Reliability and concurrent validity of three-dimensional ultrasound for quantifying knee cartilage volume.

Objective: The goal of this study was to test the reliability and validity of a handheld mechanical three-dimensional (3D) ultrasound (US) device for quantifying femoral articular cartilage (FAC) against the current clinical standard of magnetic resonance imaging (MRI). Design: Bilateral knee images of 25 healthy volunteers were acquired with 3D US and 3.0 T MRI. The trochlear FAC was segmented by two raters who repeated segmentations on five cases during separate sessions. MRI and 3D US segmentations were registered using a semi-automated surface-based registration algorithm, and MRI segmentations were trimmed to match the FAC region from 3D US. Intra- (n = 5) and inter-rater (n = 25) reliabilities were assessed using intraclass correlation coefficients (ICCs) calculated from FAC volumes. Relationships between MRI and 3D US were assessed using Spearman correlation and linear regression (n = 25). Results: MRI intra-rater ICCs were 0.97 (0.79, 1.00) and 0.90 (0.25, 0.99) for each rater with an inter-rater ICC of 0.83 (0.48, 0.94). 3D US intra-rater ICCs were 1.00 (0.98, 1.00) and 0.98 (0.84, 1.00) for each rater with an inter-rater ICC of 0.96 (0.90, 0.98). Spearman correlation and linear regression revealed a strong correlation ρ = 0.884 (0.746, 0.949) and regression R2 = 0.848 (0.750, 0.950). Conclusion: These results suggest 3D US demonstrates excellent intra- and inter-rater reliabilities and strong concurrent validity with MRI when quantifying healthy trochlear FAC volume. 3D US may reduce imaging costs and greatly improve feasibility of quantifying knee cartilage volume during knee arthritis clinical trials and patient care.

Anatomical pulmonary magnetic resonance imaging segmentation for regional structure-function measurements of asthma.

PURPOSE: Pulmonary magnetic-resonance-imaging (MRI) and x-ray computed-tomography have provided strong evidence of spatially and temporally persistent lung structure-function abnormalities in asthmatics. This has generated a shift in their understanding of lung disease and supports the use of imaging biomarkers as intermediate endpoints of asthma severity and control. In particular, pulmonary (1)H MRI can be used to provide quantitative lung structure-function measurements longitudinally and in response to treatment. However, to translate such biomarkers of asthma, robust methods are required to segment the lung from pulmonary (1)H MRI. Therefore, their objective was to develop a pulmonary (1)H MRI segmentation algorithm to provide regional measurements with the precision and speed required to support clinical studies. METHODS: The authors developed a method to segment the left and right lung from (1)H MRI acquired in 20 asthmatics including five well-controlled and 15 severe poorly controlled participants who provided written informed consent to a study protocol approved by Health Canada. Same-day spirometry and plethysmography measurements of lung function and volume were acquired as well as (1)H MRI using a whole-body radiofrequency coil and fast spoiled gradient-recalled echo sequence at a fixed lung volume (functional residual capacity + 1 l). We incorporated the left-to-right lung volume proportion prior based on the Potts model and derived a volume-proportion preserved Potts model, which was approximated through convex relaxation and further represented by a dual volume-proportion preserved max-flow model. The max-flow model led to a linear problem with convex and linear equality constraints that implicitly encoded the proportion prior. To implement the algorithm, (1)H MRI was resampled into ∼3 × 3 × 3 mm(3) isotropic voxel space. Two observers placed seeds on each lung and on the background of 20 pulmonary (1)H MR images in a randomized dataset, on five occasions, five consecutive days in a row. Segmentation accuracy was evaluated using the Dice-similarity-coefficient (DSC) of the segmented thoracic cavity with comparison to five-rounds of manual segmentation by an expert observer. The authors also evaluated the root-mean-squared-error (RMSE) of the Euclidean distance between lung surfaces, the absolute, and percent volume error. Reproducibility was measured using the coefficient of variation (CoV) and intraclass correlation coefficient (ICC) for two observers who repeated segmentation measurements five-times. RESULTS: For five well-controlled asthmatics, forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) was 83% ± 7% and FEV1 was 86 ± 9%pred. For 15 severe, poorly controlled asthmatics, FEV1/FV C = 66% ± 17% and FEV1 = 72 ± 27%pred. The DSC for algorithm and manual segmentation was 91% ± 3%, 92% ± 2% and 91% ± 2% for the left, right, and whole lung, respectively. RMSE was 4.0 ± 1.0 mm for each of the left, right, and whole lung. The absolute (percent) volume errors were 0.1 l (∼6%) for each of right and left lung and ∼0.2 l (∼6%) for whole lung. Intra- and inter-CoV (ICC) were <0.5% (>0.91%) for DSC and <4.5% (>0.93%) for RMSE. While segmentation required 10 s including ∼6 s for user interaction, the smallest detectable difference was 0.24 l for algorithm measurements which was similar to manual measurements. CONCLUSIONS: This lung segmentation approach provided the necessary and sufficient precision and accuracy required for research and clinical studies.

