1. Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea.
2. Department of Respiratory and Critical Care Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea.
3. Department of Emergency Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea.