During computed tomography, the radiation causes a high radiation exposure. Compared to X-rays, this radiation exposure is particularly high and therefore more dangerous than an X-ray examination. Nevertheless, computed tomography (CT for short) offers many advantages over X-rays.
On the one hand, cross-sectional images of the body can be taken, and on the other hand, organs and soft tissues are shown much better than would be possible with X-rays. Due to the high radiation exposure, people often try to switch to magnetic resonance imaging (MRT). Magnetic resonance imaging can also produce sectional images of the body without any radiation exposure.
However, depending on the image, it may take a long time to obtain an image using magnetic resonance imaging. Computer tomography, on the other hand, takes only a few milliseconds. In addition, computer tomography allows contrast medium to be injected into the vein, which makes it easier to distinguish between two organs or two tissues.
Nevertheless, there is always the risk of high radiation exposure in computed tomography. Each patient receives an average radiation dose of about 4 mSv per year (mSv=millisievert, the unit in which radiation dose, i.e. radiation exposure, is given). If a patient now receives a whole-body CT, i.e. an image of his or her entire body taken by means of computed tomography, this corresponds to an exposure of 10-20mSv.
This means that the radiation exposure from a single computer tomography image exceeds the average annual value by a factor of 3-5. For this reason, a full-body CT scan is only taken in very rare cases, for example, when a tumour focus is being looked for but could not be found using magnetic resonance therapy. More often, however, a CT of the abdomen is performed.
Here the radiation exposure is 8.8-16.4 mSv. This corresponds to twice to four times the dose of radiation that a patient would normally “collect” within a year. The radiation exposure is not quite as high when the chest (thorax) is exposed.
In this case, the radiation exposure from the computer tomography image is 4.2-6.7mSv. This corresponds approximately to the annual dose of a patient. Often a computed tomography image of the lumbar spine is also taken, especially in patients with a suspected herniated disc.
Here the radiation exposure is about 4.8-8.7mSv. But especially because of the alternative of the MRI ́s a CT should be well considered in case of a herniated disc. The data of the radiation exposure always fluctuate quite strongly, because it depends on how strong or how thin a patient is built.
In the case of a particularly obese (thick) person, a higher radiation dose and thus a higher radiation exposure must be applied so that the radiation can also pass through the fat to the organs. Even 4 kg overweight means a significantly higher radiation exposure. In slim people, on the other hand, the radiation can penetrate directly to the organs without major obstacles, so the radiation dose does not have to be particularly high.
Computer tomography is frequently used, especially for examinations of the head. The advantage is that, especially in the case of a stroke (apoplexy) or bleeding into the brain due to a vein or artery rupture, this is detected within a few seconds. The disadvantage is, as always with computed tomography, the radiation exposure in and around the head. An examination of the head leads to a comparatively low radiation exposure with only 1.8-2.3mSv. This corresponds approximately to the radiation exposure of half a year.
