1. From the National Institute of Neurological Disorders and Stroke (H.C.), NIH, Bethesda, MD; Warren Alpert Medical School of Brown University (M.K.), Providence, RI; Department of Radiology (M.C.), University of Maryland Medical Center, Baltimore; Department of Radiology (A.M.), Yale New Haven Hospital, CT; and Departments of Radiology, Neurology, and Neurosurgery (D.G.), University of Maryland Medical Center, Baltimore.