1. Department of Radiology, Seoul National University Bundang Hospital, Gyeongi-do 463-707, Korea.
2. Department of Radiology, Seoul National University College of Medicine, Seoul 110-744, Korea.
3. Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Gyeongi-do 463-707, Korea.
4. Department of Neurosurgery, Seoul National University Bundang Hospital, Gyeongi-do 463-707, Korea.