MRIs

Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique that visualizes internal structures with high soft tissue contrast. It uses a strong static magnetic field, gradient fields, and radiofrequency pulses to excite hydrogen protons in body tissues. When protons relax, they emit signals that are spatially encoded to form cross-sectional images. Unlike X-ray and CT, MRI does not use ionizing radiation, making it a preferred modality for many neurologic and musculoskeletal assessments. Scans are performed in a bore-like magnet; patients must remain still, and sessions range from 15 to 60 minutes or longer depending on protocols.

MRI sequences emphasize different properties; common ones include T1- and T2-weighted imaging, diffusion-weighted imaging, and, in functional MRI, blood-oxygen-level-dependent contrasts. Gadolinium-based contrast agents may be used to enhance lesions, but carry small risks; in severe kidney impairment, gadolinium can cause nephrogenic systemic fibrosis. Safer agents have reduced risk, yet contrast is not always required. Contraindications include non-MRI-compatible implants, certain electronic devices, and severe claustrophobia. Safety measures include ear protection, screening for metal, and monitoring for adverse reactions.

Limitations include longer exam times, sensitivity to motion, higher cost, and limited availability in some settings. MRI is often complementary or superior to CT and ultrasound for soft tissue evaluation and is central to brain and spinal imaging, joint and musculoskeletal assessment, and cardiac and abdominal studies with specialized protocols. The field dates to the 1970s, building on work by researchers such as Lauterbur and Mansfield.