1. From the Departments of Neurosurgery (B.G., J.B., D.V., C. Ahn, M.E., M.A., D.B., L.M.), Radiological Sciences (J.P.V., N.S., A.B.), and Electrical Engineering (S.M.), University of California, Los Angeles, 300 Stein Plaza, Suite 554E, Los Angeles, CA 90095; and Department of Neurosurgery, University of California, San Francisco, San Francisco, Calif (C. Ames).