1. Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Korea.
2. Department of Radiology, Konkuk University Hospital, Konkuk University School of Medicine, Seoul 143-914, Korea.
3. Department of Radiology, Kangwon National University Hospital, Kangwon National University College of Medicine, Chunchon 200-701, Kangwondo, Korea.