Beam-hardening artifact
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Written from published radiology references and reviewed for plain language. Not written or signed by a physician, and not a diagnosis. How we write these pages →
In plain language
Dark streaks that fan out from something very dense on a CT — a hip replacement, dental work, a dense contrast pool. The streaks are a property of how X-rays pass through metal, and they obscure whatever they cross.
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Where you'll see this
CT findings, usually as an explanation of why one region could not be assessed.
Your report may word it “Streak artifact”, “Metal artifact” or “Beam hardening”. These mean the same thing.
Questions worth asking your doctor
- Was any part of the scan unreadable because of this?
- Does it need to be repeated, and if so how soon?
- Could this have hidden something, or only made the pictures look odd?
How often does this turn up?
Beam-hardening artefact is specific to CT and is seen constantly, particularly on scans of the head at the skull base, and anywhere near metal or dense bone. An X-ray beam is not a single energy, and as it passes through dense material the lower energies are absorbed first, so the beam that emerges is harder than the one that went in. The scanner’s reconstruction assumes otherwise, and the mismatch appears as dark streaks and bands.
Does it mean something is wrong?
It is a technical limitation rather than a finding, and its significance is only ever what it hid. The classic problem is at the base of the skull, where streaks between dense bones can obscure the adjacent brain — which is one reason MRI is preferred for looking at that region. A report mentioning it is telling the referring doctor which areas were less readable, and that is a statement about confidence rather than about disease.
What to do with it
For most scans nothing follows: the artefact is in a place that does not matter and the question is answered anyway. Where it obscured the area of interest, the answer is usually a different test rather than a repeat of the same one — MRI is unaffected by beam hardening, and modern scanners also have reconstruction techniques that reduce it. Radiologists are so used to the pattern that they recognise it as artefact rather than mistaking it for a finding.
Frequently asked questions
- Do the dark streaks mean something is wrong?
- No. They are an artefact of how X-rays pass through dense material, not a picture of anything in your body. Radiologists recognise the pattern immediately, which is why it is described as an artefact rather than reported as a finding.
- Why is it worst in my head?
- Because the skull base is where the densest bones sit closest together, so the beam passes through a lot of dense material at once. That is also why MRI is generally preferred when the question concerns structures in that region.
- Can it be avoided?
- It can be reduced but not eliminated. Modern scanners use reconstruction methods and dual-energy techniques that lessen it considerably. Where it still gets in the way, the practical answer is to use MRI instead, since it works on entirely different physics.
Picture problems, not body problems
Where this word comes up
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