1. Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
2. Acute Cerebrovascular Diagnostics Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland.
3. Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland.
4. Acute Studies Core, Center for Neuroscience and Regenerative Medicine, Bethesda, Maryland.