Magnetic Resonance Imaging or MRI
Magnetic resonance imaging (MRI) is an important tool used for diagnosing MS and monitoring disease progression. MRI is a non-invasive imaging technique that is effective in showing the type of CNS damage, including lesions and brain atrophy, common in MS.
What happens during an MRI scan?
A typical MRI machine looks like a very large cylindrical tube into which a patient is rolled (inserted) while laying on a special table often with their head held in a mask-like apparatus. Before entering the MRI machine, you will need to remove anything metal, such as jewelry, hearing aids, or eyeglasses that might have a negative effect on the clarity of the images. The MRI scanner makes very loud banging noises when it is operating, so you may want to wear earplugs or earphones. The MRI technician will communicate with you as each image is taken and you will be able to talk with the technician through speakers at any time during your MRI should you need assistance.
How long does an MRI scan last?
An MRI scan of the brain typically takes at least 45 minutes during which time you will be asked to remain absolutely motionless for anywhere from several seconds to several minutes at a time. If you suffer from claustrophobia, tell your physician and you may arrange to use sedating medication before the MRI scan. Also, some MRI facilities have scanners that are open on both sides. However, these types of scanners tend not to give the same level of clarity as an MRI machine with an enclosed chamber. If you can’t tolerate enclosed spaces and prefer not to be sedated, ask your physician if an open-sided MRI scanner is appropriate for you.
How MRI images reveal lesions and disease activity
Gadolinium (Gd, for short) is a contrast agent which helps to highlight or enhance active lesions on the MRI image, making disease activity more visible. The MRI technician will inject the gadolinium by placing an intravenous needle in your vein mid-way through the MRI scan.
Are there some patients who can’t have MRIs?
Patients who have cardiac pacemakers or certain kinds of metal implants, such as cochlear implants, cannot have MRIs because of the powerful magnets used in MRI scanners. However, not all metal implants cause problems with MRIs, so even if you have metal pins or plates from a prior surgery, you may still be able to undergo an MRI. When you schedule the procedure, the staff at the MRI facility will ask you whether you have a pacemaker, a prosthetic joint, or other kinds of metal implants. Talk to your doctor if this might be an issue for you.
Note that some people with tattoos on their bodies report burning or swelling in the area of the tattoo during or after an MRI scan. This may be due to the fact that pigments in tattoos sometimes contain metallic components. The presence of metal in tattoos may also influence the quality of MRI images.
Are MRI machines safe?
Before development of MRI machines, computed tomography (CT scan) was used to visualize CNS damage caused by MS. However, MRI machines offer several advantages over the CT scan. The CT scan is a specialized x-ray technique, so it exposes a person to a certain amount of radiation. MRI relies on high-powered magnets and not radiation for imaging which makes it safer. MRI scans are more accurate than CT scans and provide clearer evidence of damage to the white matter (tissue) in the brain and spinal cord.
What does the neurologist look for on the MRI scan?
The radiologist and your neurologist look for evidence of new damage, primarily lesions, and evidence of chronic damage to the CNS. New or ongoing tissue damage (see the MRI scans above) may appear as areas of brightness where inflammation is causing damage to the myelin coating on nerve fibers. Gadolinium enhancement allows new active lesions to be distinguished from old ones as recently formed lesions or plaques will appear brighter on the MRI scan. Areas of past nerve damage, or where axons (nerve fibers) have died, may appear as black holes.
Following your MRI scan, be sure to ask your neurologist to discuss the results with you and point out the places in your brain and spinal cord where damage or changes have occurred.