1. Department of Radiology, Seoul National University Hospital, Seoul 03080, Korea.
2. Department of Radiology, Seoul National University College of Medicine, Seoul 03087, Korea.
3. Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul 03087, Korea.
4. Department of Radiology, Konkuk University Medical Center, Seoul 05030, Korea.
5. Philips Healthcare Korea, Seoul 04342, Korea.