Registration of head CT images to physical space using multiple geometrical features

We recently reported a hybrid registration technique that uses a weighted combination of multiple geometrical feature shapes (IEEE Trans. Med. Imaging 15: 836-849, 1996). In this study we use the weighted geometrical feature (WGF) algorithm to register CT images of the head to physical space using the skin surface only, the bone surface only, and various weighted combinations of these surfaces and one fiducial point (centroid of a bone-implanted marker). We use data acquired from six patients that underwent temporal lobe craniotomies for the resection of cerebral lesions. Each patient had four external markers attached to transcutaneous posts screwed into the outer table of the skull. We evaluate and compare the accuracy of the registrations obtained using these various approaches by using as a gold standard the registration obtained using three of the four bone-implanted markers (the remaining marker is used in the various combinations). The results demonstrate that a combination of geometrical features can improve the accuracy of CT-to-physical space registration. The WGF algorithm might thus be useful in various image-guided surgical systems.