A. Fenster - Academia.edu (original) (raw)

Papers by A. Fenster

Journal of Magnetic Resonance Imaging, 2012

Purpose: To present and evaluate a method for registration of whole-mount prostate digital histol... more Purpose: To present and evaluate a method for registration of whole-mount prostate digital histology images to ex vivo magnetic resonance (MR) images. Materials and Methods: Nine radical prostatectomy specimens were marked with 10 strand-shaped fiducial markers per specimen, imaged with T1-and T2-weighted 3T MRI protocols, sliced at 4.4-mm intervals, processed for whole-mount histology, and the resulting histological sections (3-5 per specimen, 34 in total) were digitized. The correspondence between fiducial markers on histology and MR images yielded an initial registration, which was refined by a local optimization technique, yielding the least-squares best-fit affine transformation between corresponding fiducial points on histology and MR images. Accuracy was quantified as the postregistration 3D distance between landmarks (3-7 per section, 184 in total) on histology and MR images, and compared to a previous stateof-the-art registration method. Results: The proposed method and previous method had mean (SD) target registration errors of 0.71 (0.38) mm and 1.21 (0.74) mm, respectively, requiring 3 and 11 hours of processing time, respectively. Conclusion: The proposed method registers digital histology to prostate MR images, yielding 70% reduced processing time and mean accuracy sufficient to achieve 85% overlap on histology and ex vivo MR images for a 0.2 cc spherical tumor.

Physics in Medicine and Biology, 2004

Medical Physics, 1983

Accurate high-resolution x-ray spectral distributions can be obtained with an intrinsic germanium... more Accurate high-resolution x-ray spectral distributions can be obtained with an intrinsic germanium crystal. This technique is difficult to implement since it requires expensive, complicated, and bulky equipment. If energy resolution requirements are relaxed, then the above drawbacks can be overcome and an x-ray spectrometer that is small, inexpensive could be built. A technique that meets these requirements is described here. X-ray spectra with about 7-keV resolution can be achieved by obtaining transmission measurements through a number of different K-edge filters. Using these measurements, a system of equations is set up and solved giving the required spectral distribution. The technique has been tested using 80, 100, and 120-kVcp x-ray beams with total filtrations of 3.78, 5.78, 9.06 mm A1, and 3.78 mm A1 + 0.137 mm Ho. The results show that the calculated spectra closely resemble tabulated spectra. The errors ranged from 3% to 13%. The half-value layers (HVL) were also calculated and compared to the HVL obtained from tabulated spectra and were found to differ by about 7%.

Medical Physics, 1991

In the analysis of x-ray system performance, the log-signal function, or negative logarithm of th... more In the analysis of x-ray system performance, the log-signal function, or negative logarithm of the relative detector signal, and the analogously defined log-variance function, are of central importance. These are smooth, monotonic functions of object thickness, which are nonlinear for nonmonoenergetic x-ray source spectra. If we assume a dual-energy decomposition of the object into two basis materials, then they can be written as analytic functions f(x,y) and f*(x,y), respectively, of the component thicknesses (x,y) of the object. In this paper, we analytically develop the Taylor series of these functions, prove that they converge everywhere, and parametrize their coefficients via suitable central spectral moments of the basis-material attenuation coefficients. We then show how the lower-order moments can be used to construct, in closed form, smooth, monotonic, second-order (conic) surface functions which closely approximate f(x,y) and f*(x,y) over the entire feasible domain. A simplified construction, based on using appropriate asymptotic values of the basis-material attenuation coefficients to match the asymptotic behavior of these functions, is also given. The inclusion of image components with K-edge absorption spectra, such as iodine, is done without effort. Extension of the results to the construction of similar (virtually exact) third-order (cubic) surface approximations is straightforward. As an illustration of the broad applicability of this approach, we extend our analysis to the construction of similar approximations to the inverse (decomposition) functions for an arbitrary dual-energy system, and investigate their numerical accuracy for a model dual-kVp system. We conclude that this extended analysis provides an accurate description of the system behavior in terms of a small number of physically meaningful parameters. This parametrization permits greater physical insight into the system behavior, while at the same time simplifying its mathematical description, and similarly facilitates the analysis of various measures of imaging performance via either analytic or numerical methods.

Medical Physics, 2013

ABSTRACT Purpose: We present a simple, fast and robust method to optimize both the number and pos... more ABSTRACT Purpose: We present a simple, fast and robust method to optimize both the number and position of catheters in interstitial high dose rate (HDR) brachytherapy, using a modified version of the Centroidal Voronoi Tessellations algorithm. Methods: 8 HDR clinical cases were chosen randomly for both prostate and breast to test our method. The dose distributions were obtained using a research version of IPSA. Clinically relevant dosimetric parameters were computed to evaluate our method and test the robustness. For the prostate, plans generated from our method were compared to the clinical cases with 17 catheters. The efficiency of the algorithm was also tested with breast cases. The robustness of the method to implantation error was evaluated using 100 iterations and an error of 1, 2, 3, or 5 mm to each catheter of the plan. Results: A better or equal prostate V100 was obtained with as few as 12 catheters when compared with the clinical case. Plans with 9 or less catheters would not be clinically acceptable. Plans with 17 catheters were better than the clinical plans with the same number of catheters. The computation time to obtain 10 complete treatment plans ranging from 9 to 18 catheters, with the corresponding dosimetric indices, was 90 s. For the breast, on average, the RTOG recommendations would be satisfied with 12 catheters. Plans with 9 or less catheters would not be clinically acceptable in terms of V100, DHI and D90. Implantation errors up to 3 mm were acceptable. Conclusion: We have devised a simple, fast, robust and efficient method to optimize the number and position of catheters in HDR brachytherapy. Ultimately, this catheter optimization algorithm could be coupled with a 3D ultrasound system to allow real‐time guidance and planning for any interstitial brachytherapy sites. Funding support: CIHR and NSERC

Medical Imaging 2014: Digital Pathology, 2014

ABSTRACT Purpose: Multiparametric magnetic resonance imaging (MPMRI) supports detection and stagi... more ABSTRACT Purpose: Multiparametric magnetic resonance imaging (MPMRI) supports detection and staging of prostate cancer, but the image characteristics needed for tumor boundary delineation to support focal therapy have not been widely investigated. We quantified the detectability (image contrast between tumor and non-cancerous contralateral tissue) and the localizability (image contrast between tumor and non-cancerous neighboring tissue) of Gleason score 7 (GS7) peripheral zone (PZ) tumors on MPMRI using tumor contours mapped from histology using accurate 2D-3D registration. Methods: MPMRI [comprising T2-weighted (T2W), dynamic-contrast-enhanced (DCE), apparent diffusion coefficient (ADC) and contrast transfer coefficient images] and post-prostatectomy digitized histology images were acquired for 6 subjects. Histology contouring and grading (approved by a genitourinary pathologist) identified 7 GS7 PZ tumors. Contours were mapped to MPMRI images using semi-automated registration algorithms (combined target registration error: 2 mm). For each focus, three measurements of mean +/- standard deviation of image intensity were taken on each image: tumor tissue (mT+/-sT), non-cancerous PZ tissue < 5 mm from the tumor (mN+/-sN), and non-cancerous contralateral PZ tissue (mC+/-sC). Detectability [D, defined as mT-mC normalized by sT and sC added in quadrature] and localizability [L, defined as mT-mN normalized by sT and sN added in quadrature] were quantified for each focus on each image. Results: T2W images showed the strongest detectability, although detectability |D|>=1 was observed on either ADC or DCE images, or both, for all foci. Localizability on all modalities was variable; however, ADC images showed localizability |L|>=1 for 3 foci. Conclusions: Delineation of GS7 PZ tumors on individual MPMRI images faces challenges; however, images may contain complementary information, suggesting a role for fusion of information across MPMRI images for delineation.

Radiology, 2012

To develop and evaluate a technique for the registration of in vivo prostate magnetic resonance (... more To develop and evaluate a technique for the registration of in vivo prostate magnetic resonance (MR) images to digital histopathologic images by using image-guided specimen slicing based on strand-shaped fiducial markers relating specimen imaging to histopathologic examination.

CCECE 2003 - Canadian Conference on Electrical and Computer Engineering. Toward a Caring and Humane Technology (Cat. No.03CH37436)

Due to the quality of the ultrasound image, it is very difficult to develop a computerized method... more Due to the quality of the ultrasound image, it is very difficult to develop a computerized method for defining the boundary of an object in this type of image. This paper focuses on developing a semiautomatic method for detecting the boundary of a prostate. The algorithm is based on Mallat's (1992) multiscale edge detection method and the discrete dynamic contour

Clinical & Investigative Medicine, 2007

Introduction: Transrectal ultrasound (TRUS) prostate biopsy (Bx) is currently confined to 2D info... more Introduction: Transrectal ultrasound (TRUS) prostate biopsy (Bx) is currently confined to 2D information to both target and record 3D Bx locations. Accurate placement of Bx needles cannot be verified without 3D information, and recording Bx sites in 2D does not provide sufficient information to accurately guide the high incidence of repeat Bx. We have designed a 3D TRUS prostate Bx system that augments the current 2D TRUS system and provides tools for biopsy-planning, needle guidance, and recording of the biopsy core locations entirely in 3D. Methods: Our Bx system displays a 3D model of the patient’s prostate, which is generated intra-procedure from a collection of 2D TRUS images, representative of the particular prostate shape. Bx targets are selected, needle guidance is facilitated, and 3D Bx sites are recorded within the 3D context of the prostate model. The complete 3D Bx system was validated, in vitro, by performing standard ten-core Bx on anatomical phantoms of two patient’s ...

Proceedings of the 1995 Fourteenth Southern Biomedical Engineering Conference, 1995

Angioplasty is a common and successful technique for reopening stenosed arteries to blood flow. I... more Angioplasty is a common and successful technique for reopening stenosed arteries to blood flow. In spite of this achievement, a large number of patients restenose the site of angioplasty within only 6 months of the procedure. Clearly, the patient's response to angioplasty is not consistent but instead, appears to be unpredictable. Although angioplasty is often chosen over surgery, the mechanism

Physiological Measurement, 2002

Atherosclerosis represents a significant cause of morbidity and mortality in the western world. M... more Atherosclerosis represents a significant cause of morbidity and mortality in the western world. Manifestations of atherosclerotic disease among the elderly include the development of raised lesions that often include calcified regions with material properties similar to bone. There is little information available about the amount and distribution of these calcified plaques within the human aorta, partly due to the difficulty in obtaining this information during in vivo studies. We report the results of a cadaveric investigation of thoracic aortic wall thickness, diameter and calcium content. A non-destructive x-ray imaging technique was used to obtain two-dimensional maps of total thickness and mineral content in excised thoracic aortic specimens. In a study of 39 individuals (23 male and 16 female, aged 20-92 years) we report a significant non-linear correlation between calcium burden and age, with calcium deposition most commonly occurring proximal to the ostia of major branching vessels. We also found a significant linear correlation between age and both total aortic wall thickness and aortic diameter. An improved understanding of the pathological changes in the ageing thoracic aorta may be useful in the development of strategies to reduce the undesirable vessel calcification associated with atherosclerosis.

Medical Imaging IV: Image Formation, 1990

ABSTRACT

Medical Imaging 2014: Image-Guided Procedures, Robotic Interventions, and Modeling, 2014

ABSTRACT Dilated lateral ventricles in neonates can be due to many different causes, such as brai... more ABSTRACT Dilated lateral ventricles in neonates can be due to many different causes, such as brain loss, or congenital malformation; however, the main cause is hydrocephalus, which is the accumulation of fluid within the ventricular system. Hydrocephalus is causing a raised in Such enlargement can raise intracranial pressure resulting in secondary brain damage, and up to 25% of patients with severely enlarged ventricles have epilepsy in later life. Ventricle enlargement is clinically monitored using 2D US through the fontanels. The sensitivity of 2D US to dilation is poor because it cannot provide accurate measurements of irregular volumes such as the ventricles, so most clinical evaluations are of a qualitative nature. We developed a 3DUS system to image the cerebral ventricles of neonates within the confines of incubators and can be easily translated to more open environments. Ventricle volumes can be segmented from these images giving a quantitative volumetric measurement of ventricle enlargement without moving the patient into an imaging facility. In this paper, we report on in vivo validation studies 1) comparing 3DUS ventricle volumes before and after clinically necessary interventions removing CSF and 2) comparing 3DUS ventricle volumes to those from MRI. Post-intervention ventricle volumes were less than pre-intervention measurements for all patients and all interventions. We found high correlations (R = 0.97) between the difference in ventricle volume and the reported removed CSF with the slope not sig different than 1 (p < 0.05). Comparisons between ventricle volumes from 3DUS and MR images taken 4 (±3.8) days of each other failed to show significant difference (p=0.44) between 3DUS and MRI through paired t-test.

