1. Department of Pulmonary and Critical Care Medicine and Clinical Research Center for Chronic Obstructive Airway Diseases, Seoul, Korea.
2. Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
3. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Bundang CHA Hospital, CHA University College of Medicine, Seongnam, Korea.
4. Department of Radiology, East-West Neo Medical Center, Kyunghee University School of Medicine, Seoul, Korea.
5. Division of Pulmonology, Department of Internal Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Guri, Korea.
6. Department of Internal Medicine, College of Medicine, Kangwon National University, Chuncheon, Korea.
7. Department of Internal Medicine, Ewha Womans University Mokdong Hospital, Ewha Womans University College of Medicine, Seoul, Korea.
8. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
9. Division of Respiratory and Critical Care Medicine, Department of Internal Medicine, Korea University Anam Hospital, Korea University College of Medicine, Seoul, Korea.
10. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
11. Department of Internal Medicine, Kangnam Sacred Heart Hospital, Hallym University College of Medicine, Seoul, Korea.
12. Department of Internal Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
13. Department of Pulmonary and Critical Care Medicine, Ajou University School of Medicine, Suwon, Korea.
14. Department of Internal Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Korea.