Computed tomography (CT) is an imaging technique that uses X-rays to create cross-sectional images of the human body.
In the CT machines used today, the patient is moved on a couch through an approx. 70 cm wide ring (gantry). This ring contains an X-ray tube and a detector opposite it. As they rotate together, the patient's body is X-rayed from different directions.

The CT image is created by reconstructing many individual absorption beams from the X-rays sent through the body from different directions.
The different levels of absorption are due to the different tissue composition, e.g. bone tissue is very radiopaque and therefore absorbs a lot of radiation and appears bright (hyperdense) on CT images, while lung tissue absorbs almost no radiation due to its high air content and is therefore dark (hypodense) on CT images.
The detector converts the incoming, transmitted radiation into electronic signals. Using this data, the computer calculates the absorption value for each point, which then generates slice images (known as tomograms) and, if necessary, a three-dimensional representation is created based on the composition of the individual slice images.

The tissue of the brain is relatively homogeneous in terms of X-ray density, so that changes in the brain become visible due to poorer contrast between the two main types of tissue, grey matter (nerve cells) and white matter (nerve fibres).
As CT achieves valid results in a time-saving manner, these examinations are used in clinical diagnostics, particularly for acute changes in the brain, for example to detect a blood haemorrhage or a stroke. However, due to the radiation exposure associated with health risks, their use is limited to medically indicated examinations.