The most common concern about radiation exposure during imaging examinations is that patients are exposed to radiation when they visit hospitals for diagnosis and treatment of illnesses that involve medical imaging.X-rays (e.g., chest X-rays, barium meal gastrointestinal imaging, etc.), CT examinations, digital subtraction angiography (DSA), and nuclide scans, PET-CT, are all subjected to radiation exposure. Radiation exposure. Ultrasound and MRI are radiation-free. Yang Jingzhen, Medical Imaging Center of China Petroleum Central Hospital I. X-ray examination, CT and DSA radiation belongs to the external exposure to X-ray examination, fluoroscopy exposure to more rays, therefore, in addition to the special needs of the provisions of the patient is not permitted to do fluoroscopy. x-ray photographs of patients to receive the dose of radiation: a chest radiographs: 0.2 ~ 1.2mSv; lumbar vertebrae in front of the side film: about 1.4mSv; abdominal orthopedic: about 0.54mSv; pelvic orthopedic: about 0.54mSv; the radiation dose received by patients. mSv; pelvic position: about 0.66 mSv; gastrointestinal X-ray barium meal or barium enema depending on the examination time, the number of films taken and the radiation dose received varies. x-ray photo examination, for the reproductive organs (especially children’s testicles or ovaries) thyroid, eye lens and other sensitive organs of the radiation damage to the lead products should be used to cover the protection. Pregnant women should be prohibited from undergoing X-ray examinations, especially within 3 months. The general population should not undergo frequent X-ray examinations for a short period of time, and DSA is an imaging technique that uses X-rays for angiography, such as coronary arteriography and stenting of blood vessels under the guidance of X-rays. Coronary angiography patients receive a dose of 2.7-8.8 mSv (depending on the skill level of the operator) CT examinations can expose patients to a certain dose of X-ray radiation. In particular, the application of multi-phase spiral CT scanning technology (i.e., to do the arterial phase, venous phase, delayed phase in CT enhancement scanning), CT wide range of angiography, etc., the patient’s radiation exposure is relatively large, and there will be damage to ray-sensitive organs (there are a lot of studies on the relationship between radiation and the induction of cancer, but the occurrence of cancer is a complex multifactorial, and autoimmunity is one of the important factors). Foreign studies have reported that the dose due to routine diagnostic CT: 8 mSv for the chest; 10 mSv for the abdomen; and 14 mSv for coronary imaging of the heart.Some people in China have reported that: one time low-dose CT of the chest: 0.5~1.0 mSv; one time routine-dose CT of the chest: 3~5 mSv; and one time coronary CT imaging: 15 mSv; and the 64-row and 320-row helical CTs have been reduced to 7.5 mSv, 6.0 mSv; a full abdominal scan with enhancement (i.e., from the diaphragm to the pubic symphysis, e.g., small bowel imaging, full abdominal scanning, extensive abdominal angiography, etc.): low-dose scanning of 13-16 mSv, conventional-dose scanning: about 36 mSv; if multiple dynamic enhancement scans are performed, then the dose received by the patient will be increased accordingly. (Note: “low dose”: is the use of 30 ~ 50mA smaller X-ray tube current, so that the patient receives a lower dose of radiation in the examination) CT in addition to the examination of disease must be, generally not for children in the gonadal region of the scan. 3 months pregnant women are generally not for abdominal scanning. Women of childbearing age should avoid CT examinations. Do not undergo frequent examinations within a short period of time. The indications for CT examinations involving high doses of radiation should be strictly controlled. It is recommended to choose non-radiation methods such as ultrasound, MRI examination. Second, the nuclide imaging examination is an internal irradiation that through intravenous injection into the body to introduce radioactive drugs (called nuclides), so the internal irradiation can be formed rays, for the general public is within the safety range, but for special groups should be implemented special measures: 1, children have a strict dose of medication, to have a pediatrician to assist in the examination. 2, pregnant women if the implementation of the nuclide imaging examination must have a justified reason, in particular, it is necessary to Control the examination of radiopharmaceuticals that can be transmitted through the placenta and enter fetal tissues. 3. Women of childbearing age should consider whether they are pregnant when applying for a nuclide examination and should strictly control the indications, and if menstruation has already expired or ceased on the day of the examination, the examination should be regarded as a pregnancy. In general, pregnancy should not be allowed to occur until six months after the examination. 4. Nuclide examination for breastfeeding women should weigh the risk of irradiation of human milk-fed babies against the benefits of timely cure of the mother’s disease by diagnosis and treatment. The use of nuclides for internal examination is generally postponed unless it is absolutely necessary. If the test is performed, breastfeeding is stopped for a certain period of time after the test. Third, PET-CT (PET-CT) belongs to the fusion machine technology that has both internal and external irradiation (combining the two imaging devices into one.) The radiation dose of PET/CT comes from both radionuclide and CT, that is to say, to do this kind of examination, the patient has to receive two kinds of radiation from the radionuclide and the X-ray. “Is a PET/CT exam safe or not? How long is the interval between two examinations better?” PET/CT was first used in China in 2002, and with the continuous upgrading