Matthew T Whitehead1,2, Bonmyong Lee3, Andrea Gropman4,5. 1. Department of Radiology, Children's National Medical Center, 111 Michigan Ave. NW, Washington, DC, 20010, USA. MWhitehe@childrensnational.org. 2. The George Washington University School of Medicine, Washington, DC, USA. MWhitehe@childrensnational.org. 3. Department of Radiology, The Johns Hopkins Medical Institute, Baltimore, MD, USA. 4. The George Washington University School of Medicine, Washington, DC, USA. 5. Department of Neurology, Children's National Medical Center, Washington, DC, USA.