1. From the Department of Biomedical Engineering, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, 110 8th St, Biotech 4231, Troy, NY 12180 (J.Z., H.C., G.W., P.Y.); and Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Mass (G.D., M.K.K.).