1. From the Departments of Radiology (D.R.J., J.M.M., L.J.E., T.J.K., J.B.G.), Neurology (D.R.J.), and Laboratory Medicine and Pathology (C.G., R.A.V.), Mayo Clinic, 200 First St SW, Rochester, MN 55905; and Department of Biomedical and Neuromotor Sciences, University of Bologna, Bologna, Italy (C.G.).