Magnetic Resonance Imaging (MRI) and MS Diagnosis

Last updated June 27, 2022, by Marisa Wexler, MS

Fact-checked by Patricia Silva, PhD

Magnetic resonance imaging (MRI) is a noninvasive technique used to take detailed images of the body’s internal structures and tissues. MRI is the preferred imaging tool to assess damage in the brain and spinal cord that results from multiple sclerosis (MS) and it can aid in diagnosing the disease and tracking its progression.

How does MRI work?

Unlike an X-ray or a computed tomography (CT) scan, MRI does not rely on radiation. Instead, the technique uses very powerful magnetic fields to image water molecules in the body’s tissues.

A significant part of the human body is made up of water and each water molecule is composed of two hydrogen atoms attached to one oxygen atom (H2O).

Simplistically, MRI works by using powerful magnetic fields to temporarily alter the orientation of subatomic particles (protons in hydrogen atoms) within water molecules inside the body. Then, radio waves are used to force these particles out of this orientation and return to their original alignment. As they realign, protons release resonance signals that are transmitted to a computer, which ultimately uses the signals to construct an image.

How is MRI used in MS?

MS is caused by the body’s immune system accidentally attacking the myelin sheath, a fatty coating around nerve fibers that helps them send electrical signals.

Because myelin is fatty and fats and water don’t mix, healthy myelin sheaths generally repel water. However, when the myelin sheath is damaged in MS, there is less fat — and consequently, more water accumulates in that area. These water-rich areas of damage, called lesions, are visible on MRI as spots that are markedly brighter or darker (depending on the type of scan) than the surrounding area.

Diagnosing MS

In order to receive a formal MS diagnosis, a person must show evidence of MS-like damage that affects more than one region of the nervous system, and that occurs at more than one point in time — hence the “multiple” in “multiple sclerosis.” MRI is the gold standard for identifying and monitoring this damage in the brain and spinal cord.

A person who experiences a first attack of MS-like symptoms and brain inflammation — as detected via MRI — is said to have clinically isolated syndrome (CIS). MRI can be used to monitor CIS patients for the development of additional inflammatory damage, even if the person experiences no new symptoms, which may help facilitate a faster MS diagnosis.

Sometimes, a person who undergoes MRI for other health reasons is found to have MS-like lesions in their brain or spine, even though they don’t have any overt MS symptoms. This is referred to as radiologically isolated syndrome, or RIS. Some people with RIS will go on to develop MS, but others will not. MRI may be used to check for further inflammatory brain damage in people with RIS to aid in defining the diagnosis.

Measuring disease progression

Once a person is diagnosed with MS, regular MRI scans help in tracking the disease’s progression, which can aid in making treatment decisions such as whether to continue with a current therapy or change to a new one.

Follow-up MRIs are generally recommended every six months to two years. Where possible, follow-up scans should be obtained on the same scanner, so that it’s easier to make comparisons from one scan to the next.

In addition to tracking the development of new lesions, MRIs are also used to assess brain atrophy — the gradual loss in brain volume over time. In MS patients, brain atrophy can occur at rates higher than 1% per year, far exceeding the normal rate. Assessing brain atrophy can be used to predict an individual’s risk of future physical and cognitive disability, and to inform decisions about treatment and care.

What are the different kinds of MRI?

There are a number of different types of MRI scans that can be useful for detecting specific types of lesions. The most commonly used in clinical practice include:

  • T1-weighted scan, with or without gadolinium
  • T2-weighted scan
  • T2-weighted fluid attenuated inversion recovery (FLAIR) sequence

Active and inactive lesions can be distinguished on MRI using a technique called gadolinium enhancement. Just before the scan, a contrast agent called gadolinium is injected into the patient’s bloodstream. Normally, a protective wall called the blood-brain barrier stops any of the contrast agent from entering the brain and spinal cord, so no contrast agent is visible. However, active inflammation in a lesion causes this barrier to grow “leaky,” resulting in a bright spot at that lesion as the contrast agent leaks past the barrier. These areas of active inflammation can be referred to as “enhancing lesions.”

Inactive, older lesions will not be detected by this technique with gadolinium.

The terms T1 and T2 refer to the time between the magnetic pulses and when the image is taken. Active gadolinium-enhancing lesions usually are imaged specifically via T1-weighted scan, while T2-weighted scan is generally used to image the overall lesion load, both old (inactive) and new (active) lesions.

A T1-weighted scan without gadolinium can reveal persistent lesions, which can show up as dark areas (“black holes” or hypointense lesions) that are thought to indicate areas where permanent nerve damage occurred.

T2-weighted FLAIR is a technique to improve the detection of lesions by suppressing signals (or interference) from the cerebrospinal fluid (CSF) — the liquid that surrounds the brain and spinal cord.


MRI scanners rely on powerful magnets. Generally, the more powerful the magnet, the better the resolution of the image produced by the MRI scan.

The strength of MRI magnets is measured by a unit called Tesla (T). One Tesla is equal to roughly 20,000 times the strength of the Earth’s magnetic field at its surface. Most MRI scanners used in clinics have magnets of 1.5 or 3 T, though more powerful magnets — 7 T, or even more than 10 T — are being explored in research.

Is MRI safe?

MRI is generally considered a very safe procedure. The scan itself is not painful. Some people may feel claustrophobic during MRI scans; anti-anxiety medications can help if this is a problem.

Because the MRI uses powerful magnets, it can affect metal that is in or on the body. To ensure safety, it’s important to remove any worn metal (jewelry, eyeglasses, etc.) before a scan. People with certain metal implants should not undergo a MRI scan — clinicians typically will perform a detailed screening procedure to identify if an individual has any implants or other conditions that might raise safety issues during an MRI.

Contrast agent safety

Gadolinium-based contrast agents, sometimes called GBCAs, are injected into the body prior to some MRI scans in order to help detect areas of active inflammation. These agents are generally considered safe.

In rare cases — specifically in people with impaired kidney or liver function — GBCAs can increase the risk of nephrogenic systemic fibrosis (NSF), a serious condition marked by fibrosis (scarring) throughout the body. Recent research has shown that GBCAs can be retained in deposits in the brain and other body tissues; these deposits have not been linked to any overt health problems, but their clinical relevance is not completely understood.

Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

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