1. From the Department of Radiology, Cardiovascular Division (S.G., N.M.S., B.B.G., S.S.H.), and Department of Medicine, Cardiology Division (M.J.W.), Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114; Department of Radiology (M.L.S.) and Department of Medicine, Cardiovascular Division (R.B.), Brigham and Women’s Hospital, Boston, Mass.