Magnetic resonance imaging uses strong magnetic fields and radio waves to produce images of the inside of the body. While CT is often a better method for evaluating bones and blood vessels, MRI is frequently a better test for evaluating soft tissue, such as the brain, spinal cord, nerves, muscles, tendons, and breast tissue.
With brain, spinal cord, and peripheral nerve disorders, MRI has allowed healthcare providers to diagnose conditions that could only be assumed clinically in the past. For example, practitioners can now diagnose multiple sclerosis with an MRI, a diagnosis that was limited to an assessment of symptoms alone before MRI was available (and could only be confirmed on an autopsy).
For breast cancer screening, MRI is more accurate than mammography, but the higher price makes it impractical for people who do not have underlying risk factors for breast cancer. One form of MRI, called functional MRI, can even give an estimate of brain activity.
An advantage of MRI is that it does not use ionizing radiation, which has been linked to an increased risk of cancer, especially in children. Limitations include the cost and that it may not be used in people who have metal in their body.