The Role of MRI in an MS Diagnosis

“MRI is critical in the diagnosis of MS,” says Robert Zivadinov, MD, PhD, a professor of neurology and biomedical informatics at the University of Buffalo’s Jacobs School of Medicine and Biomedical Sciences in New York. “MRI is used to determine your prognosis over short-, mid-, and long-term, and [it] plays an important role in determining treatment efficacy.”

Unlike a computerized tomography scan or X-ray, MRI doesn’t use radiation — rather, it employs magnetic fields and radio waves to measure the relative water content in your body’s tissues.

In MS, your body’s immune system attacks the myelin sheath in error. Because the layer of?myelin?that protects nerve cell fibers is fatty, it naturally repels water. However, in the areas where the myelin has been damaged by MS, fat in the sheath is lost, meaning it holds more water.

These water-rich areas of damage, called lesions, are visible on MRI.

The number of lesions on an initial MRI of the central nervous system can help assess your risk of developing a second attack in the future and of being diagnosed with MS.

MRI can also spot a second demyelinating attack, even if you have no other MS symptoms. This can help confirm an MS diagnosis early in the course of the condition.

In addition, some people age 50 and older may have small lesions on their MRIs that resemble those seen in MS but that are in fact related to the aging process.

People with migraine may also have similar lesions.

For these reasons, while MRI remains important in the diagnosis of MS, it’s not the only criteria your doctor will use. They will also examine you for the presence of any clinical signs or symptoms of MS, as well as ask about any family history you may have of the condition.

They will also conduct a routine neurological exam, and in some cases, they’ll conduct additional tests — such as a lumbar puncture (spinal tap) — to rule out other conditions or to look for evidence to support a diagnosis of MS.

MRI scans are done in a few different ways, depending on the machine being used, and the reason the imaging is being done.

Teslas

Named for the scientist Nikola Tesla, this unit of measurement indicates the strength of a magnetic field. In the case of MRI, it essentially refers to the strength of the magnetic field produced by the machine.

The stronger the magnetic field (more teslas), the better the resolution of the images the machine can produce, meaning your doctor can better see any lesions that may be a sign of MS.

Although 1.5T MRI is considered the minimum for use in MS diagnosis, most medical facilities in the United States are moving to 3T, or 3 tesla, MRIs, according to Dr. Zivadinov.

Most MRI machines that are 3T and above are “closed,” meaning you will be placed in a capsule-like space, lying down, during the scan.

“3T is superior because of higher contrast-to-noise ratio,” Zivadinov explains. This increased resolution, or better image quality, gives your doctor the “ability to detect about 30 to 40 percent more lesions compared with 1.5T MRI,” he adds.

Contrast Dye

In addition to magnetic field strength, another factor to consider with MRI is the use of contrast. In a contrast MRI, the medical team will inject a fluid containing gadolinium, a type of metal, into one of your veins.

Current guidelines recommend the use of contrast MRI for the initial diagnosis of MS or to assess progression or relapse in certain types of the condition, according to Zivadinov.

By itself, gadolinium is toxic, which is why manufacturers add other chemicals to the contrast dye to blunt gadolinium’s effects. Still, even with these steps, contrast dyes can cause side effects — in rare cases — such as:

• Hives or rash
• Kidney problems
• Difficulty breathing
• Cardiac arrest
• Anaphylactic shock

People who are pregnant or breastfeeding shouldn’t undergo a contrast MRI.

Your doctor may perform a blood test — in particular to look at kidney function — and other assessments to determine your risk for these and other side effects. People with kidney disease can have a harder time metabolizing the contrast.

Because of this, “use of contrast has been dropping in the imaging of MS patients,” Zivadinov says. But MRI can still be used, without contrast, to diagnose and assess MS, he adds.

T1-Weighted vs. T2-Weighted

In an MRI without contrast, areas of active inflammation will show up bright on T2-weighted images, according to Zivadinov.

And that is another term you may hear in connection with your MRI: T1-weighted or T2-weighted. In this case, the T stands for time, and it refers to the amount of time between the application of a radiofrequency pulse and the measurement of a signal in MRI.

T1-weighted MRIs use a shorter amount of time between application and measurement, which results in images that highlight the differences in tissue density and water content.

FLAIR Sequences

MRIs are most often used in MS to spot brain lesions, or damage to the myelin sheath, which are a hallmark of the disease.

When enough myelin is lost from enough nerve fibers in an area, the water-rich lesions are visible on MRI, either as a bright, white spot or as a darkened area, depending on what type of MRI is used.

“The presence of two lesions in different areas of the central nervous system, or CNS, which includes the brain, spinal cord and optic nerve” can result in an MS diagnosis, Zivadinov says.

This meets the so-called “dissemination in space” diagnostic criteria for MS, which means damage is occurring in multiple parts of the CNS, he says, adding that “lesions in the brainstem, spinal cord, or optic nerve are more likely to produce the signs and symptoms of MS.”

The McDonald criteria for the diagnosis of MS also indicates that an MRI revealing evidence of damage to the CNS “disseminated in time,” or related to more than one demyelinating attack, likely means the person has the condition.

MRI can also help your MS care providers track the progression of the disease and make the best decisions for your treatment.

These follow-up MRIs can help determine how well your treatment is working and whether you may need to change it.

In general, disease-modifying therapies help prevent the development of new white matter lesions and, hence, symptom relapses and disease progression.

Aside from the side effects associated with the use of contrast agents cited above, MRI is safe for most people, even if you’ve had heart surgery or have had the following devices implanted:

• Artificial joints
• Surgical staples
• Brain shunt tubes

Unlike X-ray, there’s no radiation involved in MRI, meaning no risk for exposure.

Possible Risks

• Older heart pacemakers
• Older (metal) cerebral aneurysm clips
• Older implanted spine stabilization rods
• Implanted drug infusion pumps
• Pain medication pumps or implanted spinal cord stimulators for chronic pain
• Cochlear implants for hearing impairment

In addition, anyone who has internal metallic objects such as bullets or shrapnel, as well as surgical clips, pins, plates, screws, metal sutures, or wire mesh should alert their doctor about these before scheduling an MRI.

Talk to your doctor if you don’t feel you’ll be able to lie on your back for an hour or more or if you have claustrophobia, or a fear of tight spaces.

Finally, there may be other risks, depending on your health history. Talk to your doctor about any concerns you may have before having an MRI.

• MRI is a powerful imaging tool that can detect tissue changes related to multiple sclerosis, aiding in both diagnosis and tracking disease progression.
• MRI can be done in a few different ways, to better visualize different types of MS lesions.
• MRI is generally safe, but it's important to discuss any metal implants or specific health concerns with your doctor beforehand.