1. From the Department of Radiology, Johns Hopkins Hospital, 601 N Caroline St, Baltimore, MD 21231 (M.D.A.); Department of Radiology & Biomedical Imaging, University of California, San Francisco, San Francisco, Calif (E.G.); Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Mass (F.D., S.I.L.); and Department of Radiology, University of Pittsburgh, Pittsburgh, Pa (S.W.).