Magnetic resonance imaging (MRI) uses a powerful magnetic field to create images of structures and organs within the body. It is a safe and noninvasive or minimally invasive test that can help physicians diagnose a wide range of diseases and conditions without subjecting the patient to radiation or radioactive isotopes.

An MRI works by placing the patient in a chamber surrounded by a magnetic field. The center (nucleus) of atoms in the patient’s body responds to the magnetic force in characteristic ways, allowing a computer to produce clear cross-sectional or three-dimensional images.

Because the MRI provides such clear images of the soft-tissue structures near and around the bones, it is the most sensitive test for examination of the body’s major joints, including the spine and the soft tissues of the limbs. MRI images can allow physicians to locate and identify the cause of pain, inflammation or bleeding in the tissues in and around the joints and bones. The images are so detailed that they allow physicians to see even the smallest tears and injuries to the ligaments and muscles as well as some fractures that x-rays cannot see.

MRI is widely used to diagnose sports injuries (e.g., fractures, tendinitis, ligament tear, knee meniscus injury), workplace disorders caused by repeated strain or use of force, and conditions such as carpal tunnel syndrome. MRI images can provide physicians with a clear picture of degenerative diseases such as arthritis, deterioration of joint surfaces, narrowing of the spinal canal (spinal stenosis) or a herniated disc. An MRI image of the brain can be part of a diagnosis of fibromyalgia.

Neurosurgeons often use MRI to evaluate a patient’s spinal cord following an acute injury or trauma. MRI is also useful for the detection and diagnosis of infections, such as septic arthritis or osteomyelitis (bone infection), and tumors involving the musculoskeletal system.

Other conditions revealed by MRI include:

• Eye or inner-ear tissue abnormalities
• Cardiac damage caused by heart attack, heart disease or conditions such as sarcoidosis
• Blood vessel plaques and blockages
• Functional disorders of organs, such as the lungs, liver, pancreas, kidneys and spleen
• Strokes and chronic disorders of the nervous system
• Brain abnormalities in patients with dementia
• Diseases of the pituitary gland
• Reproductive system and bladder problems
• Detection and staging of various forms of cancer

Sometimes MRI involves injection of a contrast medium (dye) into a vein that increases the clarity of the images by making the body’s tissues more responsive to the machine’s magnetic and radio waves. MRI is painless other than the brief discomfort of an injection and possible mild cramping from holding the body in position.