1. J. Philip Kistler Stroke Research Center, Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston (N.S.R., S.M.G.).
2. Department of Neurology, Mayo Clinic, Jacksonville, FL (J.F.M.).
3. Department of Neurology, Johns Hopkins University, Baltimore, MD (R.G.).
4. Duke University, Durham, NC (L.W.).
5. Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston (K.H.).