If you have MS then I’m sure that you are intimately familiar with MRI machines! MRI’s are the single best way for your health care providers to track disease progression, and to evaluate if your medications are working well. In the past if an MRI showed new lesions, but there were not any new symptoms we would take a “wait and see” approach. However, new evidence is telling us that we should treat the MRI, even if no new symptoms are present. Dr. Vollmer of the Rocky Mountain MS Center says that allowing new lesions to accumulate and basing treatment only based on symptoms is like closing the barn door after the horse has bolted. Once enough damage occurs the person will inevitably have a relapse, and once that happens there is nothing we can do to reverse that damage. Therefore, it makes sense that we would want to prevent damage from occurring in oder to prevent a major event down the line. Last year I switched my medications because my spinal cord showed new lesions and atrophy. I didn’t have any new symptoms, but both my doctor and I felt that I was accumulating too much new damage. We decided to take a proactive approach and switched my medications so that I had the best chance at continuing to feel fine in the future. It can be a bit tricky to decide what to do when there is a discrepancy between symptoms and the results of an MRI but it is important to have MRIs done, even if we feel good.
All of us know that we get MRIs periodically, but not many of us know how they work or what exactly they show. That got me thinking, this could make an excellent educational blog post! You are a brilliant group of people, and you know how much I love expanding your MS knowledge. I truly believe that knowledge is power, so today I want to take some time to teach you how MRIs work, why they make such a ruckus, and what they tell us about MS.
How do MRI’s work?
The human body is mainly made of water and fat (I know, how flattering). As most of you probably learned in grade school, water is made up of hydrogen and oxygen (H2O). An MRI scan focuses on all of the hydrogen atoms within the body. Normally they are spinning around in random directions like a spinning top, but when you put a big powerful magnet next to them they snap to attention and align with the magnetic field. Next, pulses of radio frequency are applied which knock the hydrogen out of alignment with the magnetic field. The radio frequency is then shut off, and the hydrogen atoms snap back to attention once again. The pulsing of the radio frequency is what makes the loud noises, and the periods of silence occur when the pulse is shut off and the hydrogen atoms are realigning with the magnetic field. The movement of the hydrogen is sensed and recorded by the MRI machine, which allows the computer to assess how the liquid within our tissues behave.
The picture above is an MRI image of the brain. Air and bone appear dark because they have a low water content (but there are certain types of MRI scans where they appear bright), while things with a high water and/or fat content such as spinal fluid, blood, brain tissue are brighter. Although bone is dark on MRI scans, the fatty bone marrow also appears white which is why you can see the outline of the skull. Demyelination increases the water content of surrounding tissue, which is why lesions show up as bright white spots. Additionally, contrast dye lets us know if demyelination is new or old.
What are their limitations?
Images are captured in slices and a scan is made up of several slices put together, much like a loaf of bread. This lets health care providers look at a very detailed picture of all the structures, as if they were picking up slices of a loaf of rye bread and inspecting its marbling. However, in the process of cutting slices the MRI may miss some tissues because of gaps between the slices.
There are different resolutions, or strengths, of MRI’s. We like the highest resolution possible because they have very minimal gaps between slices. It is important to consistently get MRI’s on a high resolution machine, otherwise we may not know whether lesions are new or if they were just missed because a lower resolution MRI machine was used.
Being able to compare images from previous years is essential to making decisions about medications, so it can be very frustrating when previous MRIs are not high quality. During the ECTRIMS/ACTRIMS conference in Boston leading experts were discussing the importance of using the standardized the MRI protocol, so that all MS patients have the same type of images no matter where they are being treated. The Consortium of MS Centers has a standardized guideline available on their website.1-3
So that’s probably more then you ever wanted to know about MRI’s, but it’s sort of interesting I think! Any questions??