Peak Geodesic Concentration: A measure of WM complexity in HARDI

We design and evaluate a scalar measure for HARDI data called Geodesic Concentration (GC) that characterizes the integrity of white matter (WM), by quantifying the anisotropic concentration of water diffusion. Mathematically, GC is defined as the concentration relative to the peak, identified in the HARDI model fitted to the data. As GC reflects the degree of directionally coherent diffusion, it is sensitive to the presence of single or multiple fiber populations within a voxel and hence is able to characterize complexity of WM, yielding a unique HARDI based scalar measure that can be used for evaluation of pathology. GC properties are elucidated with the help of simulated data and its applicability to population studies is evaluated on a population of autism patients and controls.