1. From the Department of Radiology and Biomedical Imaging, University of California, San Francisco, 505 Parnassus Ave, San Francisco, CA 94143-0628 (M.C.C., B.M.Y., A.S.P., S.C.B.); and Department of Radiology, Wake Forest University Baptist Medical Center, Winston-Salem, N.C. (J.J.O.).