Donal B. Downey

Bio: Donal B. Downey is an academic researcher from Robarts Research Institute. The author has contributed to research in topics: 3D ultrasound & Image segmentation. The author has an hindex of 36, co-authored 111 publications receiving 4667 citations. Previous affiliations of Donal B. Downey include American Urological Association & London Health Sciences Centre.

Three-Dimensional Ultrasound Imaging

Abstract: Ultrasound is an inexpensive and widely used imaging modality for the diagnosis and staging of a number of diseases. In the past two decades, it has benefited from major advances in technology and has become an indispensable imaging modality, due to its flexibility and non-invasive character. In the last decade, research investigators and commercial companies have further advanced ultrasound imaging with the development of 3D ultrasound. This new imaging approach is rapidly achieving widespread use with numerous applications. The major reason for the increase in the use of 3D ultrasound is related to the limitations of 2D viewing of 3D anatomy, using conventional ultrasound. This occurs because: (a) Conventional ultrasound images are 2D, yet the anatomy is 3D, hence the diagnostician must integrate multiple images in his mind. This practice is inefficient, and may lead to variability and incorrect diagnoses. (b) The 2D ultrasound image represents a thin plane at some arbitrary angle in the body. It is difficult to localize the image plane and reproduce it at a later time for follow-up studies. In this review article we describe how 3D ultrasound imaging overcomes these limitations. Specifically, we describe the developments of a number of 3D ultrasound imaging systems using mechanical, free-hand and 2D array scanning techniques. Reconstruction and viewing methods of the 3D images are described with specific examples. Since 3D ultrasound is used to quantify the volume of organs and pathology, the sources of errors in the reconstruction techniques as well as formulae relating design specification to geometric errors are provided. Finally, methods to measure organ volume from the 3D ultrasound images and sources of errors are described.

Prostate boundary segmentation from 2D ultrasound images

Abstract: Outlining, or segmenting, the prostate is a very important task in the assignment of appropriate therapy and dose for cancer treatment; however, manual outlining is tedious and time-consuming. In this paper, an algorithm is described for semiautomatic segmentation of the prostate from 2D ultrasound images. The algorithm uses model-based initialization and the efficient discrete dynamic contour. Initialization requires the user to select only four points from which the outline of the prostate is estimated using cubic interpolation functions and shape information. The estimated contour is then deformed automatically to better fit the image. The algorithm can easily segment a wide range of prostate images, and contour editing tools are included to handle more difficult cases. The performance of the algorithm with a single user was compared to manual outlining by a single expert observer. The average distance between semiautomatically and manually outlined boundaries was found to be less than 5 pixels (0.63 mm), and the accuracy and sensitivity to area measurements were both over 90%.

Prostate volume contouring: A 3D analysis of segmentation using 3DTRUS, CT, and MR

Abstract: Purpose: This study evaluated the reproducibility and modality differences of prostate contouring after brachytherapy implant using three-dimensional (3D) transrectal ultrasound (3DTRUS), T2-weighted magnetic resonance (MR), and computed tomography (CT) imaging Methods and Materials: Seven blinded observers contoured 10 patients’ prostates, 30 day postimplant, on 3DTRUS, MR, and CT images to assess interobserver variability Randomized images were contoured twice by each observer We analyzed length and volume measurements and performed a 3D analysis of intra- and intermodality variation Results: Average volume ratios were 116 for CT/MR, 090 for 3DTRUS/MR, and 130 for CT/3DTRUS Overall contouring variability was largest for CT and similar for MR and 3DTRUS The greatest variability of CT contours occurred at the posterior and anterior portions of the midgland On MR, overall variability was smaller, with a maximum in the anterior region On 3DTRUS, high variability occurred in anterior regions of the apex and base, whereas the prostate-rectum interface had the smallest variability The shape of the prostate on MR was rounder, with the base and apex of similar size, whereas CT contours had broad, flat bases narrowing toward the apex The average percent of surface area that was significantly different (95% confidence interval) for CT/MR was 41%; 3DTRUS/MR, 107%; and CT/3DTRUS, 63% The larger variability of CT measurements made significant differences more difficult to detect Conclusions: The contouring of prostates on CT, MR, and 3DTRUS results in systematic differences in the locations of and variability in prostate boundary definition between modalities MR and 3DTRUS display the smallest variability and the closest correspondence

A three-dimensional ultrasound prostate imaging system

Abstract: We have developed a three-dimensional (3D) transrectal ultrasound imaging system, based on using a motorized 5 MHz transducer assembly, rotated under microcomputer control, to collect a series of 100 two-dimensional (2D) images, digitized by a video frame-grabber. These are then reconstructed into a 3D image on a computer workstation, permitting the prostate anatomy to be visualized in three dimensions, and distance and volume measurements to be performed. The accuracy of the distance measurements was assessed with a string test phantom, and that of the volume measurements with balloons of known sizes. Also, the resolution degradation engendered by the reconstruction algorithm was assessed by comparing the full-width at half-maximum (FWHM) of string cross-sectional images in the 3D image to their 2D counterparts. The results show that distance and volume measurements are both accurate to about +/- 1%, and that the reconstruction algorithm increases the mean FWHM by 8 +/- 3% axially and 3 +/- 3% laterally.

