Magnetic resonance imaging (MRI) is very safe and most people are able to have the procedure.
But in some instances an MRI scan may not be recommended.
Before having an MRI scan, you should tell medical staff if:
you think you have any metal in your body
you're pregnant or breastfeeding
The strong magnets used during the scan can affect any metal implants or fragments in your body.
MRI scans aren't usually recommended for pregnant women.
Although they're thought to be generally safe to use in later pregnancy (after 3 months), it's not known whether the strong magnetic fields have any long-term effects on the developing baby.
Metal implants or fragments
Having something metallic in your body doesn't necessarily mean you can't have an MRI scan, but it's important for medical staff carrying out the scan to be aware of it.
They can decide on a case-by-case basis if there are any risks, or if further measures need to be taken to ensure the scan is as safe as possible.
For example, it may be possible to make a pacemaker or defibrillator MRI-safe, or to monitor your heart rhythm during the procedure.
You may need to have an X-ray if you're unsure about any metal fragments in your body.
Examples of metal implants or fragments include:
a pacemaker – a small electrical device used to control an irregular heartbeat