CT examination is an imaging technique, specifically an electronic computerized X-ray tomography. It is based on the different absorption and transmission rates of X-rays by different tissues of the human body, and applies a highly sensitive instrument to measure the human body, and then inputs the data obtained from the measurement into an electronic computer. CT can better display organs made up of soft tissue, such as the brain, spinal cord, mediastinum, lungs, liver, gallbladder, pancreas, and pelvic organs, etc. CT images are expressed in different shades of gray, reflecting the degree of absorption of X-rays by organs and tissues. Thus, as with the black and white images shown on X-ray images, black shadows indicate areas of low absorption, i.e., low density, such as the lungs, which contain a lot of gas, and white shadows indicate areas of high absorption, i.e., high density, such as the bones.