1. From Departments of Radiology (G.V.G., L.R., E.F.H., G.J.H., R.G.G., M.H.L.) and Neurology (E.C.S.C., K.L.F., A.B.S., M.J.C., W.J.K.), Massachusetts General Hospital; Boston, Mass; Departments of Neurology (T.B., W.S.S.), and Radiology (W.P.D.), University of California at San Francisco, San Francisco, Calif.