X-rays are uncharged, and when they penetrate the body, they interact with substances in the body to produce “secondary particles” that ionize the substance, a phenomenon known as ionizing radiation, or radiation for short. Since radiation has the risk of causing cancer, it is also the most likely to cause alarm to patients and their families. 1.How much radiation is used in clinical examination? The reference value of radiation exposure: chest X-ray is about 1.1mSv (radiation measurement unit); the amount of radiation to be received for a general X-ray examination of the extremities is 0.01mSv, abdomen is 0.54mSv, pelvis is 0.66mSv, lumbar spine is 1.4mSv, and upper gastrointestinal tract is 2.55mSv. The size of CT radiation varies according to the location, chest CT is 8mSv; abdomen CT for 10mSv; pelvic CT for 10mSv. 2, the human body to the radiation safety dose The harmful effects of radiation is divided into deterministic effects and random effects, deterministic effects have a threshold, the severity depends on how much dose. For random effects there is no dose threshold, that is to say, a single exposure even if the dose of illumination is large, it is not necessarily a problem, with randomness. The human body has a certain tolerance to radiation exposure. According to the standards set by the International Commission on Radiological Protection, the human body can withstand up to 7Sv radiation. The total risk of radiation is 0.0165/Sv, which means that for every 1Sv (1Sv = 1000mSv) radiation dose received by the body, the chance of cancer will increase by 0.0165. 3.How much harm is there in taking a chest X-ray? It takes about 0.5 seconds to take a chest X-ray film when the exposure rate is about 0.045mSv/second in the examination area, so a patient who receives a chest X-ray examination is exposed to a radiation dose of about 0.023mSv, which will increase the chance of cancer by 0.0003795 times. 4.Cautions for X-ray examination: 1.When the X-ray machine is in working condition, the warning light on the door of the examination room will be on, and all the waiting persons should wait outside the protective door, and no unrelated persons should observe. 2.After the examination, you should leave the examination place in time. 3, pregnant women in the first trimester of pregnancy to do chest X-ray can wear a lead apron on the abdomen of pregnant women or choose a safer ultrasound or magnetic resonance. In summary, the dose of conventional diagnostic X-ray examinations (radiographs, chest X-ray, CT, CR, DR) is very small and limited to the safe dose, and the chance of causing cancer is even minimal, so there is no need to worry and refuse the examination.