3D ultrasound system to investigate intraventricular hemorrhage in preterm neonates.

Intraventricular hemorrhage (IVH) is a common disorder among preterm neonates that is routinely diagnosed and monitored by 2D cranial ultrasound (US). The cerebral ventricles of patients with IVH often have a period of ventricular dilation (ventriculomegaly). This initial increase in ventricle size can either spontaneously resolve, which often shows clinically as a period of stabilization in ventricle size and eventual decline back towards a more normal size, or progressive ventricular dilation that does not stabilize and which may require interventional therapy to reduce symptoms relating to increased intracranial pressure. To improve the characterization of ventricle dilation, we developed a 3D US imaging system that can be used with a conventional clinical US scanner to image the ventricular system of preterm neonates at risk of ventriculomegaly. A motorized transducer housing was designed specifically for hand-held use inside an incubator using a transducer commonly used for cranial 2D US scans. This system was validated using geometric phantoms, US/MRI compatible ventricle volume phantoms, and patient images to determine 3D reconstruction accuracy and inter- and intra-observer volume estimation variability. 3D US geometric reconstruction was found to be accurate with an error of <0.2%. Measured volumes of a US/MRI compatible ventricle-like phantom were within 5% of gold standard water displacement measurements. Intra-class correlation for the three observers was 0.97, showing very high agreement between observers. The coefficient of variation was between 1.8-6.3% for repeated segmentations of the same patient. The minimum detectable difference was calculated to be 0.63 cm(3) for a single observer. Results from ANOVA for three observers segmenting three patients of IVH grade II did not show any significant differences (p > 0.05) for the measured ventricle volumes between observers. This 3D US system can reliably produce 3D US images of the neonatal ventricular system. There is the potential to use this system to monitor the progression of ventriculomegaly over time in patients with IVH.

3D prostate histology reconstruction: an evaluation of image-based and fiducial-based algorithms.

PURPOSE: Evaluation of in vivo prostate imaging modalities for determining the spatial distribution and aggressiveness of prostate cancer ideally requires accurate registration of images to an accepted reference standard, such as histopathological examination of radical prostatectomy specimens. Three-dimensional (3D) reconstruction of prostate histology facilitates these registration-based evaluations by reintroducing 3D spatial information lost during histology processing. Because the reconstruction accuracy may constrain the clinical questions that can be answered with these data, it is important to assess the tradeoffs between minimally disruptive methods based on intrinsic image information and potentially more robust methods based on extrinsic fiducial markers. METHODS: Ex vivo magnetic resonance (MR) images and digitized whole-mount histology images from 12 radical prostatectomy specimens were used to evaluate four 3D histology reconstruction algorithms. 3D reconstructions were computed by registering each histology image to the corresponding ex vivo MR image using one of two similarity metrics (mutual information or fiducial registration error) and one of two search domains (affine transformations or a constrained subset thereof). The algorithms were evaluated for accuracy using the mean target registration error (TRE) computed from homologous intrinsic point landmarks (3-16 per histology section; 232 total) identified on histology and MR images, and for the sensitivity of TRE to rotational, translational, and scaling initialization errors. RESULTS: The algorithms using fiducial registration error and mutual information had mean ± standard deviation TREs of 0.7 ± 0.4 and 1.2 ± 0.7 mm, respectively, and one algorithm using fiducial registration error and affine transforms had negligible sensitivities to initialization errors. The postoptimization values of the mutual information-based metric showed evidence of errors due to both the optimizer and the similarity metric, and variation of parameters of the mutual information-based metric did not improve its performance. CONCLUSIONS: The extrinsic fiducial-based algorithm had lower mean TRE and lower sensitivity to initialization than the intrinsic intensity-based algorithm using mutual information. A model relating statistical power to registration error for certain imaging validation study designs estimated that a reconstruction algorithm with a mean TRE of 0.7 mm would require 27% fewer subjects than the method used to initialize the algorithms (mean TRE 1.3 ± 0.7 mm), suggesting the choice of reconstruction technique can have a substantial impact on the design of imaging validation studies, and on their overall cost.

