1. Center for Neurologic Diseases (Drs. Khoury, Hohol, Mackin, and Weiner) and the Radiology Department (Drs. Guttmann, Ahn, Hsu, Kikinis, and Jolesz), Brigham and Women's Hospital, Boston, MA; and the Biostatistic Department (Dr. Orav), Harvard School of Public Health, Boston, MA.