Comparison of local external force functions for non-rigid registration of 3D medical images

Non-rigid volumetric registration has many applications, including inter-patient image fusion, motion quantification, and automatic atlas-based segmentation. Computation time is often a limiting factor in using current methods in clinical environments. Minimizing computation time requires both the internal and the external force updates to be as efficient as possible. In this article, we concentrate on the choice of the external force function. We compare different methods based on optical flow and propose a new correlation-based external force function. In addition, we propose an acceleration technique and study its effect on image quality and the speed of convergence. The results indicate that the acceleration technique improves both the speed and quality, and increases the stability of all the external force methods considered.