Magnetic resonance imaging (MRI) is a non-invasive imaging method that uses radio waves and a powerful magnetic field rather than x-rays to produce clear and detailed images of virtually any part of the body. This procedure has greatly improved the ability to visualize normal and diseased tissue in the spine (also called the "vertebral column" or "backbone"), the bony structure that encloses the spinal cord. MRI frequently makes it possible to determine the cause of back pain. The examination shows the anatomy of the vertebrae that make up the spine, as well as the spinal cord and the spaces between the vertebrae through which nerves pass. MRI requires specialized equipment and expertise to perform it properly and to correctly interpret the findings.

Perhaps the most common reason for spinal MRI is to detect a bulging, degenerated or herniated intervertebral disk a frequent cause of severe lower back pain and sciatica.
Compressed (or pinched) and inflamed nerves are visible on MRI. In some cases the cause of nerve compression, whether from a herniated disk, arthritis or some other abnormality, also is demonstrated. MRI generally is the next non-invasive imaging examination used after x-rays of the lower spine; however, in cases of suspected disk herniation, MR may be the first study ordered.

MRI is frequently done to help plan surgeries on the spine such as the decompression of a pinched nerve or spinal fusion. MRI performed after spinal surgery will show whether anything has changed and whether post-operative scarring or infection is present. If a patient has failed to improve as expected, MRI may show why.

The exam can help to diagnose or rule out spinal infection or tumors that arise in, or have spread to, the spine; the common tumors include prostate, lung and breast cancers.
When done before steroids are injected to relieve spinal pain, MRI can ensure that the medication will not be mistakenly injected into a tumor or site of infection.
If your child has trouble with daytime wetting and does not fully empty the bladder, imaging the spinal cord may show why this is happening.

MRI generally is not done in the first 12 weeks of pregnancy; however, in urgent situations it may be performed. Radiologists prefer to use other methods such as ultrasound imaging in pregnant women unless no examination other than MRI will do. It may not be possible to perform MRI in a very obese patient, although an open unit will work in most cases. The presence of an implant or other metallic object often makes it difficult to obtain clear images, and patient movement can have the same effect. A patient with severe pain may not be able to lie still during imaging.

The MRI findings by themselves do not establish an absolute diagnosis, but in most situations the findings will suggest the correct diagnosis. The images must be interpreted along with the patient's history, physical findings and information from other tests. Vertebral fractures may be better detected by CT scanning. MRI may be more costly than other imaging methods, including CT scanning.