1. From the Department of Radiology (D.G.M., J.K., B.D., J.G.M.), Center for In Vivo Microscopy (D.G.M., B.D.), Department of Biomedical Engineering (E.A.B., Z.W., B.D.), Department of Medicine (L.M., C.B., H.P.M., R.T.), and Department of Medical Physics (B.D.), Duke University, DUMC Box 3302, Durham, NC 27710.