1. Department of Radiological Sciences, University of California, Irvine, 101 The City Dr S, Rte 140, Orange, CA 92868.
2. Department of Radiology, Oklahoma State University Medical Center, Tulsa, OK.
3. Department of Radiology, St. Luke's International Hospital, Tokyo, Japan.
4. Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan.