Polar appearance models: A fully automatic approach for femoral model initialization in MRI

Various segmentation approaches in medical image processing, such as Level Sets, Active Shape Models, and Active Appearance Models require initial localization of the structure of interest (SOI). In this work we present a novel fully automatic model initialization approach in MRI, that is applicable for structures that are mostly convex in the axial plane. We propose a training model, namely the Polar Appearance Model, that encapsulates both the transition from the structure of interest to its vicinity in polar space and the intensity distribution within the structure in euclidean space. We present our approach on the example of femoral model initialization in MRI and compare our results to a standard voxel-based registration approach that allows similarity transformations.