1. Department of Radiology, Ansan Hospital, Korea University College of Medicine, Ansan 425-707, Korea.
2. Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea.
3. Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea.
4. Department of Radiology, Research Institute of Radiological Science, Yonsei University College of Medicine, Seoul 120-752, Korea.
5. Department of Radiology, Seoul National University College of Medicine, Seoul 110-744, Korea.
6. Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea.