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Show 205 THE UNIVERSITY OF UTAH Background. Atrial fibrillation (AF), the most common cardiac arrhythmia, increases a patient's risk for stroke five fold. The shape and structure of the left atrial appendage (LAA) have been proposed as possible factors influencing the occurrence of stroke in patients with AF. Therefore, we describe an image processing method utilizing magnetic resonance angiography (MRA) to generate three-dimensional models of the LAA, from which volume and shape can be assessed and correlated with stroke occurrence. Methods. Twenty-eight cardiac MRA scans (14 patients with history of stroke) were manually segmented to delineate the left atrium (LA) from the surrounding tissues and structures; this was accomplished using the segmentation and image analysis program, Corview. Manual contouring of the endocardial borders of the LA was performed on each two-dimensional MRA slice. Further, the LAA was demarcated from the remainder of the LA using Corview's region-painting tool. This tool allows the user to select the LAA by painting the desired region on a three-dimensional ren-dering of the LA segmentation. Results. All twenty-eight scans underwent manual segmentation of the LA with further subseg-mentation of the LAA using the region-painting tool. The volume and shape of the LAA was easily identifiable once the segmentation of that structure was performed. Using these models, the volume, shape, and anatomical variability of the LAA, as well as the LA, was qualitatively assessed. Conclusions. The advent of MRA to visualize structural and pathophysiological changes in the LA and LAA has necessitated the development of efficient segmentation and image analysis tools. Specifically, the Corview software provides researchers with a means to delineate the LAA; individual analysis of the shape and volume of the LAA may reveal a clinical predictor for stroke occurrence in patients with AF. Fig. 1. MRA segmentation of the LA and LAA. (a) First, the MRA images of the LA and LAA anatomy are obtained. (b) Then the endocardial border of the LA (gray) is manual contoured with further subsegmentation of the LAA (white) using Corview's 3D region-painting tool. (c) An example 3D rendering of the LA and LAA, such as is used with the region-painting tool, showing the distinct anatomy of each structure. A Novel Image Processin g Method to Generate Three-Di mensiona l Models of the Left Atria l App endage for Stroke Occurrence Ana lysis Gregory Gardner, James Allen, Megan Montoya, Alan Morris, Josh Cates Comprehensive Arrhythmia and Research MAnagement (CARMA) Center University of Utah School of Medicine Scientific Computing and Imaging (SCI) Institute, University of Utah health sciences leap program James Allen Megan Montoya Joshua Cates |