Physiological Measurement, 1993

Medical Imaging 1993: Image Processing, 1993

ABSTRACT

Medical Imaging 2014: Image-Guided Procedures, Robotic Interventions, and Modeling, 2014

ABSTRACT Two dimensional (2D) transrectal ultrasound (TRUS) guided prostate biopsy is the standar... more ABSTRACT Two dimensional (2D) transrectal ultrasound (TRUS) guided prostate biopsy is the standard approach for definitive diagnosis of prostate cancer (PCa). However, due to the lack of image contrast of prostate tumors needed to clearly visualize early-stage PCa, prostate biopsy often results in false negatives, requiring repeat biopsies. Magnetic Resonance Imaging (MRI) has been considered to be a promising imaging modality for noninvasive identification of PCa, since it can provide a high sensitivity and specificity for the detection of early stage PCa. Our main objective is to develop and validate a registration method of 3D MR-TRUS images, allowing generation of volumetric 3D maps of targets identified in 3D MR images to be biopsied using 3D TRUS images. Our registration method first makes use of an initial rigid registration of 3D MR images to 3D TRUS images using 6 manually placed approximately corresponding landmarks in each image. Following the manual initialization, two prostate surfaces are segmented from 3D MR and TRUS images and then non-rigidly registered using a thin-plate spline (TPS) algorithm. The registration accuracy was evaluated using 4 patient images by measuring target registration error (TRE) of manually identified corresponding intrinsic fiducials (calcifications and/or cysts) in the prostates. Experimental results show that the proposed method yielded an overall mean TRE of 2.05 mm, which is favorably comparable to a clinical requirement for an error of less than 2.5 mm.

SPIE Proceedings, 2011

ABSTRACT Three-dimensional (3D) manual segmentation of lung tumours is observer-dependent and tim... more ABSTRACT Three-dimensional (3D) manual segmentation of lung tumours is observer-dependent and time consuming, which are major limitations for use in clinical trials. In this paper we present a semi-automated D segmentation method, which is more time-efficient and less operator dependent than manual segmentation. We developed a semi-automated algorithm to segment lung tumours on chest computed tomography (CT) images using shape constrained multi-thresholding (SCMT) and sparse field active model (SFAM) techniques. For each 2D slice of CT tumour image, an initial contour was generated using SCMT. This initial contour was then deformed using SFAM. Seven energies were utilized in the SFAM technique to control the deformation namely: global region, local region, curvature, edge information, smoothness, anchor, and partial volume. The proposed algorithm was tested with 70 CT tumour slices (19 well-defined tumours (WD) located centrally in the lung parenchyma without significant vasculature and 51 vascularized or juxtapleural tumours (VJ)). Our results showed that the initial contour generated by the SCMT technique was sufficient to segment the well-defined (WD) tumours without any deformation. However, the deformation using SFAM was required to segment vascularized or juxtapleural (VJ) tumours. The results of the proposed segmentation algorithm were evaluated by comparing them to manual segmentation using the dice coefficient (DC). The average DC was 96.3+/-1.1% and 95.2+/-1.6% for WD and VJ tumour images respectively. The average DC obtained for the entire data set was 95.5+/-1.6%, which shows that the proposed algorithm can accurately segment lung tumours and can be utilized for monitoring tumours response to treatment.

