1. From the Department of Radiology, Massachusetts General Hospital, 55 Fruit St, White 270, Boston, MA 02114 (A.P., A.A.N., M.P., F.M., A.K., D.V.S.); Department of Radiology, Hospital Universitario Jose Eleuterio Gonzalez, Monterrey, Mexico (A.A.N.); and Department of Radiology, University of Washington, Seattle, Wash (D.V.S.).