross with the ultrasound probe, reconstruct all the frames into a volume containing the cross, segment and extract the centerline of the cross and register it to a centerline representation of the accurately measured physical cross, acting as a gold standard, using a modified version of the ICP algorithm [86].

**7. Ultrasound-based guidance of minimally invasive procedures**

placement of central vein catheters [104, 105] and for brain operations [106].

While the main focus of this chapter will be navigation and image guidance using 3D ultra‐ sound images, conventional 2D ultrasound is used for guidance in a variety of clinical applications. The simplest form of ultrasound guidance is placement of a needle inside a target using freehand 2D ultrasound imaging. First, the operator has to localize the target using ultrasound imaging, and second place the needle inside the target while keeping the needle tip in the image plane in order to verify its position. This technique requires a skilled and experienced operator due to the difficulty in keeping the needle in the image plane and the fact that the ultrasound image is not oriented relative to the patient. Despite the difficulties, this technique has been used for biopsies of the liver [99-101], lung [102] and prostate [103],

**Table 1.** Overall clinical NSA estimates

54 Advancements and Breakthroughs in Ultrasound Imaging

Neuronavigation is the term used to describe the use of computer-assisted methods to guide or navigate instruments within the confinements of the scull (or spinal column) during surgery. A neuronavigation system should ideally provide high navigation accuracy throughout the surgical procedure. However, the anatomy of the brain is known to shift position after opening of the skull and dura due to drainage of cerebrospinal fluid (CSF), gravity effects and/or removal of tumor masses or hematomas. This shift in the position of the anatomy is often referred to as *brain shift* and has been shown to occur in the early stage of the surgery with displacement values ranging up to several centimeters [111-113]. The brain shift may therefore significantly impair the accuracy of navigation based on preoperative images as the surgery proceeds. Intraoperative ultrasound imaging provides a solution to the brain shift problem. Compared to using only preoperative images for guidance, the navigation of instruments based on recently acquired intraoperative images can be performed with higher accuracy and precision [97].

The combined use of ultrasound imaging and navigation technology has been explored since the early 1990ies. The University of Oulu was one of the pioneers and demonstrated the clinical use of a passive mechanical arm-based navigation system, which could display reconstructions of preoperative images (CT/MR) and corresponding real-time intraoperative ultrasound images [114].

By attaching position sensors (also referred to as 3D localizers) on the ultrasound probe it is possible to establish the relative spatial position of the image pixels, and it is possible to reconstruct 2D images into an image volume, hence the term 3D ultrasound. The localizer attached to the probe is usually ultrasonic, electromagnetic or optic, and the two latter options (optic, electromagnetic) are currently the most established in commercial systems. Hata *et al* described in a paper from 1997 the initial clinical experience with a frame- and armless navigation system incorporating an ultrasound scanner and an ultrasound probe equipped with an ultrasonic positioning sensor [115]. In 1998 Jödicke *et al* presented a system for detection of brain shift, by comparing preoperative MR images and intraoperative 3D ultra‐ sound [116]. The integration of ultrasound and navigation technology was also explored in Trondheim, Norway, and a system with the feasibility of 3D ultrasound and navigation guidance was developed. Using this system Unsgaard et al. performed the first brain tumour operation with 3D ultrasound guidance in 1996, and the system development and clinical experience was described in several papers [117-119]. The technology was further developed and commercialized by the company Sonowand AS (Trondheim, Norway), which is a spinoff company from the research activities of the National Centre for 3D Ultrasound in Neuro‐ surgery (1995-present (2013)) at St. Olavs University Hospital. The technology has been explored for use in several neurosurgical procedures, but its predominant use is within resection of brain tumours [120]. The Sonowand system allows navigation of pre-calibrated tools equipped with an optic localizer, and it allows tools like biopsy forceps to be calibrated to the navigation system *in situ* in the operating room (figure 21) and used for image guided biopsies. The system facilitates simultaneous displays of reformatted image slices of intrao‐ perative ultrasound and any preoperative MR series like T1, T2, FLAIR, etc. that has been registered to the patient. The position of navigated instruments is indicated in the displayed image slices.

adjacent normal brain tissue. If the tumour is located in so-called eloquent regions, harboring important functional tissue for movement, speech or vision, less extensive resections is often the result. Brain tumour surgery can therefore be a delicate balance between obtaining extensive resections and avoiding functional deficits and loss of quality of life due to the

**Figure 21.** The Sonowand Invite® system for intraoperative ultrasound imaging and navigation (A), various tools of the navigation system equipped with optical localizer units showing one phased array ultrasound probe (B), a naviga‐ tion pointer (C), a biopsy forceps (D), and a screen dump of the navigation display showing reformatted MR images in top row, and corresponding reformatted ultrasound images in bottom row (E). The tip of the navigated instrument is

