Magnetic resonance imaging is a medical imaging technique used in radiology to investigate the anatomy and physiology of the body in both health and disease. MRI scanners use strong magnetic fields and radio waves to form images of the body. The technique is widely used in hospitals for medical diagnosis, staging of disease and for follow-up without exposure to ionizing radiation. Since MRI does not use any ionizing radiation its use is recommended in preference to CT scan. Contraindications to MRI include most cochlear implants and cardiac pacemakers, shrapnel and metallic foreign bodies in the orbits. The safety of MRI during the first trimester of pregnancy is uncertain, but it may be preferable to alternative options.