1. From the Departments of Radiology (G.A.C., E.N., A.M.T., F.T.L.), Cardiology (P.J.M.), and Biomedical Engineering (C.L.B.), University of Wisconsin–Madison School of Medicine and Public Health, 600 Highland Ave, Madison, WI 53792; and Research Animal Resources Center (D.J.S.) and Department of Biostatistics (S.H.), University of Wisconsin–Madison, Madison, Wis.