1. Department of Radiology, Seoul National University College of Medicine, Seoul 110-744, Korea.
2. Department of Radiology, Seoul National University Hospital, Seoul 110-744, Korea.
3. Department of Radiology, Research Institute and Hospital, National Cancer Center, Gyeonggi-do 410-769, Korea.
4. Department of Radiology, Seoul National University Bundang Hospital, Gyeonggi-do 463-707, Korea.
5. Department of Radiology, Seoul National University Boramae Hospital, Seoul 156-707, Korea.
6. Department of Radiology, Kangwon National University College of Medicine, Gangwon-do 200-722, Korea.