Registration of multiple MRI scans by matching bony surfaces

An algorithm originally developed for retrospective registration of brain image studies (CT, MRI, PET, SPECT) has been modified for use in registering multiple image data sets in other areas of the body where rigid bony structures can be identified in both scans of interest. The original algorithm relied upon matching 3D models of a single surface, segmented from each scan to be registered. This method has been extended to match any number of pairs of surface models. The ray-tracing algorithm used has also been modified to allow the use of surfaces which are far from spherical in shape, such as long bones in the extremities and the bony pelvis, for which the original algorithm was not well suited. Application to registration of multiple MRI scans of a thigh containing a large soft tissue sarcoma is described.