1. From the Department of Anesthesia (J.S.H., J.A.F.), University of Toronto and University Health Network, Toronto, Canada; the Department of Physiology (J.S.H., J.A.F., M.T.), University of Toronto, Toronto, Canada; the Division of Neurosurgery (A.A., M.T.), Department of Surgery (M.T.), University Health Network, Toronto, Canada; and the Division of Neuroradiology (D.M.M., J.P., A.P.C., D.J.M.), Department of Medical Imaging, University Health Network and the University of Toronto, Toronto, Canada.