1. Department of Radiology and Research Institute of Radiological Science, Severance Children's Hospital, Yonsei University College of Medicine, Seoul 120-752, Korea.
2. Department of Pediatric Urology, Severance Children's Hospital, Yonsei University College of Medicine, Seoul 120-752, Korea.
3. Department of Pediatrics, Severance Children's Hospital, Yonsei University College of Medicine, Seoul 120-752, Korea.