1. Department of Radiology and the Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul 138-736, Korea.
2. Department of Radiology, University of California at San Francisco, San Francisco Veterans Administration Medical Center, 4150 Clement St., San Francisco, CA 94121.
3. Department of Radiology and the Institute of Radiation Medicine, Seoul National University Hospital, Seoul 110-744, Korea.
4. Department of Radiology, Seoul National University Bundang Hospital, Seongnamsi 468-802, Korea.