1. From the Stroke and Neurovascular Regulation Laboratory (H.K.S., M.N., M.A.M., C.A.) and the Martinos Center for Biomedical Imaging (P.B.J., H.A., D.A.B.), Department of Radiology, and the Stroke Service and Neuroscience Intensive Care Unit, Department of Neurology (C.A.), Massachusetts General Hospital, Harvard Medical School, Charlestown, Mass.