A brain MRI takes detailed pictures of the structure of your brain using a strong magnetic field and radio waves, not X-rays. It is good at showing things like multiple sclerosis lesions, tumours, old strokes, bleeds and structural causes of seizures. It cannot see thoughts, mood, pain or how well the brain is working moment to moment.
That is why a normal MRI does not rule out migraine, epilepsy, functional neurological disorder (FND) or a mental health condition. These are diagnosed mainly from your history and examination. The opposite surprise is also common. Scans of healthy people often show something unexpected, most of it harmless. On the day, a brain MRI usually takes between 15 minutes and an hour. Results usually take one to two weeks.
According to the US Food and Drug Administration (FDA), MRI gives better soft-tissue contrast than CT. CT is usually better for bone. MRI also uses no ionising radiation.
That makes MRI the scan of choice for many brain questions. Doctors use it to:
MRI is not always the first scan. For a sudden, severe "thunderclap" headache, NICE recommends an urgent non-contrast CT head scan first (NICE NG228).
An MRI shows structure. Many neurological and mental health conditions change how the brain works without changing how it looks.
Migraine and other common headaches. These are diagnosed from the pattern of symptoms. NICE tells doctors not to send people with migraine and other common headache types for neuroimaging "solely for reassurance" (NICE CG150). Our guide to telling migraine, tension and cluster headaches apart explains how the patterns differ.
Epilepsy. In the evidence NICE reviewed, no imaging test was accurate enough to diagnose epilepsy on its own. Imaging is used to look for a cause (NICE NG217). NICE does not routinely recommend MRI in idiopathic generalised epilepsy, which is not linked to structural brain abnormalities. So a normal scan is common and expected in many people with epilepsy.
Functional neurological disorder. NHS inform says scans in FND show no damage to explain the symptoms. It says FND should be diagnosed from its typical clinical features. It should not be diagnosed just because other tests are normal.
Dementia. NICE says Alzheimer's disease should not be ruled out based solely on a CT or MRI scan (NICE NG97). Our guide to memory worries and normal ageing covers what usually comes first.
Mental health and neurodevelopmental conditions. The NHS says there are no physical tests for depression. For autism in adults, NICE says neuroimaging should not be used routinely for diagnosis (NICE CG142).
A normal MRI is still useful. It can rule out some serious causes. But it is one piece of evidence, not the verdict.
An incidental finding is something the scan picks up that has nothing to do with why it was done. People sometimes call these "incidentalomas".
They are common. In the Rotterdam Study, 2,000 people aged 45 to 96 from the general population had research brain MRIs (Vernooij et al., NEJM 2007). Their average age was 63. The researchers found:
Silent infarcts and meningiomas became more common with age. Aneurysms did not.
A 2009 meta-analysis pooled studies of people without neurological symptoms (Morris et al., BMJ 2009). Across 16 studies and 19,559 people, 0.70% had an incidental tumour-type finding. Across 15 studies, 2.0% had other incidental findings, not counting white matter changes, silent infarcts or microbleeds. Higher-resolution scans found more. On average, 37 symptom-free people needed scanning to find one incidental brain finding.
Those authors concluded that the findings were not enough to justify screening healthy people with brain MRI. Most incidental findings never cause harm. Some lead to follow-up scans, worry or referrals. That trade-off is worth knowing about before any scan.
White matter hyperintensities are small bright spots on certain MRI sequences. Reports may also call them white matter lesions or white matter changes. They are often linked to ageing of the small blood vessels deep in the brain.
They are extremely common with age. Among 1,077 Rotterdam residents aged 60 to 90, only 5% had no white matter lesions (de Leeuw et al., JNNP 2001). The proportion with lesions rose with age.
They are not always meaningless, though. A meta-analysis of long-term studies linked them with higher risk of stroke (hazard ratio 3.3), dementia (1.9) and death (2.0) (Debette and Markus, BMJ 2010). These are associations from observational studies, not proof that the spots cause those outcomes. The authors said finding them should prompt a check of stroke and dementia risk factors.
Blood pressure is the big one. Our article on blood pressure and the brain explains how small-vessel damage builds up. The same process underlies much vascular dementia.
White matter spots also turn up more often in some people with migraine. In a 2013 meta-analysis, migraine with aura was linked to more white matter abnormalities (odds ratio 1.68) (Bashir et al., Neurology 2013). For migraine without aura, the link did not reach statistical significance.
