1. From the Division of Cardiovascular Imaging (V.B., J.E.S., S.H., B.B.G.) and Department of Radiology (V.B., J.E.S., H.K., S.H., B.B.G.), Massachusetts General Hospital, 55 Fruit St, White 270, Boston, MA 02114; and Institute for Diagnostic and Interventional Radiology, University Hospital Frankfurt, Frankfurt, Germany (J.E.S.).