The annual effective dose of natural radiation to China residents is () msv.

The amount of radiation is harmful to human body. Everyone must know that radiation is harmful to human body, but there are actually many kinds of radiation. Different kinds of radiation will cause different hazards. There is also some radiation in daily life. The following shared radiation is harmful to human body.

How much radiation is harmful to human body 1? Let's see what radiation is.

Radiation is divided into ionizing radiation and non-ionizing radiation according to the level of energy and the ability of charged substances.

Ionizing radiation has high energy and frequency, which can ionize the affected substances, such as cosmic rays, X-rays and radioactive substances. This process will cause pathological changes of organs and systems in the body, cause systemic reactions of the body, and cause harm to the body.

Non-ionizing radiation has low energy and will not ionize substances. Including ultraviolet rays, mobile phones, computers, induction cookers, high-voltage lines, substations, television broadcasts and other electromagnetic fields, the harm is weak.

? What radiation does the hospital use for filming?

Hospital X-ray fluoroscopy, photographic diagnosis, radionuclide determination of human organs, tumor radiotherapy, etc. It's all ionizing radiation

The list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization has been preliminarily sorted out for reference. Ionizing radiation (all types) is in the list of carcinogens.

It's scary and carcinogenic at first glance. You said the risk is extremely low? Isn't this a bluff?

In fact, people are exposed to natural radiation all the time in their lives, which is called natural background radiation. The radiation a person receives is usually around 2.0mSv-3.0mSv/ year. According to scientific statistics, the average annual effective dose of natural radiation in the world is about 2.4mSv.

Millisieverts (mSv) are usually used to measure radiation hazards in medicine. Only when the radiation dose is above 100mSv will the probability of cancer increase significantly.

? What is the radiation of CT, MRI and B-ultrasound?

In fact, a certain degree of radiation in the hospital will not cause harm to the human body. It's nonsense to talk about radiation damage without dose.

The harm of radiation to human body depends on the total radiation dose of CT examination. If repeated examinations are carried out within a certain period of time, such as cancer patients, after repeated examinations/reexaminations and multiple scans of images, the accumulated radiation dose will increase, which is definitely harmful to the human body.

Let's take a look at the radiation of B-ultrasound, X-ray, magnetic vibration and CT:

? type-B ultrasonic

Radiation: None

The principle of B-ultrasound is to use ultrasonic waves to penetrate the human body. When sound waves meet human tissues, they will generate reflected waves, which are imaged by calculation. It is mostly used for prenatal examination during pregnancy to check the fetal condition. There is no radiation risk in the inspection project of "Ultrasound Department", so don't worry about radiation.

? MRI

Radiation: None

It was originally called "nuclear magnetic vibration", but when I heard that there was "nuclear" in it, I always misled everyone into thinking that there was radiation. In the magnetic field, atoms (mainly hydrogen atoms) in the subject vibrate, and then receive the energy of this vibration for imaging. There is no radiation from magnetic vibration. In order to avoid misunderstanding, it has been renamed as "Magnetic Vibration Inspection".

? x ray film

The radiation is very small, 0. 1mSv.

Because X-rays will be absorbed in different degrees when passing through the human body, for example, the amount of X-rays absorbed by bones is more than that absorbed by muscles, so the amount of X-rays after passing through the human body is different, so shadows with different densities will be displayed on the fluorescent screen or photographic film (after development and fixation).

The radiation dose received in a chest X-ray examination is 0. 1mSv, which is roughly equivalent to the radiation dose received in daily life 10 day.

? CT examination

High radiation 2- 15mSv.

The principle of CT examination is that X-rays will pass through the human body layer by layer and be imaged twice after computer calculation, just like cutting a piece of bread into pieces.

The radiation of CT examination is related to dose. Take an ordinary chest CT as an example, the radiation dose during examination will not exceed 1mSv, which is equivalent to the high-altitude radiation when we fly from Guangzhou to Beijing.

Chest X-ray is about 1. 1mSv, chest X-ray dose is 0.2mSv, skull CT 2mSv, chest CT 8mSv, abdomen CT 10mSv, pelvis CT 10mSv.

For example, the radiation dose of flying 10000 km (about 20 hours) is about 0.05mSv, and the radiation dose of an X-ray examination is 0.02-0. 1mSv, which is equivalent to flying for 20 hours; The radiation dose of a common chest CT examination is 2mSv-5mSv, and the daily radiation dose of 1 pack of cigarettes is 0. 1mSv, which is equivalent to smoking twenty or thirty packs of cigarettes. In other words, the amount of radiation a person receives by flying and smoking in a year is much more than an X-ray or ordinary CT chest examination.

? Nuclear medicine examination PET/CT

The radiation is higher, 15mSv.

The full name of PET-CT is positron emission computed tomography (PET-CT), which is an advanced imaging technology for clinical examination in the field of nuclear medicine. PET-CT integrates PET and CT into a complete imaging system, which is called integrated PET-CT system. Patients can obtain CT anatomical images and PET functional metabolism images at the same time through rapid whole body scanning during examination. The advantages of the two images are complementary, so that doctors can get accurate anatomical location while understanding the information of biological metabolism, so as to make a comprehensive and accurate judgment of diseases, such as benign and malignant tumors.

The primary radiation dose of PET-CT is generally between 10 millisieverts-15mSv in China, which is equivalent to the primary radiation dose of chest CT, and will not cause harm to human body, but it has a disadvantage that the examination cost is expensive.

From this point of view, the image examination of the above hospitals is far from reaching the radiation value of 100mSv, which is not harmful to our health. However, if you receive high-dose radiation in a short period of time, or receive low-dose radiation for a long time, it may indeed lead to cell mutation and physical lesions.

The amount of radiation is harmful to human body. The propagation of any energy in space is called radiation, including all kinds of electromagnetic waves. Radiation related to nuclear energy will do harm to human body, which is also called ionizing radiation and radioactive radiation, that is, radiation that can ionize substances, including X-rays, gamma rays (all high-energy photons), protons, alpha radiation, beta, beta+radiation, fission fragments (all charged particle radiation) and neutrons.

The standard to measure the harm of radiation to human body is how much radioactive energy people absorb. Different types of radioactivity and the same energy cause different harm to organisms. The following table shows the effective biological dose weights of different radiation types:

The energy absorption unit is Gory (absorbed dose), and 1 Gory is equal to 1 kg. The material absorbs radiation energy of 1 joule. The damage to organisms is measured by relative bioavailability (RBE), and the unit is Sewart. According to the above table, if the radiation type is X-ray, electron, etc. Then 1 Gray is equal to 1 Silver. If it is an alpha particle, 1 gray is equal to 20 sieverts.

Different parts of the human body are also sensitive to radiation damage, and gonads (germ cell generation areas), bone marrow, breast, thyroid and other areas are sensitive to radiation and vulnerable to damage.

Under natural conditions, air, human body, land and buildings all have radioactive radiation, which is called background radioactive radiation. The average annual background radiation received by human body worldwide is 2.4 millisieverts, with slight differences in different regions, such as about 3 in North America and 1.5 in Australia. The recent background radiation in China is 3. 1, which is obviously higher than the global average level, which is related to the heavy industrialization, massive mining, coal mining and groundwater exploitation in China in recent decades.

The human body's tolerance to radioactivity is relatively low (the higher the animal, the lower the tolerance to radioactivity). Figure 1 shows the damage ability of different doses to human body. Some key facts:

1, radioactive radiation is harmful, the greater the dose, the greater the damage, and there is no safe value. "A certain amount of radiation is beneficial to human body" is groundless.

2. For cancer, the effects of radiation damage are cumulative.

3. Every increase in radiation damage 1 sievert (300-400 years of background radiation) will increase the probability of cancer by 5.5% (absolute value, that is, if the original probability of cancer is 30%, it will increase to 35.5% after 5.5%).

4. In the facilities (environment) safety standards involving radiation damage, the extra radiation received by ordinary people should not exceed 5 millisieverts a year, professionals should not exceed 50 millisieverts a year, and five years should not exceed 100 millisieverts.

