Magnetic resonance imaging (MRI) is the preferred imaging tool used to diagnosis multiple sclerosis (MS), and to track the disease’s progression. It is the most non-invasive and sensitive way available of imaging the brain, spinal cord or other body areas.
MRI uses a strong magnetic field and radio waves — but not radiation — to measure the relative water content in tissues, whether normal or abnormal tissues. It creates detailed images of areas to reveal nerve damage (myelin that protects nerves is fatty and repels water, and demyelinated nerves retain more water). A contrast material may be injected in the patient’s veins to highlight lesions, improving their visibility.
How MRI works
Up to 60 percent of the adult human body is water. MRI uses a strong magnetic field and computer-generated radio waves to measure the water content in such body areas as tissues, nerves, organs, and bones.
MRI scanning equipment creates a magnetic field around the body that’s strong enough to temporarily realign a small but significant percentage of the water molecules in tissues. Once aligned in the direction of this field, radio waves then pass through to break this new alignment, allowing the water molecules to relax once the waves stop. As they relax and resume their earlier alignment, their protons release resonance signals that a computer then processes into 3-D images or 2-D “slice” images of tissue.
The distinction in water molecule response between healthy and demyelinated nerve fibers aids in diagnosing and tracking MS, with damaged nerves appearing, depending on type of scan used, as bright white or darker spots.
There are different types of MRI scans:
- T1-weighted scan. In this MRI technique, a contrast material (gadolinium) is injected into the patient’s veins to highlight newer, active areas of inflammation. Gadolinium is a large molecule that only enters the blood-brain barrier when there is active inflammation.
- T2-weighted scan. This is the most common MRI scan used to diagnose MS, and to detect areas of myelin damage (old and new) in the brain and spinal cord.
- FLAIR (fluid attenuated inversion recovery). This type of scan better identifies brain lesions that are associated with MS.
- Spinal cord imaging. This scan technique identifies damage in the spinal cord. It can help to establish a diagnosis of MS by demonstrating that damage has occurred in separate areas of the central nervous system (CNS) at different points in time.
Getting an MRI
Wear loose and comfortable clothing. You’ll be asked to remove your jewelry and other metal pieces (e.g., eyeglass, removable dental work) as they can interfere with the magnetic field. Then you’ll be lie on a table that slides into the MRI scan, and you’ll hear clicking sounds when the magnetic field is turned on and off.
The test is painless, safe, and usually takes between 10 and 60 minutes. People who are claustrophobic may feel uncomfortable and confined, although some scans now do not completely surround the body. But their quality is not yet as high as a standard MRI.
MRI and MS
In MS, the immune system attacks the protective coating (myelin) that surrounds the nerve cells. MRIs are useful in detecting CNS demyelination and in helping to establish a diagnosis of MS.
An MRI scan is also useful for patients with a single demyelination attack, known as clinically isolated syndrome (CIS). In this case, it can identify the number of lesions to assess someone’s risk ofa second attack, or identify a second attack — and so diagnose MS — in a person who has no additional symptoms.
Once a person is diagnosed with MS, MRI scans help in tracking the disease’s progress and in making treatment decisions (whether to continue with a given therapy or change to a new one). Most doctors now recommend follow-up MRIs every year for MS patients.
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