Ultrasound-Based Guidance and Therapy http://dx.doi.org/10.5772/55884 57

3D ultrasound is an established technique for intraoperative imaging in surgery of brain tumours, and is used for localization of the tumour and for resection control. The first acquisition of 3D ultrasound images is usually performed after opening the bone (craniotomy), but before opening the dura. Several ultrasound volumes (typically 3 to 6) are acquired during the operation to compensate for brain shift and to monitor the progress of tumour removal

Preoperative MR data can be displayed along with one or several ultrasound image volumes acquired at different stages of surgery. It may also be possible to import functional MR images to the navigation system. One way of doing this is to import anatomical MR images (e.g. T1/T2/FLAIR) with bold fMRI enhancements and DTI tractography overlaid as contours on the anatomical images [121-123], as shown in figure 23. The navigation system may therefore provide multimodal visualization of medical images, incorporating functional and anatomical

surgical trauma.

indicated with a bright spot in the reformatted image slices

(figure 22).

information.

#### *7.1.1. 3D Ultrasound in intracranial tumour surgery*

Intracranial tumours include primary and secondary tumours in the brain, pituitary gland, and meninges. Primary tumours are neoplasms originating from supportive tissue in the brain, from meninges, or from pituitary tissue. Secondary brain tumours are metastases of malignant cells that originate from a primary tumour situated in another organ of the body that spreads with the blood flow to the brain. Surgery is the primary treatment for most intracranial tumours. The patient's prognosis is in most cases related to the degree of resection of tumour. The surgical goal is usually to perform a total extirpation of the tumour, but without damaging

Compared to using only preoperative images for guidance, the navigation of instruments based on recently acquired intraoperative images can be performed with higher accuracy and

The combined use of ultrasound imaging and navigation technology has been explored since the early 1990ies. The University of Oulu was one of the pioneers and demonstrated the clinical use of a passive mechanical arm-based navigation system, which could display reconstructions of preoperative images (CT/MR) and corresponding real-time intraoperative ultrasound

By attaching position sensors (also referred to as 3D localizers) on the ultrasound probe it is possible to establish the relative spatial position of the image pixels, and it is possible to reconstruct 2D images into an image volume, hence the term 3D ultrasound. The localizer attached to the probe is usually ultrasonic, electromagnetic or optic, and the two latter options (optic, electromagnetic) are currently the most established in commercial systems. Hata *et al* described in a paper from 1997 the initial clinical experience with a frame- and armless navigation system incorporating an ultrasound scanner and an ultrasound probe equipped with an ultrasonic positioning sensor [115]. In 1998 Jödicke *et al* presented a system for detection of brain shift, by comparing preoperative MR images and intraoperative 3D ultra‐ sound [116]. The integration of ultrasound and navigation technology was also explored in Trondheim, Norway, and a system with the feasibility of 3D ultrasound and navigation guidance was developed. Using this system Unsgaard et al. performed the first brain tumour operation with 3D ultrasound guidance in 1996, and the system development and clinical experience was described in several papers [117-119]. The technology was further developed and commercialized by the company Sonowand AS (Trondheim, Norway), which is a spinoff company from the research activities of the National Centre for 3D Ultrasound in Neuro‐ surgery (1995-present (2013)) at St. Olavs University Hospital. The technology has been explored for use in several neurosurgical procedures, but its predominant use is within resection of brain tumours [120]. The Sonowand system allows navigation of pre-calibrated tools equipped with an optic localizer, and it allows tools like biopsy forceps to be calibrated to the navigation system *in situ* in the operating room (figure 21) and used for image guided biopsies. The system facilitates simultaneous displays of reformatted image slices of intrao‐ perative ultrasound and any preoperative MR series like T1, T2, FLAIR, etc. that has been registered to the patient. The position of navigated instruments is indicated in the displayed

Intracranial tumours include primary and secondary tumours in the brain, pituitary gland, and meninges. Primary tumours are neoplasms originating from supportive tissue in the brain, from meninges, or from pituitary tissue. Secondary brain tumours are metastases of malignant cells that originate from a primary tumour situated in another organ of the body that spreads with the blood flow to the brain. Surgery is the primary treatment for most intracranial tumours. The patient's prognosis is in most cases related to the degree of resection of tumour. The surgical goal is usually to perform a total extirpation of the tumour, but without damaging

precision [97].

56 Advancements and Breakthroughs in Ultrasound Imaging

images [114].

image slices.

