CT and chest radiographs are two common tests used in radiology. Both examinations utilize X-rays, but CT is a tomography, which has a higher density resolution and no overlapping images of tissues and organs. Chest radiographs, on the other hand, have overlapping images, so they have a lower density resolution, and lesions are easily obscured and are not as clear as those shown by CT. However, CT examination has a higher radiation dose to the body because of the number of layers scanned. Chest X-ray is an instantaneous shot, the radiation dose is very low, about the same as many natural background radiation, can be ignored. Moreover, the cost of CT instrument is high, so the examination cost will be relatively high. The operation of CT is relatively complex, chest film is relatively simple, so the chest film is usually used as a means of routine physical examination, and only when there is a problem will the patient be asked to do further CT examination.