1 From the Department of Medicine, Baylor College of Medicine, Houston (S.V.S.); and the Departments of Medicine (L.X.M.), Radiology (S.P.R.), and Neurology (E.M.R.), Harvard Medical School, the Departments of Medicine (L.X.M.) and Neurology (E.M.R.), Beth Israel Deaconess Medical Center, and the Department of Radiology, Massachusetts General Hospital (S.P.R.) - all in Boston.