Magnetic resonance imaging (MRI) also known as nuclear magnetic resonance tomography, is a procedure that provides high-resolution images of areas within the body.
The following illustrations show images of this kind with typical MS foci in the brain-stem, or around the ventricles of the brain. View related illustration.
A ‘picture’ of the brain
MRI is especially suitable for viewing soft-tissue structures such as the brain or the spinal cord. MRI does not use X-rays but measures tissue behaviour in a strong magnetic field. The measurements are fed into a computer, which converts them into images or scans. This method makes it possible to detect plaques in the central nervous system and provides information on the location and size of the plaques.
What happens during an MRI scan?
During an MRI examination, the patient is asked to lie flat on a special bed, which enters a narrow examination tunnel supplied with extremely high magnetic fields. The procedure can be rather noisy, but is painless, and may require the patient to lie immobile for up to one and a half hours. Contact throughout the procedure is maintained with the operating staff by microphone and earphones. Patients with phobias about enclosed spaces are treated beforehand with anxiety-reductive tablets.
Detecting new foci
This procedure enables both new, active inflammatory foci and old, indurate plaques to be detected. After injection into a vein, a contrast agent such as gadolinium makes it easier to distinguish between new and older foci.
During the later course of the illness, as a result of the increasing impairment of nerve fibres fibres, MRI images also reveal atrophy, when the brain and medulla begin to shrink. On account of the high magnetic field, metal parts are not allowed in the examination room, or in the tomography machine, due to the risk of magnetization. This applies to metal implants, including artificial hips, pacemakers, or post-operative metal clamps.
The head and spinal cord cannot be examined simultaneously during a single session, so it is essential to decide in advance which area of investigation is most important.
MRI often, though not always, makes it possible to detect lesions that are responsible for specific clinical symptoms.
Examinations in the course of the disease also make it possible to discover foci that as yet have not resulted in clinical symptoms. On the other hand, there are very few clinical symptoms that are not associated with a demonstrable focus of the disease.
MRI examinations show that disease foci are ten times more frequently recognised in this way, than in clinically observed episodes.
Two different types of MRI scan
There are two basic types of MRI scans:
Ideally, both T1- and T2-weighted scans are used for a more complete view of the disease activity.
MRI is just one means of detecting MS
MRI is the most significant para-clinical examination used to confirm the existence of MS. Whilst MRI helps physicians to give an earlier and more accurate diagnosis of MS, it is never possible to diagnose MS solely on the basis of MRI results.
Other illnesses can provoke changes in MRI, which are similar to those of MS. In rare cases, even people with no illnesses can present atypical MRI results.
Assessing MS development
In addition to assisting diagnosis, MRI is also of great value in assessing the development of MS. The number and extent of lesions detected during MRI are related to the activity of the disease. Repeated MRI examinations serve to document the long-term course of the illness and, in addition to clinical criteria, help to determine the most appropriate kind of treatment over time.