*7.1.1. 3D Ultrasound in intracranial tumour surgery*

**Figure 21.** The Sonowand Invite® system for intraoperative ultrasound imaging and navigation (A), various tools of the navigation system equipped with optical localizer units showing one phased array ultrasound probe (B), a naviga‐ tion pointer (C), a biopsy forceps (D), and a screen dump of the navigation display showing reformatted MR images in top row, and corresponding reformatted ultrasound images in bottom row (E). The tip of the navigated instrument is indicated with a bright spot in the reformatted image slices

adjacent normal brain tissue. If the tumour is located in so-called eloquent regions, harboring important functional tissue for movement, speech or vision, less extensive resections is often the result. Brain tumour surgery can therefore be a delicate balance between obtaining extensive resections and avoiding functional deficits and loss of quality of life due to the surgical trauma.

3D ultrasound is an established technique for intraoperative imaging in surgery of brain tumours, and is used for localization of the tumour and for resection control. The first acquisition of 3D ultrasound images is usually performed after opening the bone (craniotomy), but before opening the dura. Several ultrasound volumes (typically 3 to 6) are acquired during the operation to compensate for brain shift and to monitor the progress of tumour removal (figure 22).

Preoperative MR data can be displayed along with one or several ultrasound image volumes acquired at different stages of surgery. It may also be possible to import functional MR images to the navigation system. One way of doing this is to import anatomical MR images (e.g. T1/T2/FLAIR) with bold fMRI enhancements and DTI tractography overlaid as contours on the anatomical images [121-123], as shown in figure 23. The navigation system may therefore provide multimodal visualization of medical images, incorporating functional and anatomical information.

toimprovesincegoodultrasoundimagequalityhasdirectconsequencesfortheobtainedclinical

Ultrasound-Based Guidance and Therapy http://dx.doi.org/10.5772/55884 59

**Figure 23.** Example of multimodal visualization in navigation display. Left column shows anatomical MR image slices (FLAIR) with functional data shown as color overlay. The white spots indicate language area, the turquoise contours represent the pyramidal tract, the pink represent fasiculus arcuate (tract between language areas), the yellow repre‐ sents the optic tract. Middle column shows preoperative MR image slices with intraoperative ultrasound acquired af‐ ter some resection as overlay. Right column is identical as the middle, but with ultrasound data acquired prior to the

It's also possible to acquire power Doppler based 3D ultrasound data of the vascular tree in the target area. This can be useful in both tumor and vascular surgery. In tumor operations the objective is to avoid injury to the vessels caused by the surgical instruments. In vascular surgery power Doppler can be useful in surgical treatment of both aneurysms (figure 18G) and arteriovenous malformations (AVMs, figure 15). For surgical treatment of aneurysms this mode is most useful for evaluating the flow in distal vessels after clipping of the aneurysm. In addition, 3D power Doppler can be used to localize peripheral aneurysms and guide direct surgical approaches. For AVM surgery intra-operative 3D power Doppler has been found to be useful in localizing deep-seated AVMs, identifying feeders and draining veins and for resection control [129]. Navigated display of 3D power Doppler based data can be used to identify and clip the larger feeders of AVMs in the initial phase of the operation, thus making

start of the resection.

*7.1.2. 3D Ultrasound in intracranial vascular surgery*

it easier to perform the extirpation of the AVM.

results, both in terms of resection grades [127] and for patient's quality of life [128].

**Figure 22.** Navigation display showing two perpendicular reformatted image slices from each image volume. Preoper‐ ative MR slices in top row followed by slices from 3 different ultrasound volumes acquired at different stages in the operation. The ultrasound volumes in row 2, 3, and 4 were acquired prior to the resection, during the resection with some tumor tissue remaining, and after the end of the resection, respectively

Clinically, modern image technology has enabled more targeted surgical approaches, as compared to standardized explorative brain dissections that were more common two decades ago.This reduces the surgicaltrauma, easesanatomicalorientationwithinthe surgicalfield,and makes it possible for less experienced surgeons to obtain the same results as their more experi‐ enced peers. Today, even in eloquent regions where surgery is associated with increased risk, good clinical results can be obtained [121]. We have also observed that survival increased after the introduction of 3D ultrasound imaging in malignant primary brain tumour surgery [124]. Intraoperative imaging with ultrasound has also enabled more aggressive treatment strat‐ egies in tumours that microscopically resemble the brain tissue and therefore are difficult to removewithsufficient accuracy.Thishas improvedsurvivalwithout compromisingrisks [125]. Tailored probes designed for special surgical procedures such as the transphenoidal approach [126]throughthenosecanguideoperationsinnarrowapproacheswithlimitedabilitiesfordirect visualization.Withfurtherdevelopmentsinultrasoundtechnology,clinicalresultscancontinue toimprovesincegoodultrasoundimagequalityhasdirectconsequencesfortheobtainedclinical results, both in terms of resection grades [127] and for patient's quality of life [128].

