Magnetic resonance imaging (MRI) is a noninvasive technique used to take detailed images of the body’s internal structures and tissues. An MRI is the preferred imaging tool to assess damage in the brain and spinal cord that results from multiple sclerosis (MS). It also can aid in diagnosing the neurological disease and tracking its progression.
Unlike an X-ray or a computed tomography (CT) scan, an 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, MRIs work 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 them to their original alignment. As they realign, the protons release resonance signals that are transmitted to a computer, which ultimately uses the signals to construct an image.
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 don’t mix with water, 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 scans as spots that are markedly brighter or darker (depending on the type of scan) than the surrounding area.
To receive a formal MS diagnosis, a person must show evidence of MS-like damage that affects more than one region of the central nervous system, comprised of the brain and spinal cord, 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, so it is usually a key part of the diagnostic workup for people with suspected MS.
Such scans can be used to help detect MS and assess disease activity in all MS disease types — including relapsing-remitting MS, secondary progressive MS, and primary progressive MS. An MRI also may help to identify early stages of MS-like disease.
Once a person is diagnosed with MS, regular MRI scans help in tracking the disease’s progression, which can aid in making MS 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. If 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 used to assess brain atrophy — the gradual loss in brain volume over time. In MS patients, brain atrophy can occur at rates greater 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.
MS lesions are generally visible on MRI scans from the earliest stages of the disease, and they may even be apparent before a person experiences any MS symptoms.
An individual who experiences a first attack of MS-like symptoms and brain inflammation — as detected via MRI — is said to have clinically isolated syndrome, called CIS. MRI scans can be used to monitor CIS patients for the development of additional inflammatory damage, even if the person experiences no new symptoms. Thus, an MRI may help facilitate a faster MS diagnosis.
Sometimes, patients who undergo MRIs for other health reasons are 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 (RIS). Some people with RIS will go on to develop MS, but others will not. An MRI may be used to check for further inflammatory brain damage in people with RIS to aid in defining the diagnosis.
The key difference between a normal MRI scan and the scan of someone with MS is the presence of lesions in the brain. These lesions represent areas where inflammation has caused damage to the myelin sheath, and they are visible on MRI scans as spots of markedly altered color (usually bright or white spots, though on some types of scans, lesions instead appear darker than the surrounding matter).
Below is shown an abnormal brain MRI from a young person with MS. In this scan, several lesions are visible as bright white spots. On a brain scan of someone without MS, the brain would appear more uniformly gray, without such bright spots.
Properly interpreting MRI scans requires training and expertise, so patients should always discuss the results of MRI scans with a qualified medical professional.
Shown is an image from a brain MRI of a young multiple sclerosis patient. The white spots correspond to demyelinating lesions. (Credit: ISM/SOVEREIGN)
MS is defined by the presence of lesions — areas of inflammatory myelin loss, a process known as demyelination — that develop in several parts of the central nervous system at multiple points in time. To be diagnosed with MS, a person must show clear evidence of these lesions.
An MRI is the gold standard for detecting MS lesions, although some lesions do not show up on MRI scans — for example, some may be too small to be clearly seen through this technique. Symptoms that are indicative of a lesion in a particular part of the nervous system may be used as evidence for a lesion even if the MRI doesn’t show it. In such cases, however, it is critical to rule out other potential causes of the symptoms and MS mimics.
There are a number of different types of MRI scans that can be useful for detecting specific types of MS lesions. Those most commonly used in clinical practice include:
Active and inactive lesions can be distinguished on MRIs 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 this contrast agent from entering the brain and spinal cord, so no contrast agent is visible on the MRI scan. However, active inflammation in a lesion causes this barrier to become 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 a T1-weighted scan, while T2-weighted scans are 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. These “black holes” or hypointense lesions are thought to indicate areas where permanent nerve damage occurred.
The T2-weighted FLAIR is a technique used 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.
An 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 is important to remove any worn metal (jewelry, eyeglasses, etc.) before a scan. People with certain metal implants should not undergo an MRI scan — clinicians typically will perform a detailed screening procedure to identify whether an individual has any implants or other conditions that might raise safety issues during an MRI.
Gadolinium-based contrast agents, sometimes called GBCAs, can be 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.
The MRI itself usually lasts 15 to 90 minutes, depending on the specific type(s) of scan being used and which part(s) of the body may be imaged. Typically, multiple images are acquired. These images are interpreted by a radiologist, and the results are shared with the primary healthcare team and communicated to the patient. This process commonly takes a week or two, though turnaround times vary from clinic to clinic. It’s advised patients ask their healthcare providers when to expect results from MRI scans.
Contrast agents like gadolinium are typically used to detect areas of active multiple sclerosis (MS) driving inflammation on MRI scans. However, contrast agents are not needed for scans that detect any MS lesions (actively inflamed or not), so it is possible to diagnose MS without the use of these agents. It is generally recommended that, when feasible, patients should undergo scans both with and without contrast. This will help to facilitate an MS diagnosis, or not, as quickly as possible.
MRI scans of the cervical or lumbar spine — the neck and lower regions of the spinal cord, respectively — may be useful for detecting multiple sclerosis (MS) lesions in those regions. To receive a formal diagnosis of MS, a person must show evidence of lesions in at least two of four parts of the central nervous system, which include three brain regions and the spine. As such, an MRI of the spine may be useful in the diagnostic workup, but a spinal MRI alone cannot be used to diagnose MS on its own.
MRI is the gold standard for detecting and monitoring the lesions that result from myelin loss in the nervous system and define multiple sclerosis (MS). While an MRI is almost always a critical part of the diagnostic evaluation, MRIs alone are not enough to confirm the diagnosis — other tests are needed to confirm that MS-like inflammation is the cause of the damage, and to rule out other conditions that may mimic MS.
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