1. A computer-implemented method of registration of brain images comprising: registering, through a processor, at least two full volumes of brain images based on a projection based reference image, wherein the registration is performed based on a sharing of mass in a predetermined direction; and registering, through the processor, at least two partial volumes in regions of interest through modified mutual information, wherein the modified mutual information comprises mutual information modified to include a parameter related to an extent of overlap between the regions of interest and a weight assigned to the extent of overlap.