5. Acute radiation sickness (lymphopenia, leukopenia, nausea, vomiting, high fever, etc. ) If you are exposed to radiation above 100 millisieverts in a short time, it may happen.

6, short-term exposure to 3000-4000 millisieverts, 50% mortality within 30 days. The mortality rate of 6000-7000 millisieverts is 99.9%.

7. The internal radiation generated by radioactive elements absorbed into human body is far more harmful than external radiation, especially alpha radiation (the radiation on heavy ions such as radon, radium, uranium, thorium and plutonium and their decay chain elements is mainly alpha radiation). The radiation damage caused by alpha radiation with the same energy is 20 times that of beta and gamma radiation, while the energy of alpha particles is still four or five times that of beta and gamma particles. Therefore, in the case of internal irradiation, the damage caused by α decay is about 100 times that caused by β decay. Gamma radiation generally penetrates the human body, and the damage is much less.

Figure 1 Relationship between radiation damage and dose.

Microscopically, radiation can lead to protein's degeneration, DNA breakage, cytopathy or death. Most DNA damage will be repaired, but some can't be repaired. Irreparable DNA damage is DNA mutation, which may develop into cancer.

Some nuclear experts put forward that "moderate radiation is beneficial to human body", whose formal name is low-dose radiation excitation effect (radiation excitation effect, or steady state), that is, low-dose radiation can stimulate human immune system, promote human self-repair, and thus improve human health. This statement is possible without DNA mutation because cell death can stimulate the immune system. However, the probability of DNA mutation is directly proportional to the radiation dose and accumulates for life, so authoritative organizations responsible for formulating radiation damage standards, such as the United Nations Scientific Committee on the Effects of Ionizing Radiation (UNSCEAR) and the United States Radiation Protection and Measurement Committee, do not recognize this statement. The nuclear energy community, such as the website of the World Nuclear Association (WNA), strongly suggests that this statement makes sense. The linear threshold-free (LNT) theory recognized by authoritative organizations is called "hypothesis" in WNA. The French Academy of Sciences also has a report that partially supports this statement.

Figure 2. Relationship between radiation damage and dose. Line b is linear correlation, and line d is exciting effect.

Because radiation can damage DNA, organs with vigorous cell division such as gonads and bone marrow are more sensitive to radiation. Irradiation of these organs will cause infertility, leukemia and so on. For the same reason, pregnant women and children are more sensitive to the harm of radioactive radiation. When the fetus is damaged by radiation, the probability of lifelong cancer will rise. Especially because the brains of fetuses and babies are not fully developed, radiation damage will greatly reduce the IQ of newborns. Take the data provided by the US Centers for Disease Control as an example. If the fetus receives 500 millisieverts of radiation, the probability of lifelong cancer will increase from the average of 38% in the United States to 55%, and the IQ will drop 15 (please refer to the data of official website, the center for disease control in the United States: http://www.bt.cdc.gov/radiation/prenatal.asp).

How harmful is radiation to human body? Is the radiation from imaging examination harmful to human body?

In common imaging examinations, B-ultrasound and magnetic vibration are non-ionizing radiation, while X-ray, CT and nuclear medicine will produce ionizing radiation.

Ionizing radiation has strong penetrating power, and it will cause damage to human cells when reaching a certain dose, which is also the reason why people are afraid of imaging radiation.

The unit of ionizing radiation dose is mSv. In fact, people are exposed to different levels of radiation every day. For example, the radiation dose received after flying for 20 hours is about 0.1msv; ; A chest x-ray is about 0.2mSv；; The first dose of chest X-ray is about1.1msv; Smoke 1 pack of cigarettes every day and receive about 35mSv annual radiation. Subway security passengers may receive about one dose every year.

It's just that these radiation doses are not large and the harm can be ignored. Only when the radiation exceeds a certain dose will it cause certain health hazards to the human body.

Taking CT as an example, the radiation dose of a CT examination is about 2mSv- 15mSv, and the dose above 10mSv can be regarded as high risk.

