The precise and accurate size of DLT is a prerequisite to ensure its accurate position of its placement. Three-dimensional (3D) reconstruction technology can accurately reproduce the tracheobronchial structure to improve the correct size selection of DLT. To make it simpler, the investigators developed an automatic comparison software for 3D reconstruction based on computed tomography data (3DRACS). In this study, the investigators aimed to prove that 3DRACS is much more efficient in endobronchial intubation compared to the traditional method.