1. Department of Radiology, Seoul National University Bundang Hospital, Seongnam 463-707, Korea.
2. Department of Radiology, Chung-Ang University Hospital, Seoul 156-755, Korea.
3. Department of Radiology, Samsung Medical Center, Seoul 135-710, Korea.
4. Department of Radiology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul 110-744, Korea.
5. Department of Radiology, Gyeongsang National University Hospital, Jinju 660-702, Korea.