Three-dimensional segmentation of three-dimensional ultrasound carotid atherosclerosis using sparse field level sets.

PURPOSE: Three-dimensional ultrasound (3DUS) vessel wall volume (VWV) provides a 3D measurement of carotid artery wall remodeling and atherosclerotic plaque and is sensitive to temporal changes of carotid plaque burden. Unfortunately, although 3DUS VWV provides many advantages compared to measurements of arterial wall thickening or plaque alone, it is still not widely used in research or clinical practice because of the inordinate amount of time required to train observers and to generate 3DUS VWV measurements. In this regard, semiautomated methods for segmentation of the carotid media-adventitia boundary (MAB) and the lumen-intima boundary (LIB) would greatly improve the time to train observers and for them to generate 3DUS VWV measurements with high reproducibility. METHODS: The authors describe a 3D algorithm based on a modified sparse field level set method for segmenting the MAB and LIB of the common carotid artery (CCA) from 3DUS images. To the authors' knowledge, the proposed algorithm is the first direct 3D segmentation method, which has been validated for segmenting both the carotid MAB and the LIB from 3DUS images for the purpose of computing VWV. Initialization of the algorithm requires the observer to choose anchor points on each boundary on a set of transverse slices with a user-specified interslice distance (ISD), in which larger ISD requires fewer user interactions than smaller ISD. To address the challenges of the MAB and LIB segmentations from 3DUS images, the authors integrated regional- and boundary-based image statistics, expert initializations, and anatomically motivated boundary separation into the segmentation. The MAB is segmented by incorporating local region-based image information, image gradients, and the anchor points provided by the observer. Moreover, a local smoothness term is utilized to maintain the smooth surface of the MAB. The LIB is segmented by constraining its evolution using the already segmented surface of the MAB, in addition to the global region-based information and the anchor points. The algorithm-generated surfaces were sliced and evaluated with respect to manual segmentations on a slice-by-slice basis using 21 3DUS images. RESULTS: The authors used ISD of 1, 2, 3, 4, and 10 mm for algorithm initialization to generate segmentation results. The algorithm-generated accuracy and intraobserver variability results are comparable to the previous methods, but with fewer user interactions. For example, for the ISD of 3 mm, the algorithm yielded an average Dice coefficient of 94.4% ± 2.2% and 90.6% ± 5.0% for the MAB and LIB and the coefficient of variation of 6.8% for computing the VWV of the CCA, while requiring only 1.72 min (vs 8.3 min for manual segmentation) for a 3DUS image. CONCLUSIONS: The proposed 3D semiautomated segmentation algorithm yielded high-accuracy and high-repeatability, while reducing the expert interaction required for initializing the algorithm than the previous 2D methods.

Feasibility of 3D ultrasound to evaluate upper extremity nerves.

PURPOSE: This study investigates the performance of a 3 D Ultrasound (US) system in imaging elbow and wrist nerves. MATERIALS AND METHODS: Twenty healthy volunteers with asymptomatic median, ulnar and radial nerves were prospectively investigated. Bilateral 3DUS scans of the elbows and wrists were acquired by using a commercially available US scanner (18 MHz, AplioXG, Toshiba) and stored as a 3 D volume by a dedicated software (CURE, Robarts Research Institute). Retrospectively, qualitative (image quality, atypical nerve location, findings potentially associated with compression neuropathy) and quantitative (cross-sectional area measurements) evaluations were performed. RESULTS: In all 200 nerves 3DUS was feasible (100%). Image quality was insufficient in 13.5% (25 ulnar nerve elbow, 2 radial nerve) and sonomorphology was not assessable in those nerves. Measurement of cross sectional areas was feasible in all nerves (100%). Median cross-sectional area (range) were: median nerve elbow 7 mm2 (6-9), radial nerve 3 mm2 (1-4), ulnar nerve elbow 8 mm2 (5-11), median nerve wrist 8 mm2 (5-10), and ulnar nerve wrist 4 mm2 (2-6). No significant changes in nerve cross-sectional area along each nerve was found. Ulnar nerve subluxation was found in 2 nerves (6.7%). No anconeus epitrochlearis muscle or osteophytes were found. CONCLUSION: 3DUS is a feasible method for assessing nerves of the upper extremity and has been shown to provide a good overview of the median, ulnar and radial nerve at the elbow and wrist, but is limited for evaluation of the ulnar nerve in the cubital tunnel. This technique enables reliable measurements at different locations along the nerve.

