CT examinations are certainly a little harmful to the body, but negligible. The current CT examination of the chest or CT scan of the chest, the received dose of radiation is about 1 mSv, but 20 years ago, the ordinary CT to do a chest scan, 100-150 mSv, that is, the radiation dose received now is only 20 years ago less than 1%. Rays harmful to health, there are two situations: 1, cumulative effect: cumulative effect is the more exposure to the rays, the greater the possible harm to the body; 2, random effect: random effect, as the name suggests, is the harm to the body is very contingent. The time to do CT must go to do, do not be affected by the so-called radiation. Some people think that doing CT four times a year will be harmful to the body, this statement is not based on science.