1. From the Department of Radiology and Molecular Imaging Program at Stanford (H.N., S.M.T., K.L., S.Z., H.E.D.) and Division of Cardiovascular Medicine (P.Y., M.M.), Stanford School of Medicine, 725 Welch Rd, Room 1665, Stanford, CA 94305-5654; and Department of Materials Science and Engineering, Stanford University, Stanford, Calif (S.J.M.).