Three-dimensional ultrasound of carotid atherosclerosis: semiautomated segmentation using a level set-based method.

PURPOSE: Three-dimensional ultrasound (3D US) of the carotid artery provides measurements of arterial wall and plaque [vessel wall volume (VWV)] that are complementary to the one-dimensional measurement of the carotid artery intima-media thickness. 3D US VWV requires an observer to delineate the media-adventitia boundary (MAB) and lumen-intima boundary (LIB) of the carotid artery. The main purpose of this work was to develop and evaluate a semiautomated segmentation algorithm for delineating the MAB and LIB of the carotid artery from 3D US images. METHODS: To segment the MAB and LIB, the authors used a level set method and combined several low-level image cues with high-level domain knowledge and limited user interaction. First, the operator initialized the algorithm by choosing anchor points on the boundaries, identified in the images. The MAB was segmented using local region- and edge-based energies and an energy that encourages the boundary to pass through anchor points from the preprocessed images. For the LIB segmentation, the authors used local and global region-based energies, the anchor point-based energy, as well as a constraint promoting a boundary separation between the MAB and LIB. The data set consisted of 231 2D images (11 2D images per each of 21 subjects) extracted from 3D US images. The image slices were segmented five times each by a single observer using the algorithm and the manual method. Volume-based, region-based, and boundary distance-based metrics were used to evaluate accuracy. Moreover, repeated measures analysis was used to evaluate precision. RESULTS: The algorithm yielded an absolute VWV difference of 5.0% +/- 4.3% with a segmentation bias of -0.9% +/- 6.6%. For the MAB and LIB segmentations, the method gave absolute volume differences of 2.5% +/- 1.8% and 5.6% +/- 3.0%, Dice coefficients of 95.4% +/- 1.6% and 93.1% +/- 3.1%, mean absolute distances of 0.2 +/- 0.1 and 0.2 +/- 0.1 mm, and maximum absolute distances of 0.6 +/- 0.3 and 0.7 +/- 0.6 mm, respectively. The coefficients of variation of the algorithm (5.1%) and manual methods (3.9%) were not significantly different, but the average time saved using the algorithm (2.8 min versus 8.3 min) was substantial. CONCLUSIONS: The authors generated and tested a semiautomated carotid artery VWV measurement tool to provide measurements with reduced operator time and interaction, with high Dice coefficients, and with necessary required precision.

Evaluation of intersession 3D-TRUS to 3D-TRUS image registration for repeat prostate biopsies.

PURPOSE: 3D-TRUS-guided prostate biopsy permits a 3D record of biopsy cores, supporting the planning of targets to resample or avoid during repeat biopsy sessions. Image registration is required in order to map biopsy targets planned on a previous session's 3D-TRUS image into the context of the current session. The authors evaluated the performance of surface- and intensity-based rigid and nonrigid registration algorithms for this task using a clinically motivated success criterion of a maximum 2.5 mm target registration error (TRE). METHODS: The authors collected two 3D-TRUS images for each of 13 patients, where each image was collected in a separate biopsy session, and the sessions were 1 week apart. The authors tested the iterative closest point and thin-plate spline surface-based registration methods, and the block matching and B-spline intensity-based methods. Manually marked intrinsic fiducials (calcifications) were used to calculate a TRE for each of the tested methods. In addition, error ellipsoids, anisotropy, and variability due to image segmentation were analyzed. All analysis was performed separately for the peripheral zone since this area harbors up to 80% of all prostate cancer. RESULTS: Only the intensity-based nonrigid registration method met the success criterion for both the whole gland and the peripheral zone. Segmentation was a substantial contributor to registration error variability for the surface-based methods, and the surface-based methods resulted in greater error volumes and anisotropy. CONCLUSIONS: Intensity-based rigid registration is clinically sufficient to register regions outside the peripheral zone, but nonrigid registration is required in order to register the peripheral zone with clinically needed accuracy. The clinical advantage of using nonrigid registration is questionable since the difference between the RMS TREs for rigid and nonrigid intensity-based registration could be considered to be small (0.3 mm) and is statistically significant. If the added clinical value in performing a nonrigid registration is insufficient given the additional time required for this computation, rigid registration alone may be suitable.

