What should you know about how an MRI scanner works?

The scanner's magnet aligns hydrogen particles found naturally in the body. Radiofrequency pulses briefly change that alignment. As the particles return toward their usual state, they release signals. Coils placed around the body area receive those signals, and a computer uses their timing and strength to calculate images in slices.

The machine may make loud knocking or tapping sounds as its gradient coils switch during image collection. The table can move through the magnet more than once because different sequences answer different questions. The images show anatomy and tissue characteristics; a radiologist interprets them and sends a report to the requesting clinician.

Remove metal items and answer the safety questionnaire carefully. Tell staff about implants, metal fragments, medication patches, pregnancy, kidney problems and anxiety in enclosed spaces. Follow instructions about contrast or eating and drinking. Keep the body part still and use the call system if you need attention. Ear protection is commonly provided because the scanner is noisy.

The [MRI Scanner](/technology/mri-scanner/) overview describes the main equipment. You can also read the patient-focused [MRI Scan](/treatments/diagnostics-and-staging/mri-scan/) guide and the focused [Breast MRI](/treatments/diagnostics-and-imaging/breast-mri/) page.

Tell the team immediately if you feel heat, pain, pulling, breathing difficulty or severe anxiety during the scan. Outside the imaging appointment, urgent assessment is needed for sudden weakness, new confusion, a seizure, severe sudden headache, chest pain or severe breathing difficulty. Do not wait for a planned scan when an emergency symptom is present.

What part of my body will be scanned, and what will the images help clarify? Will contrast or special preparation be needed? How long should I expect to remain still? Who will discuss the report with me?