Multimodal nonrigid registration using a stochastic gradient approximation

We present a new fast implementation of a nonrigid registration algorithm, based on a finite element elastic deformation model using the mutual information metric with a linear elastic regularization constraint. The algorithm was parallelized for symmetric multiprocessor architectures. A simultaneous perturbation stochastic approximation (SPSA) optimization scheme was used to maximize the objective function. This algorithm was applied to capture nonrigid deformations of pre-procedural to post-procedural images of tumor radio-frequency (RF) ablation in the liver and nonrigid deformations of intraoperative to preoperative prostate images.