“Radiation”, which is invisible and untouchable, but closely related to our lives, often causes a lot of people to panic. For example, last year, after the Fukushima nuclear power plant accident in Japan, people worried about the health effects of radiation, and even triggered a “salt rush” trend, which was constantly teased on the Internet. When we go to the hospital, we will also encounter “radiation” related tests and treatments. For example, we usually have a medical checkup and need to take an X-ray chest film or do chest fluoroscopy. Outside the examination room, we can see a prominent radiation warning sign, the doctors do not stay in the examination room more, are sitting in the next shielded room. Many people have questions about the safety of these “radiation” tests. What is radiation? First of all, let’s understand what radiation is. 1, usually harmless “radiation” “radiation” is the common name of electromagnetic waves, it is everywhere: wavelength of 390 nanometers to 700 nanometers of electromagnetic waves commonly known as “visible light”, it is a kind of radiation; wavelength of 760 nanometers to 1 mm wavelength range of electromagnetic waves commonly known as “heat”, it is also a kind of radiation; we have to use every day microwave oven, the use of electromagnetic waves of the thermal effect, or a kind of radiation. Except for too close to the heater will be burned, or stuff yourself into the microwave oven will burst these cases, these kinds of radiation usually do not cause damage to living organisms. 2, may threaten the health of the “radiation” Another type of radiation, known as “ionizing radiation”, this is what we really need to care about. The reason why it is called “ionizing radiation” is because this kind of electromagnetic wave penetrates strongly, and when it reaches a certain energy, it can directly “break” the chemical bonds of biological macromolecules, which may cause damage to human cells. In ionizing radiation, except for ultraviolet rays from the sun, we can easily come into contact with other things such as X-rays and gamma rays, only under special circumstances, we have the opportunity to be exposed to large doses. Medical radiation: very low risk So many kinds of ionizing radiation, are they all safe for humans? Let’s get to the point from here. 1, radiation dose Because different kinds of radiation energy varies, and different body tissues absorb different amounts of radiation, in order to facilitate quantification, people have defined a unit called Sivot (Sv), to illustrate the amount of radiation absorbed by different biological tissues. By definition, the amount of radiation in 1 Sv is equivalent to the absorption of 1 Gorey (Gy, i.e., joules/kilogram) of radiation by a tissue. In practice, this unit dose is too strong and is equivalent to the level of nuclear radiation dose absorbed by the survivors of the Hiroshima atomic bomb back then. Therefore, medical science generally uses millisievert (mSv) to measure the hazard, 1 Sv = 1000 mSv. There is a low amount of background radiation in nature, each person will have about 3 mSv of background radiation absorption per year, which is a good reference indicator. 2. Types of medical radiation Among the routine examinations in hospitals, ultrasound and magnetic resonance imaging (MRI) are non-ionizing radiation examinations, while X-ray and CT examinations produce ionizing radiation. In addition, there are some examinations such as “single photon imaging” and “positron imaging”, which are less common nuclear medicine treatment methods and also produce ionizing radiation. 3. The effects of medical radiation doses on the body As for the possible effects of radiation of mSV magnitude on the body, only the point of “causing cancer” should be considered. Theoretically, the damage caused by radiation is completely random; if the radiation dose is too high, the chance of damage to cellular DNA, which is responsible for critical biological functions, is greatly increased. Under the influence of radiation, DNA may break and lose its function, or it may mutate. Although DNA has its own repair system, as the amount of damaged DNA rises, so does the amount that has no chance of being repaired. If a DNA mutation happens to land on an oncogene and flips the switch for cellular malignancy, then, at some point down the road, the body could develop a tumor. In fact, there is very little research data on exposure to high doses of radiation, the vast majority of which comes from studies of Japanese nuclear bomb survivors. Therefore, it can only be clearly concluded that the probability of cancer in human body will be significantly increased only when exposed to radiation doses of 100 mSv or more. 4. How much radiation can be caused by a medical examination? Besides looking at the radiation doses for specific examinations in the table, let’s take a concrete example. CT examination is one of the most used clinical examinations and the radiation dose is relatively strong. For example, a CT scan of the abdomen brings a radiation dose of about 10 mSV. This radiation dose is equivalent to the “background radiation” that we accumulate in our daily environment for 3 years, i.e., the amount of radiation we receive without doing anything special. Within the dose range of 10 C 100 mSV radiation from CT, some studies suggest that it may increase the chance of developing cancer in the long term, while others suggest that it may not. As for the carcinogenicity of radiation doses below 10 mSv, it has only been inferred through mathematical models that accumulation of a certain amount of radiation may have an increased risk of distant cancer. However, hundreds of millions of people worldwide have been examined with doses of ionizing radiation below 10 mSv in the last few decades, with absolutely no epidemiological data to suggest that these examinations are risky. We already know that the radiation doses from conventional radiography are quite low and can be considered completely safe. CT exams are subject to higher radiation doses, which may even reach risk doses of 10 mSv or more. However, CT exams are ordered by physicians, often when a major illness is suspected and no alternative is available. As with other treatment and screening options, the choice to have a CT exam is a trade-off between the pros and cons. In the early days of radioactivity, there were many tragic incidents due to failure to prevent it, and later, nuclear weapons and accidents caused a great deal of psychological shame; therefore, the medical community is still cautious about such technology as CT. It is important to tell your doctor if you have had an examination with ionizing radiation in the near future to avoid accumulating radiation doses from repeat CT examinations. After weighing all the pros and cons, medical consideration is also given to special care for special populations: pregnant women and children should be exposed to as little radiation as possible. When pregnant women and children are exposed to radiation, protective measures such as lead plates are placed in sensitive areas such as the abdomen; in addition, advanced instruments have methods to reduce the amount of radiation exposure (ASIR technology). For example, if a pregnant woman or child is suspected of having pneumonia and undergoes a chest x-ray, the radiation dose given in the table (0.1 mSv) is within a very safe range, and the placement of a lead plate on the abdomen reduces the risk to 0. Older fluoroscopy equipment (7.0 mSv) is still occasionally seen in China, and for medical examination purposes it is possible to avoid fluoroscopy in favor of x-rays.