An automated neural-fuzzy approach to malignant tumor localization in 2D ultrasonic images of the prostate.

In this paper, a new neural-fuzzy approach is proposed for automated region segmentation in transrectal ultrasound images of the prostate. The goal of region segmentation is to identify suspicious regions in the prostate in order to provide decision support for the diagnosis of prostate cancer. The new automated region segmentation system uses expert knowledge as well as both textural and spatial features in the image to accomplish the segmentation. The textural information is extracted by two recurrent random pulsed neural networks trained by two sets of data (a suspicious tissues' data set and a normal tissues' data set). Spatial information is captured by the atlas-based reference approach and is represented as fuzzy membership functions. The textural and spatial features are synthesized by a fuzzy inference system, which provides a binary classification of the region to be evaluated.

Assessment of image registration accuracy in three-dimensional transrectal ultrasound guided prostate biopsy.

PURPOSE: Prostate biopsy, performed using two-dimensional (2D) transrectal ultrasound (TRUS) guidance, is the clinical standard for a definitive diagnosis of prostate cancer. Histological analysis of the biopsies can reveal cancerous, noncancerous, or suspicious, possibly precancerous, tissue. During subsequent biopsy sessions, noncancerous regions should be avoided, and suspicious regions should be precisely rebiopsied, requiring accurate needle guidance. It is challenging to precisely guide a needle using 2D TRUS due to the limited anatomic information provided, and a three-dimensional (3D) record of biopsy locations for use in subsequent biopsy procedures cannot be collected. Our tracked, 3D TRUS-guided prostate biopsy system provides additional anatomic context and permits a 3D record of biopsies. However, targets determined based on a previous biopsy procedure must be transformed during the procedure to compensate for intraprocedure prostate shifting due to patient motion and prostate deformation due to transducer probe pressure. Thus, registration is a critically important step required to determine these transformations so that correspondence is maintained between the prebiopsied image and the real-time image. Registration must not only be performed accurately, but also quickly, since correction for prostate motion and deformation must be carried out during the biopsy procedure. The authors evaluated the accuracy, variability, and speed of several surface-based and image-based intrasession 3D-to-3D TRUS image registration techniques, for both rigid and nonrigid cases, to find the required transformations. METHODS: Our surface-based rigid and nonrigid registrations of the prostate were performed using the iterative-closest-point algorithm and a thin-plate spline algorithm, respectively. For image-based rigid registration, the authors used a block matching approach, and for nonrigid registration, the authors define the moving image deformation using a regular, 3D grid of B-spline control points. The authors measured the target registration error (TRE) as the postregistration misalignment of 60 manually marked, corresponding intrinsic fiducials. The authors also measured the fiducial localization error (FLE), the effect of segmentation variability, and the effect of fiducial distance from the transducer probe tip. Lastly, the authors performed 3D principal component analysis (PCA) on the x, y, and z components of the TREs to examine the 95% confidence ellipsoids describing the errors for each registration method. RESULTS: Using surface-based registration, the authors found mean TREs of 2.13 +/- 0.80 and 2.09 +/- 0.77 mm for rigid and nonrigid techniques, respectively. Using image-based rigid and non-rigid registration, the authors found mean TREs of 1.74 +/- 0.84 and 1.50 +/- 0.83 mm, respectively. Our FLE was 0.21 mm and did not dominate the overall TRE. However, segmentation variability contributed substantially approximately50%) to the TRE of the surface-based techniques. PCA showed that the 95% confidence ellipsoid encompassing fiducial distances between the source and target registra- tion images was reduced from 3.05 to 0.14 cm3, and 0.05 cm3 for the surface-based and image-based techniques, respectively. The run times for both registration methods were comparable at less than 60 s. CONCLUSIONS: Our results compare favorably with a clinical need for a TRE of less than 2.5 mm, and suggest that image-based registration is superior to surface-based registration for 3D TRUS-guided prostate biopsies, since it does not require segmentation.

Image guided photothermal focal therapy for localized prostate cancer: phase I trial.

