How does an MRI scan work?

The magnetic field temporarily aligns hydrogen particles in your body. Radio waves then disturb that alignment, and the particles release signals as they return to their usual state. A computer converts those signals into cross-sectional images that can be viewed from different angles. The scanner does not use ionising radiation. A [MRI Scanner](/technology/mri-scanner/) is noisy, so you may hear knocking or tapping while lying still inside the opening. Some examinations use contrast material injected into a vein to make selected tissues easier to distinguish.

MRI can help assess the brain, spine, joints, organs and soft tissues. It may be used alongside other tests when a clinician is investigating a finding such as a [Brain Tumour](/conditions/brain-tumour/) or deciding whether a [Biopsy](/treatments/diagnostics-and-staging/biopsy/) is needed.

Tell the imaging team if you have a pacemaker, implanted device, metal fragments, a history of kidney problems, or a possibility of pregnancy. Remove jewellery, watches, cards and other metal objects before entering the scan room. Follow any instructions about eating, drinking or medicines, especially if contrast is planned. During the scan, use the call button if you feel distressed; staff can communicate with you and may pause the examination.

Contact the imaging service promptly if you develop a rash, swelling, breathing difficulty or severe dizziness after contrast. Seek urgent help for trouble breathing, fainting or rapidly worsening swelling. After the scan, ask the referring clinician when and how the findings will be explained; an MRI image alone does not establish a cancer diagnosis.

Ask what body area will be scanned, whether contrast is recommended, how long you should expect to lie still, and when results will be available. You can also ask how the MRI fits with a [PSA Test](/treatments/cancer-screening/psa-test/) or other planned assessment.