1Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Research Institute of Radiology, 388–1, Pungnap-dong, Songpa-ku, Seoul, 138–736, Korea.2Department of Radiology, Bundang CHA Hospital, University of Pocheon Jungmoon College of Medicine, 183–8 Yatap-dong, Bundang-Ku, Seongnam-City, Gyeonggi-Do, 463–712, Korea.3Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Asan Medical Center, University of Ulsan College of Medicine, Research Institute of Radiology, 388–1, Pungnap-dong, Songpa-ku, Seoul, 138–736, Korea.4Department of Internal Medicine, Bundang CHA Hospital, University of Pocheon Jungmoon College of Medicine, 183–8 Yatap-dong, Bundang-Ku, Seongnam-City, Gyeonggi-Do, 463–712, Korea.5Department of Internal Medicine, Ewha Womans University Mokdong Hospital, College of Medicine, Ewha Womans University, Seoul, Korea.6Seoul, Korea.