1. From the Departments of Radiology (H.A., C.E., Y.C., W.L.), Biostatistics (H.Z., Y.L.), and Neurology (W.J.P.), University of North Carolina at Chapel Hill, Chapel Hill, NC; and the Departments of Neurology (A.L.F., R.P., J.-M.L.) and Radiology (K.V.), Washington University, School of Medicine, St Louis, Mo.