PURPOSE: We ascertained the feasibility and safety of image guided targeted photothermal focal therapy for localized prostate cancer. MATERIALS AND METHODS: Twelve patients with biopsy proven low risk prostate cancer underwent interstitial photothermal ablation of the cancer. The area of interest was confirmed and targeted using magnetic resonance imaging. Three-dimensional ultrasound was used to guide a laser to the magnetic resonance to ultrasound fused area of interest. Target ablation was monitored using thermal sensors and real-time Definity contrast enhanced ultrasound. Followup was performed with a combination of magnetic resonance imaging and prostate biopsy. Validated quality of life questionnaires were used to assess the effect on voiding symptoms and erectile function, and adverse events were solicited and recorded. RESULTS: Interstitial photothermal focal therapy was technically feasible to perform. Of the patients 75% were discharged home free from catheter the same day with the remainder discharged home the following day. The treatment created an identifiable hypovascular defect which coincided with the targeted prostatic lesion. There were no perioperative complications and minimal morbidity. All patients who were potent before the procedure maintained potency after the procedure. Continence levels were not compromised. Based on multicore total prostate biopsy at 6 months 67% of patients were free of tumor in the targeted area and 50% were free of disease. CONCLUSIONS: Image guided focal photothermal ablation of low risk and low volume prostate cancer is feasible. Early clinical, histological and magnetic resonance imaging responses suggest that the targeted region can be ablated with minimal adverse effects. It may represent an alternate treatment approach to observation or delayed standard therapy in carefully selected patients. Further trials are required to demonstrate the effectiveness of this treatment concept.

Development and validation of a new guidance device for lateral approach stereotactic breast biopsy.

Stereotactic breast biopsy (SBB) is the gold standard for minimally invasive breast cancer diagnosis. Current systems rely on one of two methods for needle insertion: A vertical approach (perpendicular to the breast compression plate) or a lateral approach (parallel to the compression plate), While the vertical approach is more frequently used, it is not feasible in patients with thin breasts (<3 cm thick after compression) or with superficial lesions. Further, existing SBB guidance hardware provides at most one degree of rotational freedom in the needle trajectory, and as such requires a separate skin incision for each biopsy target. The authors present a new design of lateral guidance device for SBB, which addresses the limitations of the vertical approach and provides improvements over the existing lateral guidance hardware. Specifically, the new device provides (1) an adjustable rigid needle support to minimize needle deflection within the breast and (2) an additional degree of rotational freedom in the needle trajectory, allowing the radiologist to sample multiple targets through a single skin incision. This device was compared to a commercial lateral guidance device in a series of phantom experiments. Needle placement error using each device was measured in agar phantoms for needle insertions at lateral depths of 2 and 5 cm. The biopsy success rate for each device was then estimated by performing biopsy procedures in commercial SBB phantoms. SBB performed with the new lateral guidance device provided reduced needle placement error relative to the commercial lateral guidance device (0.89 +/- 0.22 vs 1.75 +/- 0.35 mm for targets at 2 cm depth; 1.94 +/- 0.20 vs 3.21 +/- 0.31 mm for targets at 5 cm depth). The new lateral guidance device also provided improved biopsy accuracy in SBB procedures compared to the commercial lateral guidance device (100% vs 58% success rate). Finally, experiments were performed to demonstrate that the new device can accurately sample lesions within thin breast phantoms and multiple lesions through a single incision point. This device can be incorporated directly into the clinical SBB procedural workflow, with no additional electrical hardware, software, postprocessing, or image analysis.

Poster - Thurs Eve-02: 3 dimensional ultrasound-guided breast brachytherapy.

Breast cancer is one of Canada's leading causes of death, taking the lives of approximately 5000 people annually. Breast-conserving tumour excision, or lumpectomy followed by radiation therapy is becoming an increasingly common treatment method for smaller tumours. High dose rate (HDR) brachytherapy is a precise form of radiation delivery following surgery involving the delivery of radiation dose through an HDR afterloader attached to catheters inserted into the breast. Currently, a CT scan of the patient is taken to properly reconstruct the tumour and guide catheter insertion. We propose to use our three-dimensional ultrasound (3DUS) scanner as the primary treatment planning device, eliminating the need for a CT scan. This would greatly increase patient comfort along with saving time and money. We have designed and constructed a 3DUS scanner specifically to be used in breast brachytherapy. It attaches to a Kuske breast application kit already used in the clinic. Software to view 3DUS images produced by the device is already being used, and needle guidance software is currently being developed. Laboratory tests on agar phantoms are set to begin shortly to evaluate the precision of the device and perform brachytherapy catheter insertion simulations. When the results of these tests are satisfactory, a full brachytherapy procedure will be performed in Quebec City using the 3DUS scanner.

