Non-rigid registration of high angular resolution diffusion images represented by Gaussian mixture fields. 
In this paper, we present a novel algorithm for non-rigidly registering two high angular resolution diffusion weighted MRIs (HARDI), each represented by a Gaussian mixture field (GMF).  We model the non-rigid warp by a thin-plate spline and formulate the registration problem as the minimization of the L2 distance between the two given GMFs.  The key mathematical contributions of this work are, (i) a closed form expression for the derivatives of this objective function with respect to the parameters of the registration and (ii) a novel and simpler re-orientation scheme based on an extension to the "Preservation of Principle Directions" technique.  We present results of our algorithm's performance on several synthetic and real HARDI data sets.