Brain MRI scan: why it is done, what happens and how long results take

Magnetic resonance imaging, or MRI, is a way of taking detailed pictures of the inside of the body. According to NHS inform, the scanner is a large tube containing powerful magnets. You lie on a flat, motorised bed that moves into the tube, and radio waves are used while the images are taken. Because it does not use X-rays, it is a different kind of test from a CT scan, which is another scan sometimes used to look at the head.

The NHS describes an MRI scan as a test that helps diagnose conditions, plan treatment and check how well treatment is working. A brain MRI is simply that scan directed at the head. It shows the soft tissues of the brain in fine detail, which is why doctors choose it when they want a close look at the brain itself.

The scan is carried out in hospital by a radiographer, who controls the scanner from another room. A radiologist, a doctor trained to interpret scans, then studies the pictures and writes a report. You will not usually be told what the images show during the appointment.

There is no single reason for a brain MRI. NHS guidance on individual conditions mentions the scan in several different settings, and in each case it is one step in a wider assessment rather than a stand-alone answer.

• Suspected multiple sclerosis: the NHS lists an MRI scan among the tests used to see whether there is damage to the nerves in the brain or spinal cord.

• Memory problems and suspected dementia: the NHS says a brain scan, such as a CT scan or an MRI scan, might be one of the tests used when diagnosing dementia.

• Symptoms that might point to a brain tumour: the NHS says that if a GP cannot find a more likely cause, they may refer you to a neurologist for further assessment and tests, such as a brain scan.

• Other neurological symptoms: persistent or unexplained symptoms affecting the brain or nervous system may lead a specialist to request imaging as part of the work-up.

The hospital will tell you if you need to do anything beforehand. The NHS says you may be asked not to wear anything with metal in it, such as jewellery, hair clips or hearing aids, to remove coins and keys from your pockets, to change into a hospital gown if your clothes have metal parts, and not to wear make-up. NHS inform adds that watches, piercings, dentures, wigs that contain traces of metal and medicine patches should also come off, and that you can usually store valuables in a locker.

On the day, NHS inform says you should normally be able to eat, drink and take your medication as usual unless you have been told otherwise. In some cases people are asked not to eat or drink for up to 4 hours before the scan, depending on the area being scanned.

You will be asked to complete a safety questionnaire. The NHS says it asks whether you are or may be pregnant, are breastfeeding, have had surgery, have kidney problems, have metal parts in your body such as surgical clips, a pacemaker or dental work, or have allergies, including to contrast dye. Answer it carefully: it exists so the team can decide whether the scan is safe and whether any settings need to change.

NHS inform describes MRI as very safe and says most people can have it, but the magnet means metal needs to be checked first. Having metal in your body does not automatically rule the scan out. The medical staff can decide case by case whether there is a risk and whether extra measures are needed, and NHS inform notes that it may be possible to make a scan safe for a pacemaker or defibrillator when certain conditions are met.

Items it asks you to mention include pacemakers and implantable defibrillators, metal plates, wires, screws or rods used after fractures, nerve stimulators, cochlear implants, drug pump implants, brain aneurysm clips, prosthetic metal heart valves, metallic fragments in or near the eyes (a particular risk for people who weld or do metalwork), artificial joints, dental fillings and bridges, surgical clips, tattoos and permanent make-up, and insulin pumps or glucose monitors. If you are unsure about metal fragments, you may need an X-ray first.

On pregnancy, NHS inform says there is no evidence that MRI poses a risk, but your clinical team reviews each case to decide whether a scan is right, and contrast dye is only given if a radiologist decides it is appropriate. Tell the person referring you if you are or might be pregnant so this can be checked before you arrive.

You lie flat on the bed. For a head scan, NHS inform says a frame may be placed over the part being scanned, which holds receivers that help produce a clearer image. You are given earplugs or headphones because the scanner makes loud bangs and clicks, which NHS inform says patients have compared with standing next to roadworks. You can usually listen to music through the headphones.

The radiographer can hear you and speak to you throughout, and can see you through a viewing window and monitor. You are given a squeeze alarm so you can alert them if you have concerns. The most important thing you can do is lie still, because movement blurs the pictures. You may be asked to hold your breath briefly during some sequences.

If you dislike enclosed spaces, tell the team in advance. The NHS says you can talk to a healthcare professional beforehand if you are anxious or claustrophobic, you may be able to have a medicine to relax, and you can ask whether someone can accompany you. NHS inform adds that going in feet first can be easier for some people, although this is not always possible, and that you should raise any claustrophobia with the radiographer before starting.

Some scans include contrast dye by injection. The NHS says this makes more detail show up in the pictures. It also says that if you have contrast you may be asked to wait in hospital for up to 30 minutes afterwards so that staff can check for a reaction.

The NHS calls MRI a common procedure in which serious complications are rare. NHS inform describes it as painless and says no evidence has been found that the magnetic fields and radio waves pose a risk. Some people notice a tingling sensation or feel warm in the scanner, which passes quickly.

Contrast medium has its own possible effects. The NHS lists a small bruise where the injection went in, and side effects that may include feeling or being sick, a skin rash, a headache, a metallic taste and dizziness. Allergic reactions are described as rare and can include coughing, wheezing or sneezing, fainting, difficulty breathing or swallowing, or a rash with hives or itchy red skin. Most reactions happen soon after or within the first hour. Tell the radiographer straight away if you feel unwell during or after the scan.

NHS inform also notes that contrast agents can, in people with severe kidney disease, cause tissue and organ damage, which is why a blood test of kidney function may be arranged first. Let staff know if you have a history of allergic reactions or any blood clotting problems.

If you have a sedative, the NHS says someone needs to collect you and take you home by car or taxi, and you should not drive for 24 hours. NHS inform adds that you should not operate heavy machinery or drink alcohol for 24 hours after a sedative, and that a friend or relative should stay with you for the first day.

Staying still is difficult for babies and young children. NHS inform says they may be given a general anaesthetic before an MRI scan for that reason. If a child needs a scan, the referring team will explain what is planned.

Without sedation you can usually carry on as normal straight away. The NHS says you can eat and drink as usual after the scan, and NHS inform notes that an MRI is normally an outpatient procedure, so you do not stay overnight.

The radiologist writes a report for the doctor who arranged the scan, and that doctor discusses the findings with you. The NHS says it usually takes 1 to 2 weeks, and that you may need a follow-up appointment to talk it through. NHS inform notes waiting times depend on the hospital and that some scans are discussed with other specialists first.

If you have not heard anything after a few weeks, the NHS advises contacting the doctor who referred you. It is reasonable to ask what the result means for you, what happens next and what any unfamiliar terms mean.

A scan result is only one piece of the picture. A normal brain MRI does not always explain every symptom, and an abnormal-looking area is interpreted alongside your history and examination. That is why the conversation with the requesting doctor matters more than the report wording on its own.

On the NHS, a brain MRI is requested by a GP or hospital specialist when it is clinically indicated, and the report goes back to that clinician. Private imaging centres also offer MRI, and some people choose that route to avoid waiting. The scan itself, the safety questions and the radiologist report are broadly the same; what differs is the waiting time and who receives the report.

If you pay for a scan without a referral, make sure you know who will explain the result and arrange any follow-up, because a report alone can raise more questions than it answers. Your GP can help interpret a private report and decide whether further investigation is needed.