Magnetic Resonance Imaging (MRI)

From The MS Information Sourcebook, produced by the National MS Society.

The magnetic resonance imaging (MRI) scan is a diagnostic tool that currently offers the most sensitive non-invasive way of imaging the brain, spinal cord, or other areas of the body. It is the preferred method of imaging to help establish a diagnosis of MS.

Relies on Magnetic Fields, Rather than Radiation
Unlike a CAT scan or conventional X-ray, this type of scanning device does not use radiation. Instead, it uses powerful magnetic fields that interact with the hydrogen atoms found in the water contained in all body tissues and fluids. Computers translate the increased energy of the hydrogen nuclei into cross-sectional images.

The scanning procedure is very sensitive, and can often detect lesions—damaged areas—that would be missed by a CAT scan. A contrast agent (gadolinium) can be injected into a patient intravenously to further enhance the sensitivity of the MRI scan. Although the absence of radiation is an asset, the powerful magnetic fields of MRI prohibit its use with people who have cardiac pacemakers, or metal, such as aneurysm clips, implanted in their bodies.

Particularly Useful in Detecting Demyelination
MRI is particularly useful in detecting central nervous system demyelination, and thus it is a powerful tool in helping to establish the diagnosis of MS. Demyelination or the destruction of myelin—the fatty sheath that surrounds and protects nerve fibers—causes nerve impulses to be slowed or halted and produces the symptoms of MS.

A group of neurologists who specialize in MS formulated a policy statement for the National MS Society in 1986 that reads: "MRI is the preferred imaging technique in the diagnosis of MS." Studies have repeatedly demonstrated that MRI of the brain can reveal areas of demyelination that are not apparent on a CAT scan.

It should be remembered, however, that approximately 5% of patients with clinically definite MS do not show lesions on MRI, and the absence of demyelination on MRI does not rule out MS. Also, since many lesions seen on MRI may be in so-called "silent" areas of the brain, it is not always possible to make a specific correlation between what is seen on the MRI scan and the patient's clinical signs and symptoms. In addition, people over the age of 50) often have small findings on MRI that resemble MS but are actually related to the aging process and have no clinical significance.

May Prove Useful in Tracking Progress of the Disease
While MRI may be useful in helping to confirm a diagnosis of suspected MS, it cannot, by itself, diagnose MS. Once a positive diagnosis of MS has been established, there is no reason why an MS patient should have further diagnostic MRI scans. Subsequent scans, however, may prove useful in tracking the progress of the disease, or possibly helping to establish a prognosis—a prediction of the course of a disease. For example, some researchers have demonstrated that the degree of cognitive impairment as demonstrated by neuropsychologic testing can be correlated with the amount of demyelination seen in certain areas of the brain on MRI.

See also...

• Cerebrospinal Fluid (CSF)
• Diagnosis
• Diagnosis Of Demyelinating Diseases
• Evoked Potentials
• Medical Histories
• Symptoms

Last updated April 2003