1. National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda (H.C.).
2. Department of Neurology, MedStar Georgetown University Hospital, Washington DC (H.C.).
3. Division of Interventional Neuroradiology, Department of Radiology (H.C., M.C., G.J., D.G.), University of Maryland Medical Center, Baltimore.
4. Warren Alpert Medical School, Brown University, Providence, RI (M.K.).
5. Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT (M.K., A.M.).
6. Department of Neurology (S.C.), University of Maryland Medical Center, Baltimore.