IEEE 1992 Ultrasonics Symposium Proceedings

Intravascular ultrasound imaging systems are effective in identifying and characterizing occlusiv... more Intravascular ultrasound imaging systems are effective in identifying and characterizing occlusive arterial disease. In order to investigate changes in vessel wall elasticity due to atherosclerosis, a real-time, high-frequency intravascular ultrasound imaging system has been developed for the study of excised artery sections in vitro. The system consists of a miniature ultrasound probe constructed from a 42-MHz lead zirconate titanate (PZT)

Journal of Magnetic Resonance Imaging, 2012

Purpose: To present and evaluate a method for registration of whole-mount prostate digital histol... more Purpose: To present and evaluate a method for registration of whole-mount prostate digital histology images to ex vivo magnetic resonance (MR) images. Materials and Methods: Nine radical prostatectomy specimens were marked with 10 strand-shaped fiducial markers per specimen, imaged with T1-and T2-weighted 3T MRI protocols, sliced at 4.4-mm intervals, processed for whole-mount histology, and the resulting histological sections (3-5 per specimen, 34 in total) were digitized. The correspondence between fiducial markers on histology and MR images yielded an initial registration, which was refined by a local optimization technique, yielding the least-squares best-fit affine transformation between corresponding fiducial points on histology and MR images. Accuracy was quantified as the postregistration 3D distance between landmarks (3-7 per section, 184 in total) on histology and MR images, and compared to a previous stateof-the-art registration method. Results: The proposed method and previous method had mean (SD) target registration errors of 0.71 (0.38) mm and 1.21 (0.74) mm, respectively, requiring 3 and 11 hours of processing time, respectively. Conclusion: The proposed method registers digital histology to prostate MR images, yielding 70% reduced processing time and mean accuracy sufficient to achieve 85% overlap on histology and ex vivo MR images for a 0.2 cc spherical tumor.

Physics in Medicine and Biology, 2004

Medical Physics, 1983

Accurate high-resolution x-ray spectral distributions can be obtained with an intrinsic germanium... more Accurate high-resolution x-ray spectral distributions can be obtained with an intrinsic germanium crystal. This technique is difficult to implement since it requires expensive, complicated, and bulky equipment. If energy resolution requirements are relaxed, then the above drawbacks can be overcome and an x-ray spectrometer that is small, inexpensive could be built. A technique that meets these requirements is described here. X-ray spectra with about 7-keV resolution can be achieved by obtaining transmission measurements through a number of different K-edge filters. Using these measurements, a system of equations is set up and solved giving the required spectral distribution. The technique has been tested using 80, 100, and 120-kVcp x-ray beams with total filtrations of 3.78, 5.78, 9.06 mm A1, and 3.78 mm A1 + 0.137 mm Ho. The results show that the calculated spectra closely resemble tabulated spectra. The errors ranged from 3% to 13%. The half-value layers (HVL) were also calculated and compared to the HVL obtained from tabulated spectra and were found to differ by about 7%.

Medical Physics, 1991

In the analysis of x-ray system performance, the log-signal function, or negative logarithm of th... more In the analysis of x-ray system performance, the log-signal function, or negative logarithm of the relative detector signal, and the analogously defined log-variance function, are of central importance. These are smooth, monotonic functions of object thickness, which are nonlinear for nonmonoenergetic x-ray source spectra. If we assume a dual-energy decomposition of the object into two basis materials, then they can be written as analytic functions f(x,y) and f*(x,y), respectively, of the component thicknesses (x,y) of the object. In this paper, we analytically develop the Taylor series of these functions, prove that they converge everywhere, and parametrize their coefficients via suitable central spectral moments of the basis-material attenuation coefficients. We then show how the lower-order moments can be used to construct, in closed form, smooth, monotonic, second-order (conic) surface functions which closely approximate f(x,y) and f*(x,y) over the entire feasible domain. A simplified construction, based on using appropriate asymptotic values of the basis-material attenuation coefficients to match the asymptotic behavior of these functions, is also given. The inclusion of image components with K-edge absorption spectra, such as iodine, is done without effort. Extension of the results to the construction of similar (virtually exact) third-order (cubic) surface approximations is straightforward. As an illustration of the broad applicability of this approach, we extend our analysis to the construction of similar approximations to the inverse (decomposition) functions for an arbitrary dual-energy system, and investigate their numerical accuracy for a model dual-kVp system. We conclude that this extended analysis provides an accurate description of the system behavior in terms of a small number of physically meaningful parameters. This parametrization permits greater physical insight into the system behavior, while at the same time simplifying its mathematical description, and similarly facilitates the analysis of various measures of imaging performance via either analytic or numerical methods.