**Figure 23.** Example of multimodal visualization in navigation display. Left column shows anatomical MR image slices (FLAIR) with functional data shown as color overlay. The white spots indicate language area, the turquoise contours represent the pyramidal tract, the pink represent fasiculus arcuate (tract between language areas), the yellow repre‐ sents the optic tract. Middle column shows preoperative MR image slices with intraoperative ultrasound acquired af‐ ter some resection as overlay. Right column is identical as the middle, but with ultrasound data acquired prior to the start of the resection.

#### *7.1.2. 3D Ultrasound in intracranial vascular surgery*

Clinically, modern image technology has enabled more targeted surgical approaches, as compared to standardized explorative brain dissections that were more common two decades ago.This reduces the surgicaltrauma, easesanatomicalorientationwithinthe surgicalfield,and makes it possible for less experienced surgeons to obtain the same results as their more experi‐ enced peers. Today, even in eloquent regions where surgery is associated with increased risk, good clinical results can be obtained [121]. We have also observed that survival increased after the introduction of 3D ultrasound imaging in malignant primary brain tumour surgery [124]. Intraoperative imaging with ultrasound has also enabled more aggressive treatment strat‐ egies in tumours that microscopically resemble the brain tissue and therefore are difficult to removewithsufficient accuracy.Thishas improvedsurvivalwithout compromisingrisks [125]. Tailored probes designed for special surgical procedures such as the transphenoidal approach [126]throughthenosecanguideoperationsinnarrowapproacheswithlimitedabilitiesfordirect visualization.Withfurtherdevelopmentsinultrasoundtechnology,clinicalresultscancontinue

some tumor tissue remaining, and after the end of the resection, respectively

58 Advancements and Breakthroughs in Ultrasound Imaging

**Figure 22.** Navigation display showing two perpendicular reformatted image slices from each image volume. Preoper‐ ative MR slices in top row followed by slices from 3 different ultrasound volumes acquired at different stages in the operation. The ultrasound volumes in row 2, 3, and 4 were acquired prior to the resection, during the resection with

> It's also possible to acquire power Doppler based 3D ultrasound data of the vascular tree in the target area. This can be useful in both tumor and vascular surgery. In tumor operations the objective is to avoid injury to the vessels caused by the surgical instruments. In vascular surgery power Doppler can be useful in surgical treatment of both aneurysms (figure 18G) and arteriovenous malformations (AVMs, figure 15). For surgical treatment of aneurysms this mode is most useful for evaluating the flow in distal vessels after clipping of the aneurysm. In addition, 3D power Doppler can be used to localize peripheral aneurysms and guide direct surgical approaches. For AVM surgery intra-operative 3D power Doppler has been found to be useful in localizing deep-seated AVMs, identifying feeders and draining veins and for resection control [129]. Navigated display of 3D power Doppler based data can be used to identify and clip the larger feeders of AVMs in the initial phase of the operation, thus making it easier to perform the extirpation of the AVM.

Power Doppler based 3D ultrasound data are usually displayed in reddish color superimposed on the B-mode ultrasound slices, but the vessels are usually shown in a more optimal way using 3D rendering techniques. The power Doppler signal is often too intense and smeared out to give a sharp delineation of the small vessels. Robust acquisition of power Doppler based 3D ultrasound data of sufficient quality is essential for vessel-based shift correction and it's important to increase the spatial resolution of such data in the coming years.

#### **7.2. Ultrasound-based navigation in laparoscopic surgery**

Open surgery is the gold standard for abdominal surgeries. But over the last few decades, there has been an increasing demand to shift from open surgery to a minimally invasive approach to make the intervention and the post-operative phase less traumatizing for the patient. Advantages of laparoscopic surgery include decreased morbidity, reduced costs for society (less hospital time and quicker recovery), and also improved long-term outcomes when compared to open surgery. During laparoscopy, the surgeons make use of a video camera for instrument guidance. However, the video laparoscope can only provide two-dimensional (2D) surface visualization of the abdominal cavity. Laparoscopic ultrasound (LUS) provides information beyond the surface of the organs, and was therefore introduced by Yamakawa and coworkers in 1958 [130]. In 1991, Jakimowicz and Reuers introduced LUS scanning for examination of the biliary tree during laparoscopic cholecystectomy [131]. It seemed that LUS gave valuable information and has since expanded in use with the increase in laparoscopic procedures. LUS is today applied in laparoscopy in numerous ways for screening, diagnostics and therapeutic purposes [132, 133]. Some examples of use are screening, like stone detection or identification of lymph nodes, diagnostics, like staging of disease or assessment of opera‐ bility and resection range, and therapeutic, like resection guidance or guidance of radio frequency and cryoablation. Harms and coworkers were the first to integrate an electromag‐ netic (EM) tracking sensor into the tip of a conventional laparoscopic ultrasound probe [134] and this made it possible to combine LUS with navigation technology, solving some of the orientation problems experienced when using laparoscopic ultrasound. The combination of navigation technology and LUS is becoming an active field of research to further improve the safety, accuracy, and outcome of laparoscopic surgery.

