*3.2.2. Validation methods*

**Figure 4.** Photograph of hybrid scanner with abdominal ultrasound transducer mounted and ready for scanning.

the tilt mode only.

10 Advancements and Breakthroughs in Ultrasound Imaging

The 3D scanning device has three modes of operation: a linear translation, in which the transducer (oriented perpendicular to the surface or at an angle for Doppler imaging) is translated along a straight line parallel to the patient's surface. This motion generates a rectangular volume shown in Fig. 5a. The second mode generates a tilt motion (or wobbling), in which the transducer is rotated about its face resting on the patient's skin surface (Fig. 5b). The third mode is a combination of the first two modes that creates a combined (or hybrid) motion. The transducer is rotated as it is moved along a surface covering a larger volume than either of the first two modes (Fig. 5c). For example, if transducer with linear array is used at 15cm depth setting on the ultrasound machine (typical depth for abdominal imaging), hybrid scanning gives a volume that is three times larger than the linear mode and 47% larger than

**Figure 5.** Schematic diagrams showing the three modes of operation of the mechanical compound 3D US scanning

device. On the left is the schematic of the linkage and the right are the linear, tilt and hybrid motions.

Since the hybrid scanning mode involves coordination between two acquisition methods, it was tested in terms of accuracy of 3D image generation. We used two custom made phantoms with known geometry. The validation experiments where performed using the handheld 3D US scanning device in hybrid scanning mode using a two-dimensional conventional curved array ultrasound transducer used for abdominal applications (Toshiba, PVT-375BT).

*Geometrical Error in 3D reconstruction*: This test was designed to measure the accuracy of the 3D reconstruction of the 3D hybrid scanner in three directions. The test phantom was made of a grid of known dimensions made with 0.1 mm thick nylon monofilament threads wrapped around an accurately machined frame to form a 4-layer grid. Each layer was slightly shifted from the layer above to avoid acoustic shadowing. The distance between any two layers was 1cm. The phantom was submerged in a 15% glycerol solution [61] and imaged at different depth settings. The acquired 3D US images were then viewed and analyzed by measuring the distances between the images of the monofilaments and comparing them to the expected values.

**Figure 6.** (a) Photograph of the 3D monofilament thread grid, which was used to validate the 3D reconstruction of the ultrasound image. (b) The 3D ultrasound image of the phantom, showing the grid of threads.

*Error in 3D volume measurements:* In the second test, we assessed the accuracy in measuring volumes using our system. For this experiment, several spherical phantoms with different sizes were made of tissue mimicking agar [65]. The volume of each of these spherical phantoms was measured prior to embedding them in a cube of tissue mimicking agar phantom. The spherical phantoms were then imaged with our hybrid scanner, viewed in the 3D visualization software, and manually segmented. The volume of spherical structures were calculated and compared with the expected values.

**4. 3D ultrasound guided prostate biopsy**

Prostate Cancer (PCa) is the most commonly diagnosed malignancy in men, and is found at autopsy in 30% of men at age 50, 40% at age 60, and almost 90% at age 90 [66, 67]. Worldwide, it is the second leading cause of death due to cancer in men, accounting for between 2.1% and 15.2% of all cancer deaths [68, 69]. Symptoms PCa are generally absent until extensive local growth or metastases develop. When diagnosed at an early stage, the disease is curable [70, 71], and even at later stages treatment can be effective [72]; however, once the tumor has extended beyond the prostate, the risk of metastases and locally aggressive cancer increases. Clearly, early diagnosis, accurate staging of prostate cancer, and appropriate therapies are

3D Ultrasound Imaging in Image-Guided Intervention

http://dx.doi.org/10.5772/55230

13

In managing patients with possible PCa, the challenges facing physicians are to: (a) diagnose clinically relevant cancers at a curable stage; (b) stage the disease accurately; (c) apply appro‐ priate therapy accurately to optimize destruction of cancer cells while preserving normal tissues and function; and (d) follow patients to assess side effects and therapy effectiveness. This section focuses on improving early PCa diagnosis and staging with the use of 3D

Since not all cancers are palpable by digital rectal exam (DRE), PCa diagnosis is established by histological examination of prostate tissue obtained most commonly by trans-rectal ultrasound (TRUS)-guided biopsy. Prostate needle biopsy is the only definitive diagnostic modality capable of confirming malignancy, and is now always performed with TRUS

Since many small tumors are not detected by TRUS or DRE, biopsy samples are obtained from predetermined regions of the prostate known to have a high probability of harboring cancer. These are typically in the peripheral zone (PZ), which harbors 80% of all PCs and a higher proportion of clinically significant ones, and close to the capsule, as most cancers are thought to start within 5*mm* of the prostate capsule. Most centers are now taking 8-12 cores or more as

TRUS biopsies are now performed with a thin, 18-gauge needle mounted on a spring-loaded gun connected to the TRUS probe, forcing the needle to stay in the imaging plane. Each core is separately identified as to the prostate region from which it was drawn, so that the pathol‐

Since prostate volume sampled by the biopsy is small, and PCa is often multi-focal, involving only a small volume of the prostate in the early stages of the disease [77, 78], the probability for obtaining a sample of the tumour on biopsy is small. Thus, a negative biopsy may be, in fact, false, and the patient may be harbouring cancer at an early and curable stage. Various reports have shown that the false negative rate ranges from 10% to 25% [73, 74]. Since cancer is still present in 1/10 to 1/4 of patients with a negative first biopsy, the current biopsy procedure is still suboptimal [74, 79]. Clearly, an improved procedure with improved planning and

ogist can report the extent and grade of the cancer within each region.

recording of biopsy locations is necessary to resolve these issues.

**4.1. The clinical problem**

critical to the patient's well-being.

ultrasound-guided prostate biopsy.

part of their routine assessment [73-76].

guidance.

#### *3.2.3. Validation results*

Testing the 3D hybrid scanner with the 3D thread phantom showed that mean error in the measured values of the distances in the X, Y and Z directions were 3.6%, 2.5% and 5.7% respectively. A one-sample t-test was performed to compare the measured distance values with the known distance value of 1cm, showed there was no statistical significant difference between the measured values and expected values between the threads.

Validation of volume measurements using the hybrid scanner were carried out by imaging a tissue mimicking agar sphere with a volume of 10 cm3 embedded in a block of tissue mimicking agar phantom. The measurements were performed at two different depth settings on the ultrasound machine (10 and 15 cm). The mean errors of the volume measurement were 5.7% and 4.4% for the 10cm and 15cm depth settings respectively, demonstrating that the hybrid scanner can be used to make sufficiently accurate volumetric measurements.

*In-vivo experiments:* After obtaining institutional research board (IRB) approvals, we investigat‐ edtheuseofthescannerinthermalablationtreatmentofprimaryhepatictumors.Figure7shows a 3D US image acquired during the microwave ablation procedure of a primary (hepatocellu‐ lar)tumor.Itshowsapplicationofthehybridmodeinacquiringvolumeslargeenoughtoinclude both the ablated tumor region as well as all ablation needles in two different views.

**Figure 7.** 3D ultrasound image of a primary (hepatocellular) tumor with two microwave applicators in place. The ap‐ plicators and tumor have been segmented and displayed in 3D allowing the interventional radiologist to examine the placement accuracy of the applicators in the tumor. In addition, the ablation zone has also been superimposed.
