Voxel similarity measures for 3-D serial MR brain image registration

We have evaluated eight different similarity measures used for rigid body r egistration of serial magnetic resonance (MR) brain scans. To assess their accuracy we used 33 clinical three-dimensional (3-D serial MR images, with deformable extradural tissue excluded by manual segmentation and simulated 3-D MR images with added intensity distortion. For each measure we determin ed the consistency of registration transformations for both sets of segment ed and unsegmented data. We have shown that of the eight measures tested, t he ones based on joint entropy produced the best consistency. In particular , these measures seemed to be least sensitive to the presence of extradural tissue. For these data the difference in accuracy of these joint entropy m easures, with or without brain segmentation, was within the threshold of vi sually detectable change in the difference images.