data that display the true patient anatomy during surgery. Preoperative CT images will, however, still be useful for reference and overview as illustrated in figure 24, showing various display possibilities using LUS and navigation in laparoscopy. An example of simple overlay of tracked surgical tools onto a 3D volume rendering of computerized tomography (CT) images is shown in figure 24A. In this figure, we used the preoperative 3D CT images for initial inthe-OR planning of the procedure. The view direction of the volume was set by the view direction of the laparoscope. The LUS image could be displayed in the same scene, with an indication of the probe position in yellow. Furthermore, when 3D preoperative images are displayed together with 3D LUS, anatomic shifts can easily be visualized and measured, thereby providing updated information of the true patient anatomy to the surgical team as illustrated in figure 24C. This may improve the accuracy and precision of the procedure. Additionally, the tracked position of the LUS probe can be used to display the corresponding slice from a preoperative CT volume, providing improved overview of the position of the LUS image as shown in figure 24D. Having 3D LUS available, it is possible to display these data the same way as traditional orthogonal display of MR and CT volumes, as shown in figure 24E-G. Intraoperative augmented reality visualizations in combination with navigation technology could be valuable for the surgeons [136]. A possible future development, useful

slice (phantom). E-G) Orthogonal slices from a 3D LUS scan (phantom).

**Figure 24.** Illustration of visualization methods for navigation in laparoscopy. A) Navigation during adrenalectomy us‐ ing preoperative CT (3D and 2D). B) Live animal model (pig) experiment showing navigated LUS combined with pre‐ operative images (CT volume rendering). This solves the orientation problems and improves overview. C) Multimodal display of 3D LUS (volume rendering) and 3D CT from an ex vivo experiment showing that the tumor position has changed. D) Anyplane slicing from CT controlled by the LUS probe and overlaying the LUS onto the corresponding CT

Ultrasound-Based Guidance and Therapy http://dx.doi.org/10.5772/55884 61

Navigation, as explained earlier, is the combined use of tracking and imaging technology to provide a visualization of the position of the tip of a surgical instrument relative to a target and surrounding anatomy. Various display and visualizations methods of both instruments and the medical images can be used in laparoscopic surgery. Preoperative images are useful for planning as well as for guidance during the initial phase of the procedure as long as the target area is in the retroperitoneum [135]. When preoperative images are registered to the patient, the surgeon is able to use navigation to plan the surgical pathway from the tip of the instrument to the target site inside the patient. Thus, navigation provides the intuitive correspondence between the patient (physical space), the images (image space that represent the patient) and the tracked surgical instruments. However, when the surgical procedure starts, tissue will shift and deform and preoperative data will no longer represent the true patient anatomy. LUS then makes it possible to update the map for guidance and acquire image

Power Doppler based 3D ultrasound data are usually displayed in reddish color superimposed on the B-mode ultrasound slices, but the vessels are usually shown in a more optimal way using 3D rendering techniques. The power Doppler signal is often too intense and smeared out to give a sharp delineation of the small vessels. Robust acquisition of power Doppler based 3D ultrasound data of sufficient quality is essential for vessel-based shift correction and it's

Open surgery is the gold standard for abdominal surgeries. But over the last few decades, there has been an increasing demand to shift from open surgery to a minimally invasive approach to make the intervention and the post-operative phase less traumatizing for the patient. Advantages of laparoscopic surgery include decreased morbidity, reduced costs for society (less hospital time and quicker recovery), and also improved long-term outcomes when compared to open surgery. During laparoscopy, the surgeons make use of a video camera for instrument guidance. However, the video laparoscope can only provide two-dimensional (2D) surface visualization of the abdominal cavity. Laparoscopic ultrasound (LUS) provides information beyond the surface of the organs, and was therefore introduced by Yamakawa and coworkers in 1958 [130]. In 1991, Jakimowicz and Reuers introduced LUS scanning for examination of the biliary tree during laparoscopic cholecystectomy [131]. It seemed that LUS gave valuable information and has since expanded in use with the increase in laparoscopic procedures. LUS is today applied in laparoscopy in numerous ways for screening, diagnostics and therapeutic purposes [132, 133]. Some examples of use are screening, like stone detection or identification of lymph nodes, diagnostics, like staging of disease or assessment of opera‐ bility and resection range, and therapeutic, like resection guidance or guidance of radio frequency and cryoablation. Harms and coworkers were the first to integrate an electromag‐ netic (EM) tracking sensor into the tip of a conventional laparoscopic ultrasound probe [134] and this made it possible to combine LUS with navigation technology, solving some of the orientation problems experienced when using laparoscopic ultrasound. The combination of navigation technology and LUS is becoming an active field of research to further improve the

