Some things you may not know about CT radiation!

Author: Zhang Tian China Rehabilitation Research Center

Reviewer: Chen Zhenbo, deputy chief physician of China Rehabilitation Research Center

What? Eating bananas also causes radiation? Yes, you read that right. Eating bananas also causes radiation. Because bananas contain potassium, each banana you eat will be exposed to about 0.1 microsievert (μSv) of radiation. Seeing this, you may be worried. Eating bananas causes radiation. So, can you still eat bananas in the future? As the saying goes, "It is nonsense to talk about toxicity without considering the dose." To reach a lethal dose of radiation, you need to eat 20 million bananas. Radiation is everywhere in our daily lives. The stones, soil, building materials, and cosmic rays in our living environment all have radiation, but the radiation dose is very small and has no effect on health.

So what exactly is radiation?

Radiation is divided into non-ionizing radiation and ionizing radiation.

Non-ionizing radiation refers to low-energy electromagnetic waves, also known as electromagnetic radiation (also called electronic smog, electromagnetic waves), such as ultraviolet rays, visible light, infrared rays, microwaves, radio waves, etc. Computers, microwave ovens, radios, TV signals, and mobile phone signals commonly used in daily life are all electromagnetic waves. Non-ionizing radiation is generally harmless and there is no need to worry too much.

Ionizing radiation used in the field of radiation medicine and protection mainly refers to alpha particles, beta particles, gamma rays, including some protons, X-rays and other uncharged or charged particles or light waves. The working principle of CT (computerized tomography) mainly relies on the penetration, photosensitivity and fluorescence of X-rays. It is dangerous to living things and can ionize atoms or molecules of substances to form ion pairs (ions and electrons). Excessive ionizing radiation can destroy certain macromolecular structures of the human body, causing cell damage and even DNA damage.

Seeing this, you may ask again: "If it is harmful, do we still need to do CT scans? Will I get leukemia or cancer after doing a CT scan?"

In fact, although ionizing radiation can change the properties of biological macromolecules in the human body, it does not mean that as long as the human body is exposed to ionizing radiation, it will cause damage to the human body or even cancer. The degree of damage to human health depends on the intensity of the radiation and the time of exposure to radiation. Therefore, there is no need to worry too much and be afraid of radiation.

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Next, let me introduce you to the radiation dose of CT examinations of various parts of the body.

First of all, we need to understand what radiation dose is. Radiation dose is calculated based on the radiation energy absorbed by human tissues and organs per unit mass. The commonly used unit is millisievert (mSv). The main unit of radiation dose is sievert (Sv), but sievert is a very large unit, so millisievert (mSv) is often used, 1mSv=0.001Sv. The radiation dose varies depending on the patient's examination items and examination parts. The radiation dose of CT examination is roughly as follows (CTA stands for arterial CT angiography):

(1) Plain scan of the head, the radiation dose is approximately equal to 2 mSv.

(2) Chest CT scan, radiation dose is 6 to 8 mSv.

(3) A low-dose chest CT scan can reduce the radiation dose by at least half, to 3 to 4 mSv.

(4) Plain scan of the abdomen with a radiation dose of 15 to 20 mSv.

(5) Coronary CTA examination: radiation dose is 5 to 15 mSv.

(6) The radiation dose of whole aorta CTA examination is relatively high and may reach 30mSv.

my country's radiation protection standards stipulate that the annual equivalent dose of radiation exposure to a single tissue or organ of the public should be less than 50mSv. Therefore, as long as you pay attention to radiation protection during CT scanning, use protective equipment such as lead clothes and lead neckbands to reduce X-ray exposure, and try to avoid repeated CT examinations, you can minimize the harm of radiation. In other words, as long as the total radiation dose received is controlled within the safe value range, it is safe.

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Is there any way to reduce radiation?

Of course, the following methods can help us reduce radiation dose:

(1) Do not over-examine. CT examinations have advantages and disadvantages. We only need to do it when the advantages outweigh the disadvantages. If a problem can be solved by plain scanning, we do not have to choose enhanced scanning, because the more and more complex the examinations are, the greater the radiation dose will be.

(2) The protection provided during the examination, including radiation protection for some sensitive organs such as the thyroid gland and reproductive system, will also reduce radiation.

(3) Be sure to cooperate with the examination as required. If the examination requires breathing, be sure to cooperate with breathing. If the examination cannot move, be sure not to move, to avoid unnecessary repeated examinations.

(4) Try to remove clothes and accessories that may affect the examination, and make preparations for the examination as required, especially diet control and intestinal preparation.

(5) If you have undergone an enhanced CT scan with contrast agent, you can drink plenty of water after the examination to increase the excretion of the contrast agent. You can also eat some anti-radiation fruits to reduce the impact of radiation, such as carrots, broccoli, tomatoes, apples, etc.

(6) Use high-end equipment. The radiation dose of the most advanced equipment may be only 30% to 50% of the conventional CT dose, or even lower.

(7) MRI and B-ultrasound do not cause radiation and can be used instead of CT examinations.

What about pregnant women and children who need to be examined?

Although the radiation dose of medical X-rays to the human body is very small each time, reproductive cells or fertilized eggs can be easily damaged.

Women should generally undergo X-ray examinations within 10 days after menstruation, and should not undergo this examination during ovulation or early pregnancy, because the embryo and fetus are very sensitive to radiation. In particular, pregnant women are prohibited from undergoing radiological examinations in the early stages of pregnancy. In addition, if a couple undergoes a pelvic radiological examination during the pregnancy preparation period, it is recommended that they wait three months before becoming pregnant for safety reasons.

Children with fever and cough should be given priority for chest X-ray examination. The average radiation dose of a chest X-ray is 0.01-0.02 mSv, and at least 5,000 shots are required to reach the dose that increases the risk of cancer. Therefore, there is no need to worry too much about routine physical examinations and tests for children. However, CT examinations have a higher dose than ordinary X-rays, so is it safe for children to have CT examinations? If children must choose CT examinations, there is no need to worry too much. Children's radiation dose is lower, about 1/5 of that of adults, which is far below the national safety standard. Therefore, children's CT examinations are within a safe dose range.

What we really need to pay attention to is another source of radiation - secondhand smoke

Cigarettes contain radioactive substances that can release alpha rays. If an adult smokes a pack of cigarettes (20 cigarettes) a day, the annual radiation is approximately 8.7 mSv. For a child who is exposed to secondhand smoke, this is equivalent to at least 435 chest X-rays!

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In general, although CT examination has certain radiation effects on the human body, it is still the most common and powerful examination method for many diseases. When undergoing CT examination, you don’t have to worry too much. You can follow the methods taught by the author to reduce radiation damage.