Imaging study · No radiation

MRI scan

Also known as: magnetic resonance imaging, MR scan, MR angiography, functional MRI, cardiac MRI

Magnetic resonance imaging uses a strong magnet and radio waves, not radiation, to produce detailed pictures of soft tissue: the brain, spinal cord, joints, muscles and organs.

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How it works

A powerful magnet aligns the hydrogen nuclei in the body's water and fat. Radio pulses knock them out of alignment and, as they relax back, they emit faint signals that differ by tissue type. Different pulse sequences (T1, T2, diffusion, fat suppression) emphasise different properties, giving unrivalled soft-tissue contrast without ionising radiation.

What it shows

  • Brain and spinal cord: stroke within minutes (diffusion), multiple sclerosis, tumours, epilepsy foci, dementia patterns
  • Spine: disc herniation, nerve compression, infection, cord injury
  • Joints: cartilage, menisci, ligaments, tendons, bone marrow oedema (early stress fractures)
  • Heart: muscle scar, cardiomyopathy, congenital disease
  • Liver, pancreas, bile ducts (MRCP), prostate, pelvis, breast

Best for

  • Any question about the brain, spinal cord or nerves
  • Ligament, cartilage and tendon injuries of the knee, shoulder and ankle
  • Characterising liver, pancreatic and prostate lesions
  • Children and pregnancy, where radiation is avoided

Not the right tool for

  • Emergencies needing speed (a scan takes 20-60 minutes and the environment is hard to monitor)
  • Lungs and calcified structures (few hydrogen nuclei; CT is better)
  • People with certain implants, severe claustrophobia, or who cannot lie still

What to expect

Modality
MRI (magnetic resonance imaging)
Preparation
A detailed safety questionnaire about implants, metal fragments, pacemakers and previous surgery; all metal removed; ear protection for the loud knocking. Fasting for some abdominal scans.
Duration
20-60 minutes lying still inside a tube; each sequence lasts a few minutes.
Radiation
No ionising radiation; the magnetic field and radio waves have no known lasting effect at diagnostic strengths.
Contrast
Gadolinium, injected into a vein, highlights tumours, inflammation and blood vessels; rare allergic reactions.
Risks
Ferromagnetic objects become projectiles; older pacemakers, cochlear implants, aneurysm clips and metal in the eye can be dangerous. Gadolinium contrast is avoided in severe kidney disease and pregnancy. Claustrophobia is the commonest problem.

Common uses

RegionTypical question
BrainStroke, tumours, multiple sclerosis, epilepsy, dementia, headache with red flags
SpineSciatica with weakness, suspected cauda equina, infection, myelopathy
Knee and shoulderLigament and meniscal tears, rotator cuff tears, cartilage
Abdomen and pelvisLiver lesions, bile duct stones (MRCP), prostate cancer, endometriosis, rectal cancer staging

Studies this page covers

Brain MRISpine MRICardiac MRIBreast MRIAbdominal MRIPelvic MRIMusculoskeletal MRIMR angiographyMR venographyMagnetic resonance cholangiopancreatographyFunctional MRIDiffusion MRIPerfusion MRIMR spectroscopyProstate MRI

Named studies of the master test taxonomy that this modality page covers; each links to its test category.