CT and radiographs are two different tests, but they are both scanned and imaged by X-rays. A radiograph produces a single image, while a CT shows multiple images. The CT scan layer thickness can reach 0.5 mm, and the CT scan image can be reconstructed in three dimensions to observe the lesion from coronal, sagittal and cross-sectional angles, and to clarify the relationship between the lesion and the surrounding tissues and blood vessels. CT can be used for screening of early lung cancer.