Physics-Based Shape Deformations for Medical Image Analysis Ghassan Hamarneh1,2 and Tim McInerney3,2 1 Dept. of Signals and Systems,Chalmers University of Technology,Göteborg 41296, Sweden 2 Dept. of Computer Science,University of Toronto,Toronto M5S 3H5, Canada 3 School of Computer Science,Ryerson University, Toronto M5B 2K3, Canada Abstract Powerful, flexible shape models of anatomical structures are required for robust, automatic analysis of medical images. In this paper we investigate a physics-based shape representation and deformation method in an effort to meet these requirements. Using a medial-based spring-mass mesh model, shape deformations are produced via the application of external forces or internal spring actuation. The range of deformations includes bulging, stretching, bending, and tapering at different locations, scales, and amplitudes. Springs are actuated either by applying deformation operators or by activating statistical modes of variation obtained via a hierarchical regional principal component analysis. We demonstrate results on both synthetic data and on a spring-mass model of the corpus callosum, obtained from 2D mid-sagittal brain MRI slices.