1. From the Department of Radiology and Biomedical Imaging, University of California, San Francisco, 505 Parnassus Avenue, San Francisco, CA (M.C.C., Y.L., D.J.S., O.A.G., C.M.G., J.L.C.) and the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD (B.P.S.).