1. From the Departments of Neurology (N.U.K., W.L.Y.), Radiology (A.J.M., D.A.S., R.T.H.), Anesthesia and Perioperative Care (W.L.Y.), Neurological Surgery (R.T.H., W.L.Y.), and Center for Cerebrovascular Research (A.S.A., M.C., D.A.S., W.L.Y.), University of California, San Francisco; and Philips Medical Systems (A.J.M.), Cleveland, Ohio.