What a finding means for you depends on your age, symptoms and other health. That is a conversation for the doctor who ordered the scan.
Some MRI scans use an injection of contrast medium, or dye, to show more detail. For MRI this is usually a gadolinium-based agent. The NHS says side effects are usually mild and short-lived. They include feeling sick, a rash, a headache, a metallic taste or dizziness. Allergic reactions are rare. You may be asked to wait for about 30 minutes afterwards.
Gadolinium can stay in the body for a long time. The US label for one agent, gadobutrol, says it is retained "for months or years" in brain, bone and other organs (DailyMed, Gadavist label). In 2017 the European Medicines Agency found no evidence that this brain deposition had harmed patients. As a precaution, it suspended or restricted some older "linear" agents in the EU. More stable "macrocyclic" agents remain in use at the lowest effective dose.
Kidney function matters. The same US label warns of a rare condition called nephrogenic systemic fibrosis in people with severe kidney disease or acute kidney injury. That is one reason the safety form asks about kidney problems.
MRI is safe for most people, but the magnet is always on. The FDA explains that it can pull on magnetic objects. The scanner's energy can heat some implants and cause burns. It can also stop electronic devices working properly.
So before the scan, you will fill in a safety form. The NHS lists questions about:
The FDA says people with implants should only be scanned if the device is confirmed "MR Safe" or "MR Conditional". An MR Conditional device is safe only under specific scanner conditions. A device with unknown status should be treated as unsafe. Bring your implant card or details if you have them.
If MRI is not possible, there are alternatives. NICE notes that severe claustrophobia, or a pacemaker that is not MRI-conditional, may mean a CT scan instead (NICE NG217).
The NHS describes the process:
You can eat and drink normally afterwards.
You are not alone, and few people end up unable to finish. Across one UK multi-centre service, 0.76% of scans were left incomplete because of claustrophobia between 2019 and 2021 (Hudson et al., Radiography 2022). Head scans and going into the scanner head first were linked to higher odds.
Tell the hospital before your appointment. The NHS says you may be offered a medicine to help you relax. You can also ask to bring someone for support. If you take a sedative, you should not drive for 24 hours, so arrange a lift. The FDA says an open scanner may suit some people, but not every scan can be done on one.
A radiologist reads the images and writes to the doctor who referred you. The NHS says this usually takes one to two weeks. The radiographer on the day usually cannot tell you the result. If you have heard nothing after a few weeks, contact the referring doctor.
Reports are written for doctors, so wording can sound alarming. Ask your doctor to explain any finding and what, if anything, happens next.
In Ireland. Most brain MRIs are arranged by a hospital specialist. GPs can also refer adults aged 16 and over for an MRI brain directly. This is the HSE's GP Access to Community Diagnostics scheme, which uses private providers. The Department of Health says the scheme is at no cost to the patient (as of January 2024, checked November 2026). Not every scan type is covered, so your GP will check.
In the UK. NHS brain MRIs are arranged through your GP or a specialist. For people diagnosed with epilepsy, NICE recommends MRI within six weeks of referral.
In the US. A doctor orders the scan. The FDA regulates MRI scanners and contrast agents.
Get help urgently if you have a sudden, very painful headache unlike anything before. The same applies to weakness in an arm or one side of the face, or slurred speech. The HSE says to call 112 or 999 in Ireland. In the UK call 999, and in the US call 911. Do not wait for a scan appointment. The signs of stroke are covered in our FAST guide.
No. These are diagnosed through clinical assessment. NICE says neuroimaging should not be used routinely to diagnose autism in adults. The NHS says there are no physical tests for depression.
That is a decision to discuss with your GP. A large review found incidental findings in symptom-free people were not enough to justify screening healthy people. Unexpected findings can lead to more tests and worry.
They are very common with age, and often linked to small blood vessel changes. They are also linked to higher stroke and dementia risk in studies. Ask your doctor what they mean for you, and whether your blood pressure and other risk factors need checking.
For most people, side effects are mild and short-lived. Serious allergic reactions are rare. Tell staff about kidney problems, allergies, pregnancy or breastfeeding. Gadolinium can stay in the body for years, though EU regulators found no evidence that brain deposits had caused harm.
An MRI shows structure, not function. Migraine, many types of epilepsy, FND and mental health conditions often have normal scans. A normal result can still help rule out other causes.
This article is general information, not medical advice. It does not replace advice from your GP, specialist or radiology team. Talk to them about your own scan and results.
Reviewed by: Proco Team
Last updated: November 2026