MRI Scanning

Magnetic resonance imaging (MRI) is the most detailed way of looking at the soft tissues of the spine — the discs, the spinal cord, the nerve roots, the ligaments and the fluid around them. Unlike X-rays and CT, it uses no ionising radiation. Instead it uses a strong magnet and radio waves to build up cross-sectional images that can be viewed as thin "slices" from any angle. For most spinal problems involving the nerves or cord — sciatica that is not settling, suspected nerve compression, and questions of infection, inflammation or tumour — MRI is the investigation of choice.

The body is mostly water, and water contains hydrogen. Inside the scanner's powerful magnetic field, these hydrogen atoms line up. A brief pulse of radio waves nudges them out of alignment, and as they settle back they release a faint signal that the scanner detects. Because different tissues — a healthy disc, a worn disc, nerve, fat, bone marrow, fluid — release this signal in slightly different ways, the computer can turn it into images with remarkable soft-tissue contrast. By changing the timing of the pulses (the "sequences"), radiologists can make the same anatomy look different in ways that highlight water, fat, swelling or bleeding.

You lie on a padded table that slides into a tube-shaped scanner. The magnet is always on, so before entering the room you will be asked detailed safety questions about any metal in your body — pacemakers, certain implants, surgical clips or metal fragments — because these can be affected by the field. The scan is painless, but it is noisy, producing loud knocking and buzzing sounds while the images are taken, so you will be given ear protection. Staying still is important, as movement blurs the pictures. A spinal MRI commonly takes somewhere in the region of twenty to forty-five minutes depending on how much is being examined. You can usually eat, drink and take your normal medication beforehand unless told otherwise.

MRI is the cornerstone of soft-tissue spinal imaging. It shows a slipped disc pressing on a nerve, narrowing of the spinal canal, changes within the cord itself, and early signs of infection, inflammation or tumour long before they appear on other tests — all without radiation. Its one important caveat is that it is very sensitive: age-related changes such as worn or bulging discs are extremely common in people with no pain at all, so an MRI is always interpreted alongside your symptoms and examination rather than on its own.

• —NICE — Low Back Pain and Sciatica in Over 16s (NG59)
• —Royal College of Radiologists — iRefer: Making the Best Use of Clinical Radiology
• —MHRA — Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use
• —British Association of Spine Surgeons (BASS)

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.