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Computed tomography. What is important to know.


It is not enough for a modern doctor to simply look at the patient and learn about his well-being. A comprehensive diagnosis is required, sometimes additional studies to determine the state of the body.

When the doctor prescribes blood tests, which must be repeated several times during the illness, to determine the individual dose of the drug or to monitor the patient's vital signs, no one has any concerns or questions about how dangerous this is. And when prescribing X-ray diagnostic tests, many patients have fear.

However, it should be understood that making an accurate diagnosis without X-ray diagnostic studies and objective control of the dynamics of the course of the disease and the effectiveness of treatment in the absolute majority of cases is impossible.

How harmful is X-ray radiation and should we be afraid of it?

To account for the radiation dose received by a person, the Sievert unit is used. 

Since 1 Sievert is a very large dose, the actual measurement results include millisievert (mSv) (1/1000 Sievert), or even microsivert (mSv) (1/1000000 Sievert). 

Sievert is the total radiation dose of the human body. The absorbed dose in Sieverts is calculated separately: 

  • as equivalent (natural radiation and the proportion of artificial radiation),
  • effective,
  • and the organ dose (taking a picture of the hand is less dangerous than the head or genitals).

Medical X-ray examinations are not the only source of radiation for humans, they account for about 30%, and 70% is accounted for by the natural sources of radiation that surround us in nature.

Background radiation

We are all constantly exposed to natural background radiation. For our country the average background dose is about 2 mSv in a year; for countries where a lot of granitic rock (France, Finland, Sweden, the coastal area of the South-West of India, some resorts Brazil, etc.), natural background – 3-5 times, but they are not observed surge of oncological diseases and moreover, many areas with high radiation background are recognized resorts (for example, Finland, Caucasian Mineral Waters, Karlovy vary, etc.).

So, the average global background radiation dose is 2.4 mSv per year – the average amount of radiation received by 1 person for 1 year of living on Earth; up to 1 mSv per year is an additional dose of radiationthat a person can receive during the year due to flights and medical research. In total, on average, we receive about 3.4 mSv of radiation per year. At the same time, the factor of place of residence remains important for taking into account the background dose.

What is the radiation dose for X-ray diagnostic studies? 

This depends on the X-ray equipment, the examination performed, and the anatomical features of the patient.

Modern digital devices and new CT protocols have not only improved the quality of diagnostic images, but also significantly reduced the dose due to technology.

Computed tomography (CT)) – this is a method of layer-by-layer diagnosis of the body, based on X-ray radiation. Modern computer tomographs are multi-spiral devices. 

CT is currently the leading method of diagnosing many diseases:

  • the brain,
  • the spine,
  • lungs and mediastinum,
  • liver,
  • kidneys,
  • pancreas,
  • the adrenal glands,
  • aorta and pulmonary artery,
  • the heart and a number of other organs. 

CT can be used both as a method of primary diagnosis, and as a clarifying techniquewhen a preliminary diagnosis has already been made using ultrasound or clinical examination.

Are there any contraindications?

There are no absolute contraindications to CT
The method can be performed to the patient in any condition (even with artificial lung ventilation). The study is associated with a small radiation load, but when examining pregnant women and young children, it is necessary to carefully weigh the need for CT in each specific case. If a breast-feeding mother needs a CT scan, there is no need to interrupt breastfeeding or express milk – X-rays do not affect its composition.


The issue of dose loads is regulated by lawResolution of the Chief State Sanitary Doctor of the Russian Federation of 07.07.2009 No. 47 " On approval of SanPiN "(together with " NRB-99/2009. SanPiN Radiation safety standards. Sanitary rules and regulations". SanPiN ionizing radiation, radiation safety).

The maximum effective dose for the population is 1 mSv per year on average for any consecutive 5 years, but not more than 5 mSv per year

However, the same document states that medical procedures involving the exposure of patients should be justified by comparing the diagnostic or therapeutic benefitsthey bring with the radiation damage to health that exposure can cause. 

Also, the patient has the right to refuse medical radiological procedures, with the exception of preventive studiesconducted in order to detect diseasesthat are dangerous in epidemiological terms, the limits of radiation doses of patients with diagnostic purposes are not established.

Thus, if the doctor understands that performing a CT scan is critical for evaluating the effectiveness of treatment, and failure to perform this study can lead to fatal consequences for the life and health of patients, then he should prescribe this study. However, despite the established maximum allowable annual value, it is not recommended to exceed the indicator of 50 m3b .

You must remember:

  • the effect of X-ray radiation on the human body ends immediately after the completion of the examination;
  • by themselves, the rays do not have the property of accumulating in the body;
  • they do not lead to the formation of radioactive substances, so you simply do not need to remove anything from the body.

Dear patients!
Treat with confidence and understanding the appointment of X-ray diagnostic tests. Remember that the doctor when prescribing them always proceeds from concern for your health and the commandment about not harming your patient.

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GBUZ Moscow Clinical Scientific Center named after Loginov MHD