1. Department of Radiology, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea.
2. Korea Institute for Accreditation of Medical Image, Korea.
3. Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea.
4. Department of Radiology, Seoul National University College of Medicine, Seoul 110-744, Korea.
5. Department of Radiology, Yonsei University College of Medicine, Seoul 120-752, Korea.