1. Department of Radiology, Sejong General Hospital, Gyeonggi-do, Korea.
2. Department of Radiology, Seoul National University Hospital, 101 Daehangno, Jongno-gu, Seoul 110-744, Korea.
3. Institute of Radiation Medicine, Seoul National University College of Medicine, Seoul, Korea.
4. Department of Radiology, Soonchunhyang University Bucheon Hospital, Seoul, Korea.