A thorough understanding of the relationship between local hemodynamics and plaque progression has been hindered by an inability to prospectively monitor these factors in vivo in humans. In this study a novel approach for noninvasively reconstructing artery wall thickness and local hemodynamics at the human carotid bifurcation is presented. Three-dimensional (3D) models of the lumen and wall boundaries, from which wall thickness can be measured, were reconstructed from blackblood magnetic resonance imaging (MRI). Along with time-varying inlet/outlet flow rates measured via phase contrast (PC) MRI, the lumen boundary was used as input for computational fluid dynamic (CFD) simulation of the subject-specific flow patterns and wall shear stresses (WSSs). Results from a 59-yearold subject with early, asymptomatic carotid artery disease show good agreement between simulated and measured velocities, and demonstrate a correspondence between wall thickening and low and oscillating shear at the carotid bulb. High shear at the distal internal carotid artery (ICA) was also colocalized with higher WSS; however, a quantitative general relationship between WSS and wall thickness was not found. Similar results were obtained from a 23-year-old normal subject. Wall shear stress (WSS) is widely believed to play a key role in the development and progression of atherosclerotic plaques. Studies comparing human post-mortem distributions of plaque to in vitro fluid dynamic models have perhaps provided the most direct observational evidence for the relationship between WSS and the focal development of atherosclerotic lesions (1-4). The mechanisms by which shear stresses alter endothelial function at the cellular, molecular, and genetic level are also now being elucidated (5). Despite these advances, however, many questions still remain regarding the role of fluid dynamics in the development and progression of atherosclerosis. One reason for this has been the difficulty of identifying and monitoring the relationships between local fluid dynamic factors and plaque development on a subject-specific basis.In principle, both MR and ultrasound imaging can be used to measure wall thickness (a marker for atherosclerotic burden) and blood velocities (from which WSSs are derived) directly. However, difficulties associated with the quantification of blood velocities in regions of complex flow have in the past limited the application of such an "imaging-only" approach to relatively straight sections of the abdominal aorta (6), femoral artery (7), and common carotid artery (8 -10). While these studies were able to confirm an inverse relationship between mean or peak shear and intimal or intima-media thickness, it is not yet possible to use imaging techniques alone to map WSS in the regions of complex flow where plaques are known to localize, such as at the carotid bifurcation. Recent work by Stokholm et al. (11) suggests that WSS from individual slices at the carotid bifurcation itself can be quantified in vivo by sophisticated postprocessing of ph...

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%.

A 3D educational computer model of the larynx has been successfully created and warmly received by medical students.

BackgroundCochlear Duct Length (CDL) has been an important measure for the development and advancement of cochlear implants. Emerging literature has shown CDL can be used in preoperative settings to select the proper sized electrode and develop customized frequency maps. In order to improve post-operative outcomes, and develop new electrode technologies, methods of measuring CDL must be validated to allow usage in the clinic.PurposeThe purpose of this review is to assess the various techniques used to calculate CDL and provide the reader with enough information to make an informed decision on how to conduct future studies measuring the CDL.ResultsThe methods to measure CDL, the modality used to capture images, and the location of the measurement have all changed as technology evolved. With recent popularity and advancement in computed tomography (CT) imaging in place of histologic sections, measurements of CDL have been focused at the lateral wall (LW) instead of the organ of Corti (OC), due to the inability of CT to view intracochlear structures. After analyzing results from methods such as directly measuring CDL from histology, indirectly reconstructing the shape of the cochlea, and determining CDL based on spiral coefficients, it was determined the three dimensional (3D) reconstruction method is the most reliable method to measure CDL. 3D reconstruction provides excellent visualization of the cochlea and avoids errors evident in other methods. Due to the number of varying methods with varying accuracies, certain guidelines must be followed in the future to allow direct comparison of CDL values between studies.ConclusionAfter summarizing and analyzing the interesting history of CDL measurements, the use of standardized guidelines and the importance of CDL for future cochlear implant developments is emphasized for future studies.