Navigation, as explained earlier, is the combined use of tracking and imaging technology to provide a visualization of the position of the tip of a surgical instrument relative to a target and surrounding anatomy. Various display and visualizations methods of both instruments and the medical images can be used in laparoscopic surgery. Preoperative images are useful for planning as well as for guidance during the initial phase of the procedure as long as the target area is in the retroperitoneum [135]. When preoperative images are registered to the patient, the surgeon is able to use navigation to plan the surgical pathway from the tip of the instrument to the target site inside the patient. Thus, navigation provides the intuitive correspondence between the patient (physical space), the images (image space that represent the patient) and the tracked surgical instruments. However, when the surgical procedure starts, tissue will shift and deform and preoperative data will no longer represent the true patient anatomy. LUS then makes it possible to update the map for guidance and acquire image

important to increase the spatial resolution of such data in the coming years.

**7.2. Ultrasound-based navigation in laparoscopic surgery**

60 Advancements and Breakthroughs in Ultrasound Imaging

safety, accuracy, and outcome of laparoscopic surgery.

**Figure 24.** Illustration of visualization methods for navigation in laparoscopy. A) Navigation during adrenalectomy us‐ ing preoperative CT (3D and 2D). B) Live animal model (pig) experiment showing navigated LUS combined with pre‐ operative images (CT volume rendering). This solves the orientation problems and improves overview. C) Multimodal display of 3D LUS (volume rendering) and 3D CT from an ex vivo experiment showing that the tumor position has changed. D) Anyplane slicing from CT controlled by the LUS probe and overlaying the LUS onto the corresponding CT slice (phantom). E-G) Orthogonal slices from a 3D LUS scan (phantom).

data that display the true patient anatomy during surgery. Preoperative CT images will, however, still be useful for reference and overview as illustrated in figure 24, showing various display possibilities using LUS and navigation in laparoscopy. An example of simple overlay of tracked surgical tools onto a 3D volume rendering of computerized tomography (CT) images is shown in figure 24A. In this figure, we used the preoperative 3D CT images for initial inthe-OR planning of the procedure. The view direction of the volume was set by the view direction of the laparoscope. The LUS image could be displayed in the same scene, with an indication of the probe position in yellow. Furthermore, when 3D preoperative images are displayed together with 3D LUS, anatomic shifts can easily be visualized and measured, thereby providing updated information of the true patient anatomy to the surgical team as illustrated in figure 24C. This may improve the accuracy and precision of the procedure. Additionally, the tracked position of the LUS probe can be used to display the corresponding slice from a preoperative CT volume, providing improved overview of the position of the LUS image as shown in figure 24D. Having 3D LUS available, it is possible to display these data the same way as traditional orthogonal display of MR and CT volumes, as shown in figure 24E-G. Intraoperative augmented reality visualizations in combination with navigation technology could be valuable for the surgeons [136]. A possible future development, useful

**Vendor Probe Frequency Type of probe**

frequency)

Philips / ATL LAP L9-5 5-9 MHz E NA Esaote LP323 4-13 MHz E NA

**Table 2.** LUS probe from various manufacturers. Relevant specifications are also given.

automatically (e.g. seed point set inside the tumor).

ultrasound) is performed to fine tune the patient registration.

perhaps in the OR during other preparations.

landmarks for a rough first approximation.

around the tumor is performed.

image is available as either:

(segmented structures for instance).

and position, or

Gore Tetrad VersaPlane 7.5 MHz (center

to the following clinical scenario:

**(see Fig. 2)**

Being a relatively new area of research, it is interesting to note that the number of active research groups in the field of navigated laparoscopic ultrasound is approximately ten. Based on literature and almost two decades working with surgeons on developments for advanced laparoscopic surgery, a complete system designed for navigated LUS could be used according

**•** The preoperative data are imported and reconstructed into 3D volumes; several structures and organs are segmented automatically (e.g. vessels from contrast CT scan) or semi-

**•** A quick plan is made from the visualization in the navigation system just prior to surgery,

**•** Registration is performed without fiducials using a pointer (orientation of patient) and two

**•** Before mobilizing the target organ (e.g. the liver) a 3D LUS scan of major vessels near or

**•** The LUS images are reconstructed in 3D and an automatic vessel based registration (CT-to-

**•** Augmented reality visualization, e.g. on/off overlay of preoperative data and LUS on the video laparoscope view is preformed as needed by the surgeons during the procedure

**•** 3D LUS scans are updated a few times during the procedure, while the real time 2D LUS

**◦** A full size image with a corresponding indication in a 3D CT rendering of its orientation

**◦** An overlay on the video laparoscope view with or without elements from the CT data

For rigid organ navigation, a single preoperative scan, highly accurate tracking (optical), and rigid surgical tools are sufficient to guide the procedure. However, for soft tissue navigation, additional tools are needed due to deformation and mobile organs in the abdominal cavity, resulting in more complex systems and additional devices in the OR. LUS can provide real time behind-the-surface information (tissue, blood flow, elasticity). When combined with

E 56 mm

**Transducer length, scan angle, other**

Ultrasound-Based Guidance and Therapy http://dx.doi.org/10.5772/55884 63

**Figure 25.** Different LUS probes.

for spotting the true position of lesions and vessels and hence detect anatomic shifts quickly, would be to introduce LUS data into such a multimodal display.

