1. From the Department of Radiology (J.G.F., D.L.L., A.M.G.S., R.M.L., D.B.W., R.S.K., V.S., L.Y., S.L., A.I., C.H.M.), Department of Physiology and Biomedical Engineering (D.R.H.), and Department of Health Science Research (M.P.J.), Mayo Clinic, 200 First St SW, Rochester, MN 55905; and Department of Health Science Research, Mayo Clinic, Jacksonville, Fla (R.E.C.).