Article · Clinical
CT vs MRI: When to Use Each
CT (computed tomography) and MRI (magnetic resonance imaging) are the two main cross-sectional modalities. CT is fast, widely available and excellent for bone, lung and acute haemorrhage; MRI is slower, more expensive and superior for soft tissue, brain parenchyma, spine and musculoskeletal detail.
A clinician's cheat-sheet for choosing between CT and MRI.
Use CT for
Acute trauma, acute stroke (non-contrast first), suspected intracranial haemorrhage, pulmonary embolism (CTPA), acute abdomen, urolithiasis, lung nodules, fractures.
Use MRI for
Brain tumour, demyelination, dementia work-up, spine (disc, cord, nerve roots), musculoskeletal (ligaments, cartilage, marrow), pelvis (prostate, gynae), liver lesion characterisation, MR cholangiopancreatography, breast.
Contraindications and caveats
MRI: pacemakers and certain ferromagnetic implants, severe claustrophobia, very obese patients beyond bore limits. CT: ionising radiation (avoid in young pregnant patients when alternatives exist), iodinated contrast in severe renal impairment.
Quick facts
- CT: fast, bone/lung/haemorrhage
- MRI: slow, soft tissue/brain/spine/MSK
- Stroke: non-contrast CT first; MRI for confirmation