Navigation system for cardiac therapies

Abstract: An image guided catheter navigation system for navigating a region of a patient includes an imaging device, a tracking device, a controller, and a display. The imaging device generates images of the region of the patient. The tracking device tracks the location of the catheter in the region of the patient. The controller superimposes an icon representing the catheter onto the images generated from the imaging device based upon the location of the catheter. The display displays the image of the region with the catheter superimposed onto the image at the current location of the catheter.

Pathologic Basis of Disease

Abstract: Pathologic Basis of Diseaseby Stanley L. Robbins is really the fourth edition of hisPathology. Appropriate updating and addition enhance the otherwise identical format, sequence, writing, and illustrations. So many medical students have benefited from this source that it may be the best known general book in the field. I recommend it even more now. Like his former texts, this will be enjoyed for its readability. He clearly lays out a great deal of information. When he includes minutiae, the reasons are clear and one feels that all the material is pertinent. Robbins keeps the whole field in perspective—that is, he does not dwell so long or so heavily on pathologic anatomy or pathogenesis as to tempt the reader to overlook clinical presentation or prognosis. A great strength of the subject of pathology is that it bonds strongly with many other medical sciences and specialties and thus occupies the

Ultrasound image segmentation: a survey

Abstract: This paper reviews ultrasound segmentation methods, in a broad sense, focusing on techniques developed for medical B-mode ultrasound images. First, we present a review of articles by clinical application to highlight the approaches that have been investigated and degree of validation that has been done in different clinical domains. Then, we present a classification of methodology in terms of use of prior information. We conclude by selecting ten papers which have presented original ideas that have demonstrated particular clinical usefulness or potential specific to the ultrasound segmentation problem

EAE/ASE Recommendations for Image Acquisition and Display Using Three-Dimensional Echocardiography

Abstract: CRT : Cardiac resynchronization therapy ECG : Electrocardiographic LV : Left ventricular RV : Right ventricular SDI : Systolic dyssynchrony index TEE : Transesophageal echocardiographic 3D : Three-dimensional 3DE : Three-dimensional echocardiographic TTE : Transthoracic echocardiographic TV : Tricuspid valve 2D : Two-dimensional Three-dimensional (3D) echocardiographic (3DE) imaging represents a major innovation in cardiovascular ultrasound. Advancements in computer and transducer technologies permit real-time 3DE acquisition and presentation of cardiac structures from any spatial point of view. The usefulness of 3D echocardiography has been demonstrated in (1) the evaluation of cardiac chamber volumes and mass, which avoids geometric assumptions; (2) the assessment of regional left ventricular (LV) wall motion and quantification of systolic dyssynchrony; (3) presentation of realistic views of heart valves; (4) volumetric evaluation of regurgitant lesions and shunts with 3DE color Doppler imaging; and (5) 3DE stress imaging. However, for 3D echocardiography to be implemented in routine clinical practice, a full understanding of its technical principles and a systematic approach to image acquisition and analysis are required. The main goal of this document is to provide a practical guide on how to acquire, analyze, and display the various cardiac structures using 3D echocardiography, as well as limitations of the technique. In addition, this document describes the current and potential clinical applications of 3D echocardiography along with their strengths and weaknesses. ### a. Fully Sampled Matrix-Array Transducers An important milestone in the history of real-time 3D echocardiography was reached shortly after the year 2000, with the development of fully sampled matrix-array transducers. These transducers provided excellent real-time imaging of the beating heart in three dimensions and required significant technological developments in both hardware and software, including transducer design, microelectronic techniques, and computing. Currently, 3DE matrix-array transducers are composed of nearly 3,000 piezoelectric elements with operating frequencies ranging from 2 to 4 MHz and from 5 to 7 MHz for transthoracic echocardiographic (TTE) and transesophageal echocardiographic (TEE) imaging, respectively. These piezoelectric elements are arranged in a matrix configuration within the transducer and require a large number of digital channels for these fully sampled elements to be connected. To reduce both …