MRI

Magnetic resonance imaging (MRI) is a medical imaging technique used to visualize detailed internal structures. It uses strong magnetic fields and radiofrequency pulses to excite hydrogen nuclei in the body's water and fat. When the radiofrequency field is removed, nuclei return to alignment and emit signals that are detected and transformed into images.

Unlike imaging methods that rely on ionizing radiation, MRI does not use X-rays. Image contrast arises from the properties of tissue, notably T1 and T2 relaxation times and proton density. Different pulse sequences create varying contrasts, with common examples including T1-weighted, T2-weighted, diffusion-weighted, and functional sequences. In some studies, gadolinium-based contrast agents are used to enhance tissue visibility.

During an MRI scan, the patient lies inside a large bore magnet. Gradient coils spatially encode signals, while radiofrequency pulses and receivers generate and capture data. The resulting information is processed to form cross-sectional images that can be viewed in multiple planes. The technique is generally safe but can be limited by metal in or on the body, patient claustrophobia, and motion. Certain implants, devices, or foreign bodies may be contraindications.

Applications of MRI span neurology, musculoskeletal, cardiovascular, abdominal, and oncologic imaging. It offers excellent soft tissue contrast and can visualize the brain, spinal cord, joints, organs, and blood vessels. Advances include functional MRI, which assesses brain activity, and MR angiography, which images blood vessels without iodinated contrast.