1. Department of Clinical Epidemiology and Biostatistics, Asan Medical Center, Seoul 138-736, Korea.
2. Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea.
3. Department of Radiology, NYU Langone Medical Center, New York, NY 10016, USA.
4. Office of Clinical Research Information, Asan Medical Center, Seoul 138-736, Korea.
5. Department of Preventive Medicine, University of Ulsan College of Medicine, Seoul 138-736, Korea.