1. From the Mallinckrodt Institute of Radiology (H.A., C.E., K.D.V., J.-M.L.) and Department of Neurology (A.L.F., Y.C., J.-M.L.), Washington University, School of Medicine; and Department of Biostatistics (H.Z.), Department of Neurology (W.J.P., W.L.), and Department of Radiology (W.L.), University of North Carolina at Chapel Hill.