Intraoperative ultrasound systems are inexpensive, compact, mobile, and have no require‐ ments for special facilities in the operating room (OR) compared to MRI or CT. Ultrasound image quality is continuously improving and for certain cases (e.g. liver) LUS could obtain image quality comparable to what is achieved in neurosurgery, as the probe is placed directly on the surface of the organ. In neurosurgery, the image quality of ultrasound has been demonstrated above. The most common LUS probe is a flexible 2- or 4-way array, linear or curved, with a frequency range of 5-10 MHz. Typical imaging depths are in the range 0-10 cm, but with 5MHz deeper imaging can be performed. The LUS transducers usually have a footprint of less than 10 mm wide to fit through trocars and 20-50 mm long. They can be manipulated at the shaft allowing real time images at user-controlled orientations and positions, depending only on the specific probe configuration. Figure 25 shows various configurations of LUS probes, while Table 2 provides an overview of currently available probes. Most LUS probes [137] can be sterilized [138].



**Table 2.** LUS probe from various manufacturers. Relevant specifications are also given.

for spotting the true position of lesions and vessels and hence detect anatomic shifts quickly,

Intraoperative ultrasound systems are inexpensive, compact, mobile, and have no require‐ ments for special facilities in the operating room (OR) compared to MRI or CT. Ultrasound image quality is continuously improving and for certain cases (e.g. liver) LUS could obtain image quality comparable to what is achieved in neurosurgery, as the probe is placed directly on the surface of the organ. In neurosurgery, the image quality of ultrasound has been demonstrated above. The most common LUS probe is a flexible 2- or 4-way array, linear or curved, with a frequency range of 5-10 MHz. Typical imaging depths are in the range 0-10 cm, but with 5MHz deeper imaging can be performed. The LUS transducers usually have a footprint of less than 10 mm wide to fit through trocars and 20-50 mm long. They can be manipulated at the shaft allowing real time images at user-controlled orientations and positions, depending only on the specific probe configuration. Figure 25 shows various configurations of LUS probes, while Table 2 provides an overview of currently available

**(see Fig. 2)**

**Transducer length, scan angle, other**

would be to introduce LUS data into such a multimodal display.

**Figure 25.** Different LUS probes.

62 Advancements and Breakthroughs in Ultrasound Imaging

probes. Most LUS probes [137] can be sterilized [138].

**Vendor Probe Frequency Type of probe**

Aloka UST-52109 3-7.5 MHz A 10 mm, 90°

Toshiba PEF 704LA 5, 7.5, 10 MHz E 34 mm

UST-5524-LAP 4-10 MHz E 38 mm UST-5526L-7.5 5-10 MHz D 33 mm UST-5536-7.5 5-10 MHz E 38 mm

Hitachi EUP OL531 5-10 MHz C 120°, Biopsy and therapy

PVM 787LA 5, 7.5, 10 MHz B 85°

BK Medical 8666-RF 5-10 MHz E 30 mm, Puncture and biopsy guide

Being a relatively new area of research, it is interesting to note that the number of active research groups in the field of navigated laparoscopic ultrasound is approximately ten. Based on literature and almost two decades working with surgeons on developments for advanced laparoscopic surgery, a complete system designed for navigated LUS could be used according to the following clinical scenario:

	- **◦** A full size image with a corresponding indication in a 3D CT rendering of its orientation and position, or
	- **◦** An overlay on the video laparoscope view with or without elements from the CT data (segmented structures for instance).

For rigid organ navigation, a single preoperative scan, highly accurate tracking (optical), and rigid surgical tools are sufficient to guide the procedure. However, for soft tissue navigation, additional tools are needed due to deformation and mobile organs in the abdominal cavity, resulting in more complex systems and additional devices in the OR. LUS can provide real time behind-the-surface information (tissue, blood flow, elasticity). When combined with advanced visualization techniques and preoperative images, LUS can enhance an augmented reality scene to include updated images of details, important for high precision surgery thus enhancing the perception for surgeons during minimal access therapy. LUS integrated with miniaturized tracking technology is likely to play an important role in guiding future laparo‐ scopic surgery.

