1. Pulmonary Unit, Department of Internal Medicine, Dongsan Hospital, Keimyung University School of Medicine, Daegu, Korea,
2. Department of Preventive Medicine, Keimyung University School of Medicine, Daegu, Korea
3. Department of Internal Medicine, College of Medicine, Pochon CHA University, Kyungkido, Korea
4. Department of Diagnostic Radiology, Dongsan Hospital, Keimyung University School of Medicine, Daegu, Korea
5. Pulmonary/Critical Care Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA