MRI of the lumbar spine: what it shows, how it works and what to expect

An MRI scan takes detailed pictures of the inside of your body. The NHS says it is used to help diagnose conditions, plan treatment and check how well treatment is working. A lumbar spine MRI focuses on the lower back: the lumbar vertebrae, the discs between them, the spinal canal and the nerves that leave it.

The scanner is a short tunnel open at both ends. University Hospital Southampton explains that you lie on your back on a motorised bed and enter head first, that pads and supports are used for comfort, and that you must lie very still. A radiographer operates the scanner from another room, and you can talk to them through a built-in microphone.

Because MRI shows soft tissues well, it can show discs, nerve roots and the spinal canal. Torbay and South Devon says MRI is mainly used to confirm a clinical diagnosis such as pain arising from a nerve root, and that once a level is identified that corresponds to your symptoms, this can help to guide treatment. It can also help to eliminate causes of back pain such as infection and tumours, although these are rare.

The scan is interpreted together with your symptoms and examination rather than in isolation, which is why the same report can lead to different advice for different people.

Many people expect an MRI for back pain, but the NHS says low back pain often improves on its own within a few weeks, and that very rarely back pain can be a sign of a serious problem such as a broken bone, cancer or an infection. Torbay and South Devon says MRIs are not normally used to determine causes of low back pain, and that X-rays and CT scans are not routinely used either, being primarily used in trauma or complex surgical planning.

The NHS says to see a GP if back pain does not improve after treating it at home for a few weeks or is stopping you doing your day-to-day activities, and lists signs that need urgent assessment, below. Whether a scan is needed is a clinical decision.

You will be sent a safety questionnaire to complete and bring with you. University Hospital Southampton says you will change into a hospital gown and put belongings in a locker, and you must remove jewellery, piercings, drug patches, metallic denture plates and hearing aids. The NHS says you may be asked not to wear make-up and to remove coins or keys, and will be asked about pregnancy, breastfeeding, previous surgery, kidney problems, metal parts and allergies.

You must contact the department in advance if you have a cardiac pacemaker or defibrillator, a heart valve replacement, have had surgery on your head, metal in your eyes from welding, any metallic or electronic implants, any surgery within the past six weeks, auditory implants such as cochlear implants, or have ever swallowed a capsule camera. The factsheet says that if you do not let the department know, the scan may have to be postponed.

If you feel anxious or have a fear of small spaces, the NHS advises talking to a healthcare professional before the appointment. You may be able to have a medicine to help you relax, and you can ask to bring someone to support you.

The scanner makes loud tapping noises, as the electric current in the coils is switched on and off, and you will be given ear plugs and the option to listen to music through headphones. You may feel your body temperature increase and tingling in your hands and feet, which University Hospital Southampton says are normal sensations, and you will be given an emergency buzzer.

Sometimes a contrast medium (dye) is injected to show more detail. The NHS says that if you receive contrast you may be asked to wait in hospital for up to 30 minutes in case of a reaction. Side effects such as feeling sick, a rash, a headache or a metallic taste are usually mild, and allergic reactions are rare.

The images need to be looked at by a radiologist, who writes to the doctor who referred you. The NHS says this usually takes 1 to 2 weeks and that you may need a follow-up appointment. If you have not heard anything after a few weeks, contact the doctor who referred you.

The NHS advises telling your doctor if you have questions or do not understand your results. Ask which findings are relevant to your symptoms and what the result means for treatment.

The NHS says to call 999 or go to A&E if you have back pain and pain, tingling, weakness or numbness in both legs, loss of feeling around your genitals or anus, changes in your bladder or bowels such as difficulty peeing or peeing or pooing yourself, changes in how your penis or vagina feels during sex, chest pain, or if it started after a serious accident. Ask for an urgent GP appointment or contact NHS 111 if you feel hot, cold, shivery or generally unwell, or if severe pain starts suddenly or is getting worse quickly.

These symptoms need clinical assessment rather than waiting for a routine scan appointment.