3D ultrasound has also been used to guide surgery of the spine. Kolstad et al [149] reported in 2006 a study, where spinal cord tumors were visualized using ultrasound imaging, and 3D ultrasound-guided tumor resection were performed using navigation technology. The technical application of integrating ultrasound and navigation seems feasible since it solves the orientation problem with conventional 2D ultrasound and may have the potential of

Ultrasound-Based Guidance and Therapy http://dx.doi.org/10.5772/55884 65

High-intensity focused ultrasound (HIFU or FUS) has been known and developed for decades and can be applied to produce sharply delineated lesions in biological tissue (figure 26) [150-153]. The development of magnetic resonance (MR) thermometry enabled the thermal ablation progress to be monitored during sonication [154]. MR-guided HIFU (MRgFUS) has been approved by the FDA for the symptomatic treatment of uterine fibroids since 2004 [155]; clinical trials have been reported for breast [156, 157] and brain [158, 159] therapy, as well as pain palliation in bone [160, 161]. The MRgFUS treatment of abdominal organs, such as the kidney, pancreas or liver, poses additional technological and clinical challenges. First, for most therapeutic applications within the human body, tissue displacement caused by respiration and/or the cardiac cycle must be considered, and can be assumed to be periodic in anaesthe‐ tized patients. However, this may not be the case for free-breathing patients. This movement in addition to drift due to gravity and the intestine and bowel movement is important to account for during sonication in order to achieve accurately located FUS with respect to the target (e.g. tumour in the liver). Secondly, the presence of the rib cage affects the HIFU treatment planning and set-up. The rib cage acts as an aberrator that might affect the focusing [162, 163] and on the other hand, due to the high value of the absorption coefficient of the bone [164], the overheating on the ribs can be quite significant. These two aspects are currently the

main challenges in order to achieve MRgFUS in moving abdominal organs.

improving functional outcome of spinal cord tumor surgery.

**8. Ultrasound and non-invasive therapy**

**8.1. High Intensity Focused Ultrasound (HIFU)**

#### **7.3. Other applications**

One of the first, and still one of the most important applications of ultrasound imaging is in diagnostics of various heart conditions. The dynamic real-time imaging makes ultrasound the modality of choice for characterization of a moving organ such as the heart. Some examples of the use of echocardiography are evaluation of cardiovascular anomalies in fetuses and newborns [139], assessment of aortic stenosis [140], evaluation of the function of the valves and examination of the flow and function after heart attacks. These examples are purely diagnostic applications without any kind of intervention associated, but ultrasound has also been used for guidance in cardiac surgery. One example was presented by Wang et al. [141]. They evaluated 129 patients who underwent robotic cardiac surgery. Transesophageal echocardiography was used for guidance of the cannula for peripheral cardiopulmonary bypass. Ultrasound imaging can potentially also be used for guidance in minimally invasive mitral valve repair on the beating heart [123].

Intra-operative guidance during endovascular procedures is usually performed with x-ray fluoroscopy. However, some investigators have reported the use of transabdominal ultra‐ sound for guidance. Lie et al. [142] studied the use of 2D transabdominal ultrasound during endovascular procedures. They found that ultrasound could be useful for guiding the insertion of guidewires, and control the wire position before connecting the second graft limb to the main limb of bifurcated grafts. Kaspersen et al. [143] reported a feasibility study registering ultrasound to pre-operatve CT data. This may be useful for updating the CT data used for navigation and correct for breathing motion and deformation of the blood vessels during the procedure. With recent advances in ultrasound technology, we believe that real-time 3D ultrasound have potential for further advancing the accuracy in the insertion of stentgrafts, and in particular the placement of fenestrated stentgrafts. Specifically, it is easier to track the tip of guidewires in three dimensions, while simultaneously visualizing a focused area of the 3D anatomy in real-time. A systematic review by Malkawi et al [144] concluded that percuta‐ neous endovascular repair was associated with fewer access related complications and reduced operative time. In a study by Arthurs et al [145], it was shown that use of ultrasound guided access significantly reduced access-related complications compared to percutanous access without ultrasound guidance. Successful ultrasound guidance in secondary interven‐ tions, for sealing endoleak after endovascular repair, has also been reported. Boks et al. [146] described transabdominal embolization using duplex ultrasound guidance, and Kasthuri et al. [147] used ultrasound for guiding percutaneous thrombin injection. Navigation of sten‐ tgrafts during endovascular procedures has also been demonstrated in patients using CT imaging [148]. However, 3D or 4D ultrasound integrated with navigation technology for guidance of endovascular procedures has not yet been demonstrated in patients.

3D ultrasound has also been used to guide surgery of the spine. Kolstad et al [149] reported in 2006 a study, where spinal cord tumors were visualized using ultrasound imaging, and 3D ultrasound-guided tumor resection were performed using navigation technology. The technical application of integrating ultrasound and navigation seems feasible since it solves the orientation problem with conventional 2D ultrasound and may have the potential of improving functional outcome of spinal cord tumor surgery.
