1. From the Department of Radiology, Cardiothoracic Division, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Room E6.122H, Dallas, TX 75390-9316 (F.U.K., O.K.O., S.A., P.R.); the Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, Pa (E.J.M.B.); and the Department of Radiology, University of Michigan Health System, Ann Arbor, Mich (P.P.A.).