Poster - Thurs Eve-12: A needle-positioning robot co-registered with volumetric x-ray micro-computed tomography images for minimally-invasive small-animal interventions.

Preclinical research protocols often require the delivery of biological substances to specific targets in small animal disease models. To target biologically relevant locations in mice accurately, the needle positioning error needs to be < 200 µm. If targeting is inaccurate, experimental results can be inconclusive or misleading. We have developed a robotic manipulator that is capable of positioning a needle with a mean error < 100 µm. An apparatus and method were developed for integrating the needle-positioning robot with volumetric micro-computed tomography image guidance for interventions in small animals. Accurate image-to-robot registration is critical for integration as it enables targets identified in the image to be mapped to physical coordinates inside the animal. Registration is accomplished by injecting barium sulphate into needle tracks as the robot withdraws the needle from target points in a tissue-mimicking phantom. Registration accuracy is therefore affected by the positioning error of the robot and is assessed by measuring the point-to-line fiducial and target registration errors (FRE, TRE). Centroid points along cross-sectional slices of the track are determined using region growing segmentation followed by application of a center-of-mass algorithm. The centerline points are registered to needle trajectories in robot coordinates by applying an iterative closest point algorithm between points and lines. Implementing this procedure with four fiducial needle tracks produced a point-to-line FRE and TRE of 246 ± 58 µm and 194 ± 18 µm, respectively. The proposed registration technique produced a TRE < 200 µm, in the presence of robot positioning error, meeting design specification.

Sci-Fri AM: YIS-05: A new guidance device for lateral-approach stereotactic breast biopsy.

Stereotactic breast biopsy (SBB) is the gold standard for noninvasive breast cancer diagnosis. Current systems rely on one of two methods for needle insertion: a top-approach (from above the breast compression plate) or a lateral-approach (parallel to the compression plate). While the top-approach is more commonly used, it is not feasible in patients with thin breasts (less than 2.5 cm thickness after compression), or with superficial lesions. We present a novel design of lateral guidance support for SBB, which addresses these limitations of the top-approach, and provides improvements over existing lateral support hardware. This device incorporates spherical linkages to allow two degrees of rotational freedom in the needle trajectory for increased targeting flexibility, as well as an adjustable rigid needle support to minimize needle deflection within the tissue. Needle placement error in SBB experiments is compared using both the new lateral guidance device and a commercial lateral guidance device in agar phantoms. The effect of elevation angle on needle placement accuracy using the new lateral guidance device is also assessed. Finally, a biopsy accuracy experiment is presented using a certified SBB phantom to compare the new design and the commercial lateral guidance device. In these experiments, SBB performed using the new lateral guidance device results in improved needle placement error and biopsy accuracy, while increasing targeting flexibility and maintaining procedural workflow.

A new lateral guidance device for stereotactic breast biopsy using an add-on unit to an upright mammography system.

Stereotactic breast biopsy (SBB) is the gold standard for noninvasive breast cancer diagnosis. Current systems rely on one of two methods for needle insertion: a vertical-approach (from above the breast compression plate) or a lateral-approach (parallel to the compression plate). While the vertical-approach is more commonly used, it is not feasible in patients with thin breasts (less than 3 cm thickness after compression) or with superficial lesions. We present a novel design of lateral guidance device for SBB which addresses these limitations of the vertical-approach, and provides improvements over existing lateral guidance hardware. This device incorporates spherical linkages to allow two degrees of rotational freedom in the needle trajectory for increased targeting flexibility, as well as an adjustable rigid needle support to minimize needle deflection within the tissue. Needle placement error in SBB experiments is compared using both the new lateral guidance device and a commercial lateral guidance device in agar phantoms. The effect of elevation angle on needle placement accuracy using the new lateral guidance device is also assessed. Finally, a biopsy accuracy experiment is presented using a certified SBB phantom to compare the new design and the commercial lateral guidance device. In these experiments, SBB performed using the new lateral guidance device resulted in improved needle placement error and biopsy accuracy, while increasing targeting flexibility and maintaining procedural workflow.

Stereotactic mammography imaging combined with 3D US imaging for image guided breast biopsy.

