The so-called 16 layers, 8 layers and 64 layers are only indicators of CT machine equipment and scanning speed, and have no relationship with the amount and size of radiation. CT is a technical device that uses X-rays for imaging and has radiation, but the current medical CT, including flat films, actually has a very low radiation dose. The radiation dose of CT head is equivalent to the radiation given by nature during 10 days outside, which will not cause any damage to the body. Therefore, it is not necessary to take the radiation of CT examination as too much consideration, but should do a certain examination according to the needs of the condition without delay. When you arrive at the hospital, you must cooperate with the doctor’s requirements, for example, chest CT requires inhalation and closure, if the examination is not successful to be rescanned once, it is equivalent to unintentionally increase the chance of radiation, the amount of radiation received will increase.