A metal artefact is an image disturbance that appears during radiological examinations such as X-ray, computed tomography (CT), or magnetic resonance imaging (MRI) when metal is present in the body.
How does a metal artefact form?
When metal is involved in an examination, for example from dental implants, artificial joints, screws after an operation, or other prostheses, it can significantly affect the imaging. The technology behind X-ray, CT, and MRI works by detecting how differently dense materials in the body, such as bones, soft tissue, or air, respond to the relevant rays. Metal, however, is so dense and deflects the rays so strongly that it causes disturbances in the image. These disturbances appear as bright or dark streaks, shadows, distortions, or blurred areas that are not actually present in the body.
What do metal artefacts look like?
In an image, metal artefacts often appear as ray-like lines, bright spots, or broad shadows spreading out around the metal. These effects are particularly common with dental fillings, artificial hip joints, or screws used after bone fractures. The affected areas can sometimes not be assessed properly at all, because the structures behind or beside them are obscured by the image disturbances. This can look, for example, as though a white beam is coming from the metal, or as though part of the image is completely blurred.
Why are metal artefacts a problem?
These image disturbances make it harder for radiologists to recognise important details. Particularly when it comes to detecting inflammation, tumours, or other changes near metal implants, metal artefacts can make a diagnosis uncertain. Sometimes the area behind the metal is so severely disturbed that no conclusion can be drawn about the condition of the tissue there. This affects not only the immediate surroundings of the metal, but can also have an impact on areas of the image that are further away.
What can be done about metal artefacts?
Modern equipment and specialist image processing methods now help to reduce the effects of metal artefacts. In CT, for example, there are special algorithms that calculate out such disturbances and improve the image afterwards. In MRI, different measurement methods are often chosen, or so-called metal artefact reduction sequences are used. Even so, it is not always possible to fully restore the image quality. In some cases, it may be sensible to switch to a different examination method, or to remove the metal temporarily if this is medically acceptable. This is rarely possible, though, and mainly applies to small items of jewellery or piercings.
Are there differences compared to other artefacts?
Metal artefacts are just one form of image disturbance in radiology. There are other types as well, such as susceptibility artefacts, which occur mainly in MRI and are related to differences in the magnetic behaviour of tissues. Artefact superimposition is another term that describes image errors where several different disturbances occur together and distort the image further.
When are metal artefacts to be expected?
Whenever metal is present in the examination field, these artefacts can occur. This is particularly common with dental prostheses, artificial joints, screws, plates, or pacemakers. Even small metal items such as piercings or tattoo inks containing metallic components can cause image disturbances. Before an examination, patients are therefore often asked whether metal is present in the body. This helps the medical team to plan the examination more carefully and, where necessary, to take steps to reduce the artefacts.
What does this mean for the reliability of the examination?
A metal artefact does not mean that the entire examination is unusable. Many areas often remain clearly assessable. However, it is possible that important details are lost precisely where the metal is located. The medical team then checks whether the available images are sufficient or whether further examinations are needed. In many cases, enough information can still be gathered despite artefacts to make a reliable diagnosis. If not, other imaging methods such as ultrasound can offer an alternative, as they rely on sound waves rather than rays or magnetic fields.
What should you do if metal artefacts are mentioned in a report?
If a medical letter or report states that metal artefacts are affecting the image quality, this usually means that certain areas in the image could not be assessed clearly. This is no cause for concern, but rather factual information for the treating doctors. It tells them that they need to take this limitation into account when planning further treatment. For patients, this generally means no danger, but simply that the image is less informative in certain areas.
Connections with other terms
In medical imaging, various types of artefact appear that differ in their cause and appearance. Alongside metal artefacts, there are, for example, susceptibility artefacts and artefact superimpositions, each of which has its own particular features.
Metal artefacts are therefore a typical side effect of modern imaging when metal is present in the body. They can sometimes be a challenge for diagnosis, but thanks to technical advances and the experience of radiologists, they can often be assessed well and in many cases at least partially corrected.