At this time, people may be afraid and think, "Sure enough, CT will do harm to the body", but it is not, because doctors have weighed the pros and cons when deciding whether patients should have CT examination, and only when no other examination methods are feasible will they ask patients to have CT examination.

Although there are risks in CT examination, taking protective measures can minimize the risks. For ordinary people, there is no need to worry too much.

? Radiation dose sequencing of common imaging

In the hospital, we often see different impact tests, such as ultrasound, X-ray, ct, MRI and so on. Because of illness or different organs and parts. Many people often think, do these effects radiate? Is there a big difference in radiation?

? Let's classify them one by one to make them clearer:

B-ultrasound and nuclear magnetic resonance: no radiation, absolutely safe; X-ray photography (plain film): 0. 1MSV, the dose is very small and completely safe; CT: 2- 15 MSV, which is on the high side, but the radiation dose is within the safe range, so don't worry too much; Nuclear medicine examination SPECT: 0. 1-5.2 msv, small dose; Nuclear medicine examination PET/CT: The radiation dose of PET and CT is superimposed, and the maximum is only 15mSv. Generally speaking, the radiation generated by image inspection is within the safe range, so the subjects need not worry too much, but some people are not suitable for some of them!

? The following three groups of people should be cautious when doing CT examination.

The previous view of pregnant women was that during pregnancy, the development of the fetus was easily affected by various factors. At this stage, it is best for pregnant women not to do CT examination to avoid adverse effects of radiation on the fetus.

But now more and more studies show that a CT scan of any part of a pregnant woman's body has negligible impact on the fetus, but there may be problems with multiple scans.

However, the fetus exposed to radiation within 15 weeks before conception is slightly more likely to develop cancer in childhood, and its incidence rate is theoretically11000. However, this risk has not been confirmed for the time being. If the expectant mother is not at ease, she should explain to the doctor before the examination, adjust the radiation dose and prepare for radiation protection.

The child's body is in the development stage and his immune function is relatively low. CT scan is easy to affect the health of body cells, so it is best to avoid this kind of examination. If necessary, it is suggested that ultrasound, magnetic vibration and other non-radiation tests should be the first choice, or under the strict guidance and safety protection of doctors.

The contrast agent used in X-ray and CT examination of allergic patients is iodine, and about 4%- 12% patients will have allergic-like reactions after injection of contrast agent. There was a news report that a 60-year-old woman had contrast-enhanced CT scan in the hospital for a few minutes, and she was allergic to contrast media, nausea, chest tightness, palpitation, shortness of breath, weakness of limbs, unconsciousness and sudden drop in blood pressure. Finally, she was rescued and saved her life.

Therefore, people who are allergic to themselves should pay more attention to CT shock test and report their allergic history to the doctor in advance.

? There are so many kinds of CT, how to choose?

CT examination includes high resolution CT(HRCT), plain CT, low dose CT, enhanced CT, CTPA, etc. Whenever faced with so many kinds of CT examinations, patients often think that the most expensive is the best. In fact, ct examination is different only because of the needs of the patient's diseased part, organ and lesion size, not the more expensive the better!

For example, plain CT scan is one of the most common routine chest examinations in clinic. For HRCT, the resolution is low. Plain CT scan can only show 30-47.8% of HRCT, which is mostly used for routine examination in outpatient and emergency departments to find out whether patients have suspicious lesions.

If clues are found, the doctor may suggest using enhanced CT, focusing on the suspicious parts found after intravenous injection of contrast agent, thus improving the accuracy.

HRCT is mainly used to observe the fine structure of lesions and is a supplement to conventional chest scanning. HRCT can clearly show the fine structure of lung tissue, and its application in chest is very important.

Some people will think, why not use HRCT first? This is because HRCT can not replace conventional CT, but as a supplement to conventional CT. For today's patients, CT plain scan may be more suitable, and with the progress of examination, doctors will make further screening according to the patient's condition and with the change of examination methods, so that patients can have the most suitable examination.