What are beam hardening artefacts?
Beam hardening artefacts are image distortions that can occur during certain imaging examinations such as computed tomography (CT) and affect the accuracy of the scan. They happen when X-rays pass through very dense structures like bone or metal and are absorbed at different rates. This causes parts of the final image to appear brighter or darker than the actual tissue structure really is.
How do these image errors occur?
During a CT scan, the body is examined using X-rays. Different types of tissue, for example bone, muscle, or organs, absorb the rays to different degrees. Very dense material such as bone or dental implants absorbs much more radiation than soft tissue. The CT software then uses this information to build up an image.
When an X-ray beam passes through very dense areas, the rays that come out the other side are heavily filtered. The lower-energy rays are absorbed more strongly, leaving mainly the harder, higher-energy rays behind. This effect is called "beam hardening" because the range of rays shifts towards higher energy. As a result, the CT scanner misreads the affected areas, and so-called beam hardening artefacts appear in the image as streaks, shadows, or bright patches.
Where do beam hardening artefacts most commonly occur?
These image distortions are most often seen where very dense and less dense layers of tissue lie directly next to each other. Typical examples include the skull area, where solid bone sits alongside the brain, or the jaw, where dental fillings and implants are present. Large metal objects, such as artificial hip joints or surgical screws, can also cause pronounced artefacts.
In a CT image, these artefacts usually appear as ray-like lines or blurred, distorted areas around the dense structures. This can make it difficult or even impossible to assess the surrounding tissue properly.
What do beam hardening artefacts mean for the examination?
When reviewing a CT scan, it is important to understand that beam hardening artefacts are not real signs of disease. They are purely technical image errors. However, they can make certain areas harder to assess. This may mean that small changes in the tissue are missed or are difficult to tell apart from the artefacts.
Radiologists are trained to recognise these image errors and to take them into account when writing their reports. In many cases, special post-processing techniques or different scanning methods can help reduce the effects of the artefacts. Modern CT scanners also have special algorithms that are designed to correct these kinds of distortions.
What can make artefacts worse?
Certain factors increase the likelihood of beam hardening artefacts. These include metal objects in the area being scanned, such as dental braces, prosthetics, or surgical implants. Very large bones, such as those in the pelvis or skull, can also cause noticeable distortions. Depending on the purpose of the scan and the area being examined, it may be worth checking beforehand whether any metal objects can be removed or whether other steps can be taken.
What does this mean for the result of the examination?
Beam hardening artefacts are a well-known challenge in medical imaging, but they are not dangerous and should not be confused with a medical condition. They simply indicate that part of the image has been technically distorted. The reliability of the examination may be reduced as a result, which is why radiologists pay particular attention when reviewing affected scans. If needed, additional examinations may be recommended to ensure a clear and confident diagnosis.