of PET/CT equipment, the dose of nuclides used in this part of PET is getting smaller and smaller; the scanning speed used in this part of CT is getting faster and faster, and the radiation dose control is getting better and better. Let’s take a look at the patient’s radiation in the PET CT examination: 1, nuclide radiation: PET uses the vast majority of radioactive radiation from fluorine-18 (18F), 18F emits positrons, generating high-energy γ (gamma) rays, the human body has a certain amount of radiation, the patient receives a PET/CT examination, in which PET scanning the required nuclides to produce a radiation dose of about 4.6 ~ 6.2 mSv, with the upgrading of equipment, the third generation of PET/CT products, the radiation dose to the examinee is reduced to about 3.8 mSv. The radiopharmaceuticals used are non-sensitizing and do not pose a hazard to the human body. The radionuclide used is an ultra-short half-life isotope that decays very quickly, and about 50% of the dose is excreted in the urine 2 hours after injection of the radiopharmaceutical, and completely disappears from the body within a few hours. By drinking more water and accelerating the excretion of drugs, the radiation dose of nuclides can also be appropriately reduced. 2. The radiation dose received by the patient during the examination mainly comes from the X-rays used for CT scanning, but the CT used for PET/CT is lower than the dose of conventional CT. The new PET-CT is equipped with a CT model that makes a whole body examination X-ray radiation dose from the original 15mSv or so reduced to about 7.5mSv (7.0-10.2). However, the CT dose can be as high as 14.1~18.6mSv if the high mA scanning mode or enhanced scanning mode is used, so the increased dose in PET/CT scanning mainly depends on the CT scanning mode. CT scanning in routine PET/CT imaging is generally recommended to use low-dose (low mA) scanning mode, and suspicious organs are localized to diagnostic dose scanning to minimize the radiation dose to the recipient. Although PET / CT examination has a certain radiation (the patient receives γ, X-ray two kinds of radiation total dose of about 11 ~ 18mSv or so), for patients with indications to receive PET / CT examination of the benefit is significantly greater than the risk of radiation, and even get the opportunity to save lives. However, it should not be abused without limitations. Lin Hongwei, a surgical oncologist at PLA 306 Hospital, was the first to openly criticize PET-CT on Weibo for being “abused”, and he called out, “PET-CT is not for health checkups!” He once asked many doctors, “Would you let your healthy family members go for a PET-CT physical examination?” The answer was usually “no”. Public personal acceptance of radiation standards regarding ionizing radiation, the United Nations Scientific Committee on the Effects of Atomic Radiation report pointed out that the average annual radiation dose to individuals from natural background radiation is about 2.4 mSv (mSv stands for millisieverts). And certain high background areas in China 3.70mSv/year.ICRP (International Commission on Radiological Protection) recommended limits, in order to prevent stochastic effects, stipulate that the annual dose equivalent of a radioactive worker exposed to whole-body homogeneous irradiation should not exceed 50mSv, and that the annual dose equivalent of an individual in the public who is exposed to irradiation should be less than 5mSv.In recent years, with the widespread use of CT, the perfusion CT examination of the measured public has been increasing more and more. It is incorrect to say on the Internet that the radiation dose received from one CT examination is equivalent to the dose of many chest radiographs (some say more than 200). Modern new high-grade CT machine and the early years and even ordinary spiral CT machine on the patient caused by the radiation dose is certainly a big difference, that is, the difference in equipment; the different methods of examination, but also so that the dose received is different (above has been talked about); age differences, that is, children to be more sensitive than adults to the rays; different parts of the human body and different organs on the ray of the sensitivity of the more different (see the following chart), the sensitive, that is, there may be harmful. For example, the skin is not sensitive, the gonads and other organs are sensitive; in addition, there are individual differences, i.e., the sensitivity of people to radiation is also different from person to person. The following dual-source spiral CT a coronary angiography examination as an example, to illustrate that the dose of the new modern CT examination is very small, there is no need to do one or two times for the CT and panic. This is Siemens CT application experts recently a phase of the study, which, for example, the use of dual-source spiral CT for coronary angiography (120KV, 35mA) the patient receives a dose of 0.18mSv calculated by a special formula, only equivalent to the new X-ray equipment ingested 2 times the dose of the chest film (according to each chest film, the patient receives a dose of about 0.1mSv). As can be seen from the above, at present, although the reasonable radiological examination done by the medical treatment is safe, however, if many times during the year, repetitive examination (or worse, repeated examinations within a month), is bound to produce the cumulative effect of radiation hazards (especially sensitive areas), if the diagnosis of the disease really need to save life and cure the disease in the first place, but also is no choice. However, attention should be paid to: 1) not to abuse or blindly repeat the examination; 2) try to use radiation-free examination; 3) try to avoid radiation-sensitive organs, such as the eyes, thyroid, gonads, mammary glands. Children try to avoid unimportant CT or X-ray examinations