1. From the Mallinckrodt Institute of Radiology, Washington University, St. Louis, Mo (S.B.); Department of Cardiovascular Medicine, Mayo Clinic, Rochester, Minn (N.K., N.Y.T.); Banner University Medical Center, Phoenix, Ariz (M.F.M.); and Department of Radiology, Cardiovascular Imaging, Mayo Clinic, 200 1st Street SW, Rochester, MN 559905 (P.S.R.).