1. From the Carl E. Ravin Advanced Imaging Laboratories, Department of Radiology, Duke University Medical Center, 2424 Erwin Rd, Suite 302, Durham, NC 27705 (P.S., E.A., W.P.S., D.M., R.C.N., E.S.); and Department of Physics, North Carolina State University, Raleigh, NC (P.S.).