1. From Department of Radiology (M.W.), Neuroradiology Division, University of Virginia, Charlottesville, Va; Department of Radiology (D.D.A., N.B., A.D.F., K.O., K.C., J.D.C., S.S.), Department of Epidemiology and Biostatistics (S.-C.C.), University of California, San Francisco, Department of Radiology, San Francisco, Calif.