CT scanner and MRI: what happens during each test

Both require you to lie on a moving table, but the equipment and examination experience differ. The prescribed machine is chosen for the anatomical detail your care team needs.

A CT unit has a short, doughnut-shaped opening. The table moves through it while internal components rotate; you may be asked to hold your breath briefly so movement does not blur an image.

An MRI unit usually places the examined area within a longer tunnel. It produces loud tapping and knocking sounds, so hearing protection is provided. You remain in contact with the radiographer and receive a call device.

Remove items as directed and follow clothing instructions. MRI screening is especially detailed because loose metal can move toward the magnet and some devices work only under specified scanning conditions.

Tell staff about pacemakers, pumps, clips, hearing implants, metal fragments, previous operations, kidney disease, pregnancy or possible pregnancy, and prior contrast reactions. If enclosed spaces are difficult, contact the department early so suitable support can be planned.

Alert the radiographer straight away if positioning causes severe pain, you feel intense heat, you cannot breathe comfortably, or an injection site becomes painful. Do not try to climb off the moving table without assistance.

If contrast was given, emergency symptoms include facial or throat swelling, breathing difficulty, collapse, or a fast-spreading rash. Worsening swelling, numbness, colour change, or blistering at the cannula site also needs prompt clinical review.

Ask how long your particular examination is expected to take, which body part must remain still, and whether contrast is planned. If pain limits your position or anxiety may prevent completion, discuss this before the appointment rather than waiting until the scan begins.