1. From the Department of Radiology (A.J., M.L.S., M.S., S.J.B., J.A.C.L., D.A.B.), Division of Cardiology (H.C., J.A.C.L., D.A.B., H.T.), Johns Hopkins University School of Medicine, Baltimore, Md; and Radiology and Imaging Sciences (D.A.B.), National Institutes of Health, Baltimore, Md.