Medical Physics, 2013

ABSTRACT Purpose: We present a simple, fast and robust method to optimize both the number and pos... more ABSTRACT Purpose: We present a simple, fast and robust method to optimize both the number and position of catheters in interstitial high dose rate (HDR) brachytherapy, using a modified version of the Centroidal Voronoi Tessellations algorithm. Methods: 8 HDR clinical cases were chosen randomly for both prostate and breast to test our method. The dose distributions were obtained using a research version of IPSA. Clinically relevant dosimetric parameters were computed to evaluate our method and test the robustness. For the prostate, plans generated from our method were compared to the clinical cases with 17 catheters. The efficiency of the algorithm was also tested with breast cases. The robustness of the method to implantation error was evaluated using 100 iterations and an error of 1, 2, 3, or 5 mm to each catheter of the plan. Results: A better or equal prostate V100 was obtained with as few as 12 catheters when compared with the clinical case. Plans with 9 or less catheters would not be clinically acceptable. Plans with 17 catheters were better than the clinical plans with the same number of catheters. The computation time to obtain 10 complete treatment plans ranging from 9 to 18 catheters, with the corresponding dosimetric indices, was 90 s. For the breast, on average, the RTOG recommendations would be satisfied with 12 catheters. Plans with 9 or less catheters would not be clinically acceptable in terms of V100, DHI and D90. Implantation errors up to 3 mm were acceptable. Conclusion: We have devised a simple, fast, robust and efficient method to optimize the number and position of catheters in HDR brachytherapy. Ultimately, this catheter optimization algorithm could be coupled with a 3D ultrasound system to allow real‐time guidance and planning for any interstitial brachytherapy sites. Funding support: CIHR and NSERC

Medical Imaging 2014: Digital Pathology, 2014

ABSTRACT Purpose: Multiparametric magnetic resonance imaging (MPMRI) supports detection and stagi... more ABSTRACT Purpose: Multiparametric magnetic resonance imaging (MPMRI) supports detection and staging of prostate cancer, but the image characteristics needed for tumor boundary delineation to support focal therapy have not been widely investigated. We quantified the detectability (image contrast between tumor and non-cancerous contralateral tissue) and the localizability (image contrast between tumor and non-cancerous neighboring tissue) of Gleason score 7 (GS7) peripheral zone (PZ) tumors on MPMRI using tumor contours mapped from histology using accurate 2D-3D registration. Methods: MPMRI [comprising T2-weighted (T2W), dynamic-contrast-enhanced (DCE), apparent diffusion coefficient (ADC) and contrast transfer coefficient images] and post-prostatectomy digitized histology images were acquired for 6 subjects. Histology contouring and grading (approved by a genitourinary pathologist) identified 7 GS7 PZ tumors. Contours were mapped to MPMRI images using semi-automated registration algorithms (combined target registration error: 2 mm). For each focus, three measurements of mean +/- standard deviation of image intensity were taken on each image: tumor tissue (mT+/-sT), non-cancerous PZ tissue < 5 mm from the tumor (mN+/-sN), and non-cancerous contralateral PZ tissue (mC+/-sC). Detectability [D, defined as mT-mC normalized by sT and sC added in quadrature] and localizability [L, defined as mT-mN normalized by sT and sN added in quadrature] were quantified for each focus on each image. Results: T2W images showed the strongest detectability, although detectability |D|>=1 was observed on either ADC or DCE images, or both, for all foci. Localizability on all modalities was variable; however, ADC images showed localizability |L|>=1 for 3 foci. Conclusions: Delineation of GS7 PZ tumors on individual MPMRI images faces challenges; however, images may contain complementary information, suggesting a role for fusion of information across MPMRI images for delineation.

Radiology, 2012

To develop and evaluate a technique for the registration of in vivo prostate magnetic resonance (... more To develop and evaluate a technique for the registration of in vivo prostate magnetic resonance (MR) images to digital histopathologic images by using image-guided specimen slicing based on strand-shaped fiducial markers relating specimen imaging to histopathologic examination.