Stereotactic X-ray mammography (SM) and ultrasound (US) guidance are both commonly used for breast biopsy. While SM provides three-dimensional (3D) targeting information and US provides real-time guidance, both have limitations. SM is a long and uncomfortable procedure and the US guided procedure is inherently two dimensional (2D), requiring a skilled physician for both safety and accuracy. The authors developed a 3D US-guided biopsy system to be integrated with, and to supplement SM imaging. Their goal is to be able to biopsy a larger percentage of suspicious masses using US, by clarifying ambiguous structures with SM imaging. Features from SM and US guided biopsy were combined, including breast stabilization, a confined needle trajectory, and dual modality imaging. The 3D US guided biopsy system uses a 7.5 MHz breast probe and is mounted on an upright SM machine for preprocedural imaging. Intraprocedural targeting and guidance was achieved with real-time 2D and near real-time 3D US imaging. Postbiopsy 3D US imaging allowed for confirmation that the needle was penetrating the target. The authors evaluated 3D US-guided biopsy accuracy of their system using test phantoms. To use mammographic imaging information, they registered the SM and 3D US coordinate systems. The 3D positions of targets identified in the SM images were determined with a target localization error (TLE) of 0.49 mm. The z component (x-ray tube to image) of the TLE dominated with a TLEz of 0.47 mm. The SM system was then registered to 3D US, with a fiducial registration error (FRE) and target registration error (TRE) of 0.82 and 0.92 mm, respectively. Analysis of the FRE and TRE components showed that these errors were dominated by inaccuracies in the z component with a FREz of 0.76 mm and a TREz of 0.85 mm. A stereotactic mammography and 3D US guided breast biopsy system should include breast compression for stability and safety and dual modality imaging for target localization. The system will provide preprocedural x-ray mammography information in the form of SM imaging along with real-time US imaging for needle guidance to a target. 3D US imaging will also be available for targeting, guidance, and biopsy verification immediately postbiopsy.

3D thoracoscopic ultrasound volume measurement validation in an ex vivo and in vivo porcine model of lung tumours.

The purpose of this study was to validate the accuracy and reliability of volume measurements obtained using three-dimensional (3D) thoracoscopic ultrasound (US) imaging. Artificial "tumours" were created by injecting a liquid agar mixture into spherical moulds of known volume. Once solidified, the "tumours" were implanted into the lung tissue in both a porcine lung sample ex vivo and a surgical porcine model in vivo. 3D US images were created by mechanically rotating the thoracoscopic ultrasound probe about its long axis while the transducer was maintained in close contact with the tissue. Volume measurements were made by one observer using the ultrasound images and a manual-radial segmentation technique and these were compared with the known volumes of the agar. In vitro measurements had average accuracy and precision of 4.76% and 1.77%, respectively; in vivo measurements had average accuracy and precision of 8.18% and 1.75%, respectively. The 3D thoracoscopic ultrasound can be used to accurately and reproducibly measure "tumour" volumes both in vivo and ex vivo.

3D ultrasound analysis of carotid plaque volume and surface morphology.

Morphological characterization of carotid plaques has been used for risk stratification and evaluation of response to therapy, evaluation of new risk factors, genetic research, and for quantifying effects of new anti-atherosclerotic therapies. We developed a 3D US system that allows detailed studies of carotid plaques in 3D. Our software includes 3D reconstruction, viewing, manual and semi-automated segmentation of carotid plaques, and surface morphology analysis to be used for quantitative tracking of plaque changes. We evaluated our plaque quantification software by examining plaque volume measurement accuracy, variability, and plaque surface morphology. We used vascular test phantoms to study segmentation accuracy, and used 48 3D US carotid plaques of patients ranging in size from 13.2 mm(3) to 544.0 mm(3) to study plaque volume measurement variability. We compared results from the semi-automated plaque measurements to the results obtained from manual measurements, which were used as the "gold" standard. We developed a surface plaque morphology quantification technique based on the segmented plaque surface curvature and used it to analyze plaques. Accuracy of plaque volume measurements for the simulated plaques ranged from 4.2% to 1.5% for volumes ranging from 68.5 mm(3) to 286 mm(3). The variability study showed that coefficients of variation in the measurement of plaque volume decreased with increasing plaque size for both inter- (90.8-3.9%) and intra-observer (70.2-3.1%) measurements over the plaque sizes measured. Surface morphology analysis showed that 1 mm ulceration could be quantified and monitored for changes over time. The automated plaque quantification approach showed a little higher intra-observer variability than the manual technique, and its performance was better for segmenting the wall than the lumen. Our results indicate that our approach is sensitive tool and can be used in studies of plaque progression and regression as it relates to atherosclerosis treatment effects and can be used effectively in longitudinal studies for direct measurement carotid plaque volume.