1 From the Department of Radiology and Department of Neurosurgery, University of Pennsylvania, 3400 Spruce St, Philadelphia, PA 19104 (S.M.); Department of Radiology, Wake Forest University School of Medicine, Winston-Salem, NC (P.M.B.); and Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, Calif (C.M.G.).