CCECE 2003 - Canadian Conference on Electrical and Computer Engineering. Toward a Caring and Humane Technology (Cat. No.03CH37436)

Due to the quality of the ultrasound image, it is very difficult to develop a computerized method... more Due to the quality of the ultrasound image, it is very difficult to develop a computerized method for defining the boundary of an object in this type of image. This paper focuses on developing a semiautomatic method for detecting the boundary of a prostate. The algorithm is based on Mallat's (1992) multiscale edge detection method and the discrete dynamic contour

Clinical & Investigative Medicine, 2007

Introduction: Transrectal ultrasound (TRUS) prostate biopsy (Bx) is currently confined to 2D info... more Introduction: Transrectal ultrasound (TRUS) prostate biopsy (Bx) is currently confined to 2D information to both target and record 3D Bx locations. Accurate placement of Bx needles cannot be verified without 3D information, and recording Bx sites in 2D does not provide sufficient information to accurately guide the high incidence of repeat Bx. We have designed a 3D TRUS prostate Bx system that augments the current 2D TRUS system and provides tools for biopsy-planning, needle guidance, and recording of the biopsy core locations entirely in 3D. Methods: Our Bx system displays a 3D model of the patient’s prostate, which is generated intra-procedure from a collection of 2D TRUS images, representative of the particular prostate shape. Bx targets are selected, needle guidance is facilitated, and 3D Bx sites are recorded within the 3D context of the prostate model. The complete 3D Bx system was validated, in vitro, by performing standard ten-core Bx on anatomical phantoms of two patient’s ...

Proceedings of the 1995 Fourteenth Southern Biomedical Engineering Conference, 1995

Angioplasty is a common and successful technique for reopening stenosed arteries to blood flow. I... more Angioplasty is a common and successful technique for reopening stenosed arteries to blood flow. In spite of this achievement, a large number of patients restenose the site of angioplasty within only 6 months of the procedure. Clearly, the patient's response to angioplasty is not consistent but instead, appears to be unpredictable. Although angioplasty is often chosen over surgery, the mechanism

Physiological Measurement, 2002

Atherosclerosis represents a significant cause of morbidity and mortality in the western world. M... more Atherosclerosis represents a significant cause of morbidity and mortality in the western world. Manifestations of atherosclerotic disease among the elderly include the development of raised lesions that often include calcified regions with material properties similar to bone. There is little information available about the amount and distribution of these calcified plaques within the human aorta, partly due to the difficulty in obtaining this information during in vivo studies. We report the results of a cadaveric investigation of thoracic aortic wall thickness, diameter and calcium content. A non-destructive x-ray imaging technique was used to obtain two-dimensional maps of total thickness and mineral content in excised thoracic aortic specimens. In a study of 39 individuals (23 male and 16 female, aged 20-92 years) we report a significant non-linear correlation between calcium burden and age, with calcium deposition most commonly occurring proximal to the ostia of major branching vessels. We also found a significant linear correlation between age and both total aortic wall thickness and aortic diameter. An improved understanding of the pathological changes in the ageing thoracic aorta may be useful in the development of strategies to reduce the undesirable vessel calcification associated with atherosclerosis.

Medical Imaging IV: Image Formation, 1990

ABSTRACT

Medical Imaging 2014: Image-Guided Procedures, Robotic Interventions, and Modeling, 2014

ABSTRACT Dilated lateral ventricles in neonates can be due to many different causes, such as brai... more ABSTRACT Dilated lateral ventricles in neonates can be due to many different causes, such as brain loss, or congenital malformation; however, the main cause is hydrocephalus, which is the accumulation of fluid within the ventricular system. Hydrocephalus is causing a raised in Such enlargement can raise intracranial pressure resulting in secondary brain damage, and up to 25% of patients with severely enlarged ventricles have epilepsy in later life. Ventricle enlargement is clinically monitored using 2D US through the fontanels. The sensitivity of 2D US to dilation is poor because it cannot provide accurate measurements of irregular volumes such as the ventricles, so most clinical evaluations are of a qualitative nature. We developed a 3DUS system to image the cerebral ventricles of neonates within the confines of incubators and can be easily translated to more open environments. Ventricle volumes can be segmented from these images giving a quantitative volumetric measurement of ventricle enlargement without moving the patient into an imaging facility. In this paper, we report on in vivo validation studies 1) comparing 3DUS ventricle volumes before and after clinically necessary interventions removing CSF and 2) comparing 3DUS ventricle volumes to those from MRI. Post-intervention ventricle volumes were less than pre-intervention measurements for all patients and all interventions. We found high correlations (R = 0.97) between the difference in ventricle volume and the reported removed CSF with the slope not sig different than 1 (p < 0.05). Comparisons between ventricle volumes from 3DUS and MR images taken 4 (±3.8) days of each other failed to show significant difference (p=0.44) between 3DUS and MRI through paired t-test.

