1. From the Departments of Radiological Sciences (S.M., A.R.P., Y.Z., I.A.) and Statistics (Z.Y.), University of California Irvine, Medical Sciences I, B-140, Irvine, CA 92697; Department of Radiological Sciences, University of California San Diego, San Diego, Calif (J.R.); and Department of Radiology, University of Pennsylvania, Philadelphia, Pa (M.I.).