1. Department of Pulmonary and Critical Care Medicine and Clinical Research Center for Chronic Obstructive Airway Diseases, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
2. Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
3. Department of Internal Medicine, Kangwon National University College of Medicine, Chuncheon, Korea.