The long-term risks of medical imaging

When it comes to the long-term risks of imaging, it helps to separate the scans that use radiation from those that don’t.

Only some scans carry a radiation risk

Ultrasound and MRI use no ionising radiation, so they carry no radiation-related long-term risk.^[2] The discussion of long-term risk applies only to scans that do use radiation — X-ray, CT and nuclear medicine.

A small, theoretical cancer risk

For those scans, the only recognised long-term concern is a very small possible increase in lifetime cancer risk from the radiation dose.^[2] Two points keep this in perspective:

• At the low doses used in most imaging, this increase has not been clearly demonstrated — it’s hard to detect against the roughly 1-in-2 lifetime cancer risk we all carry anyway.
• The risk is estimated cautiously, by extrapolating down from situations involving much higher doses (such as atomic-bomb survivors). This deliberately errs on the side of safety.^[2]

Higher-dose studies (like CT) carry a larger estimated risk than a simple X-ray, which is why they’re justified more carefully.^[1]

Benefit almost always wins

For any single, genuinely needed scan, the benefit — a correct diagnosis, the right treatment, avoiding something worse — almost always outweighs the small theoretical risk.^[1] The risk matters most across populations and repeated scans, which is why imaging is used thoughtfully rather than routinely.

Frequently asked questions

Will a scan give me cancer?

For a single needed scan the risk is very small and theoretical — at low doses it hasn’t been clearly shown, and the benefit almost always outweighs it. Ultrasound and MRI carry no such risk.^[2]

Why is the risk described as “theoretical”?

Because at the low doses used in imaging, an increase in cancer hasn’t been clearly measured. The risk is estimated cautiously from higher-dose exposures, erring on the side of safety.^[2]

Are non-radiation scans completely risk-free?

They carry no radiation risk. Ultrasound and MRI have excellent safety records; MRI has its own precautions (metal, the magnet) but no ionising-radiation risk.^[2]