Physiological Measurement, 1993

Medical Imaging 1993: Image Processing, 1993

ABSTRACT

Medical Imaging 2014: Image-Guided Procedures, Robotic Interventions, and Modeling, 2014

ABSTRACT Two dimensional (2D) transrectal ultrasound (TRUS) guided prostate biopsy is the standar... more ABSTRACT Two dimensional (2D) transrectal ultrasound (TRUS) guided prostate biopsy is the standard approach for definitive diagnosis of prostate cancer (PCa). However, due to the lack of image contrast of prostate tumors needed to clearly visualize early-stage PCa, prostate biopsy often results in false negatives, requiring repeat biopsies. Magnetic Resonance Imaging (MRI) has been considered to be a promising imaging modality for noninvasive identification of PCa, since it can provide a high sensitivity and specificity for the detection of early stage PCa. Our main objective is to develop and validate a registration method of 3D MR-TRUS images, allowing generation of volumetric 3D maps of targets identified in 3D MR images to be biopsied using 3D TRUS images. Our registration method first makes use of an initial rigid registration of 3D MR images to 3D TRUS images using 6 manually placed approximately corresponding landmarks in each image. Following the manual initialization, two prostate surfaces are segmented from 3D MR and TRUS images and then non-rigidly registered using a thin-plate spline (TPS) algorithm. The registration accuracy was evaluated using 4 patient images by measuring target registration error (TRE) of manually identified corresponding intrinsic fiducials (calcifications and/or cysts) in the prostates. Experimental results show that the proposed method yielded an overall mean TRE of 2.05 mm, which is favorably comparable to a clinical requirement for an error of less than 2.5 mm.

SPIE Proceedings, 2011

ABSTRACT Three-dimensional (3D) manual segmentation of lung tumours is observer-dependent and tim... more ABSTRACT Three-dimensional (3D) manual segmentation of lung tumours is observer-dependent and time consuming, which are major limitations for use in clinical trials. In this paper we present a semi-automated D segmentation method, which is more time-efficient and less operator dependent than manual segmentation. We developed a semi-automated algorithm to segment lung tumours on chest computed tomography (CT) images using shape constrained multi-thresholding (SCMT) and sparse field active model (SFAM) techniques. For each 2D slice of CT tumour image, an initial contour was generated using SCMT. This initial contour was then deformed using SFAM. Seven energies were utilized in the SFAM technique to control the deformation namely: global region, local region, curvature, edge information, smoothness, anchor, and partial volume. The proposed algorithm was tested with 70 CT tumour slices (19 well-defined tumours (WD) located centrally in the lung parenchyma without significant vasculature and 51 vascularized or juxtapleural tumours (VJ)). Our results showed that the initial contour generated by the SCMT technique was sufficient to segment the well-defined (WD) tumours without any deformation. However, the deformation using SFAM was required to segment vascularized or juxtapleural (VJ) tumours. The results of the proposed segmentation algorithm were evaluated by comparing them to manual segmentation using the dice coefficient (DC). The average DC was 96.3+/-1.1% and 95.2+/-1.6% for WD and VJ tumour images respectively. The average DC obtained for the entire data set was 95.5+/-1.6%, which shows that the proposed algorithm can accurately segment lung tumours and can be utilized for monitoring tumours response to treatment.

IEEE 1992 Ultrasonics Symposium Proceedings

Intravascular ultrasound imaging systems are effective in identifying and characterizing occlusiv... more Intravascular ultrasound imaging systems are effective in identifying and characterizing occlusive arterial disease. In order to investigate changes in vessel wall elasticity due to atherosclerosis, a real-time, high-frequency intravascular ultrasound imaging system has been developed for the study of excised artery sections in vitro. The system consists of a miniature ultrasound probe constructed from a 42-MHz lead zirconate titanate (PZT)