1. From the Department of Radiology and Research Institute of Radiology (Y.A., S.M.L., J.C., K.H.D., J.B.S.), Department of Cardiothoracic Surgery (S.C.), and Department of Clinical Epidemiology and Biostatistics (M.J.K.), University of Ulsan College of Medicine, Asan Medical Center, 88 Olympic-ro 43-gil, Songpa-gu, Seoul 138-736, Republic of Korea.