CT is a visual image formed after scanning a human part of the body with X-ray beam, gamma ray, ultrasound, etc. The CT value is a response to the density of the human body. The CT value is a response to the density of the human body, it is not a constant amount, generally different parts of the human body CT value is also different, CT value is the CT image of each tissue and X-ray attenuation coefficient equivalent value, is based on the body of different tissues, organs after the absorption of X-ray attenuation coefficient conversion, it reflects the ability to block X-rays. In general, the CT value of human tissues is between -1000 and +1000, among which air is -1000, water is 0, and bone cortex is +1000, and by analogy, the higher the density of the part, the higher the CT value. The CT value is an objective indicator that is automatically measured by a standardized machine and is generally considered reliable. However, CT diagnostic radiation dose is relatively high and is not recommended for pregnant women to avoid increasing the chance of fetal malformation.