1. From the Department of Radiology, Cardiothoracic Division (M.F.B., A.C., S.A., F.U.K.), Department of Radiology (Y.X.), and Department of Emergency Medicine (D.B.D.), UT Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd, Dallas, TX 75390; and Department of Radiology, University of Pennsylvania, Philadelphia, Pa (H.L.).