1. Department of Radiology, Graduate School of Medicine, Kyung Hee University, Seoul 130-872, Korea.
2. Department of Radiology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul 110-744, Korea.
3. Department of Radiology, Chung-Ang University Hospital, Seoul 156-755, Korea.
4. Department of Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul 110-744, Korea.