1. Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea.
2. Department of Radiology, Chungnam National University Hospital, Chungnam National University School of Medicine, Daejeon 301-721, Korea.
3. Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea.