1. Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea.
2. Department of Radiology, Seoul National University Bundang Hospital, Seongnam 463-707, Korea.
3. Department of Radiology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul 110-744, Korea.
4. Department of Preventive Medicine, Dong-A University School of Medicine, Busan 602-715, Korea.