1. From the Department of Radiology, University of Wisconsin School of Medicine and Public Health, E3/311 Clinical Science Center, 600 Highland Ave, Madison, WI 53792-3252 (S.J., P.M.G., T.J.Z., S.J.L., P.J.P.); and Department of Diagnostic Radiology, National Institutes of Health Clinical Center, Bethesda, Md (R.M.S.).