1. From the Department of Radiology & Biomedical Imaging, University of California, San Francisco, 505 Parnassus Ave, L-352, San Francisco, CA 94143 (J.D.R., T.G., M.J.B., D.M.W., J.E.V.M.); Subtle Medical, Menlo Park, Calif (A.S., T.Z., L.W., E.G.); and Department of Radiology, Stanford University, Stanford, Calif (G.Z.).