1. Department of Radiology, Cheju Halla Hospital, Jeju-do 690-766, Korea.
2. Department of Radiology, Uijongbu St. Mary's Hospital, The Catholic University of Korea, Kyunggi-do 480-717, Korea.
3. Department of Radiology, Kangnam St. Mary's Hospital, The Catholic University of Korea, Seoul 137-701, Korea.