What is Magnetic Resonance Imaging (MRI) in Multiple Sclerosis (MS)?
MRI is a test that provides images of the body (brain and spinal cord in MS) using strong magnetic field and radio waves, but not radiation. The scan may take between 30 to 60 minutes and can get thousands of brain images. A contrast material, called gadolinium, may be injected intravenously in the patient, to highlight lesions.
Magnetic resonance imaging allows earlier diagnosis and treatment, as well as monitorization of the progression of MS by keeping track of any new lesions that may have occurred since initial diagnosis.
Also, certain MRI imaging data obtained early in the disease course can serve as prognostic markers. A lesion number, volume and distribution can be useful for predicting the long-term outcome of MS.
How can Magnetic Resonance Imaging support MS diagnosis?
There´s no single definitive test that can diagnose multiple sclerosis. If you have typical symptoms of MS, your neurologist may order an MRI scan of your central nervous system (brain and/or spinal cord).
Diagnosis is based on symptoms, clinical evaluation, and a series of diagnostic test to rule out other conditions (blood test, cerebrospinal fluid test, central nervous system MRI).
MRI is the best technique in the detection of demyelinating lesions, of the central nervous system, in patients with MS. It´s not only essential during diagnosis, but also a prognostic marker in the initial phase of the disease.
It`s important to note that the number of lesions shown on an MRI scan doesn`t always correspond to the severity of the symptoms.
Typical lesions that favour MS included small and ovoid lesions throughout white matter, corpus callosum lesions, infratentorial areas (pons and cerebellum) and a spinal cord lesion. However, other white matter diseases can have similar appearances during an MRI scan, such as vascular disease, autoimmune diseases, migraine, and unspecific images.
According to the most recent recommendations, an early MRI scan of the spinal cord would be useful in MS. Spinal cord lesions are common in MS and their detection is useful as a prognostic tool. 
Use of Magnetic Resonance Imaging to follow-up or track disease progress
Your neurologist may recommend additional MRI scan of the brain, at certain intervals, to monitor disease activity and progression. The frequency and type of monitoring depends on individual case (type of MS, disease activity, treatment,). It´s advisable to compare across studies or between centres.
When possible, follow-up MRIs should be obtained on the same scanner as this will help the radiologist and neurologist make a comparison from one MRI scan to the next.
On the order hand, MRI can help predict treatment response and assess the efficacy of therapies immunomodulatory and/or immunosuppressive drugs for the treatment of MS.
According to the most recent consensus, a spinal cord MRI is not recommended in the routine follow-up.  Neither, gadolinium use is recommended in the routine follow-up: European Medicines Agency recommended that gadolinium should be used only if essential, and at the lowest possible dose. 
In general, MRI is not necessary to diagnose a relapse, and it should rather be a clinical diagnosis.
What are active lesions in a Magnetic Resonance Imaging test?
New lesions, appearing in an area that was of normal tissue during a previous MRI, and contrast-enhanced lesions are classified as active lesions.
Enhancement in inflammatory demyelination lesions is reversible, typically < 4 weeks in most cases. 
It reflects the inflammatory component of the disease.
Active lesions don´t always relapse, however the disease is cannot be fully controlled.
What is the Lesion Load?
The number or volume of lesions is called the “lesion load”. The traditional evaluation is based on a radiologist´s visual inspection, although automatic analyses of MRI scans may provide faster assessments. Lesion count is difficult to assess when there are confluent (i.e.. overlapping) lesions.
Some researchers propose counting lesions as follows: 0-20 lesions, 20-50 lesions, 50-100 lesions, >100 lesions and confluent lesions. When there are up to 20 brain injuries, they will be identified one by one visually, above this amount the count will be approximate and will be done in the form of ranges. 
The principles of MS diagnosis are based on showing dissemination of lesions in space (DIS) and time (DIT) (Mc Donald criteria ).
Disseminated in time classified as damage (new MRI damage or clinical relapse) occurs on different dates, over the course of time.
Disseminated in space classified as plaques occurring in multiple parts of the central nervous system.
What are “black holes” in a Magnetic Resonance Imaging test?
‘Black holes’ appear as dark areas on the MRI.
They are chronic lesions, areas of irreversible tissue damage.
What is brain atrophy?
In MS there may be a loss of brain volume which is called atrophy.
As the person ages, they naturally lose some brain cells, but this is a slow process. Brain atrophy associated with disease occurs quicker (premature brain aging).
Brain atrophy can be seen in the earliest stages of MS, progresses faster compared to healthy adults, and can be a predictor of future disability. It reflects the neurodegenerative component of the disease.
What is the Radiologically Isolated Syndrome (RIS)
RIS is the detection of abnormal brain findings, like what is seen in patients with multiple sclerosis, but without the typical neurological symptoms. Diagnosis of RIS often occurs during the diagnosis of other unrelated condition, such as migraine headaches or trauma.
Being diagnosed with RIS doesn´t mean a patient will necessarily be diagnosed with multiple sclerosis.
Patients will have routine check-ups to evaluate if their condition is progressing toward MS.
- 2021 MAGNIMS-CMSC-NAIMS consensus recommendations on the use of MRI in patients with multiple sclerosis. The LAcet Neurology, 20(8), 653-670. Wattjes, MP, Ciccarelli, O, Reich, DS et al. Doi: 10.1016/S14-74-4422(21)00095-8
- Recommendations for using and interpreting magnetic resonance imaging in multiple sclerosis. A Rovira, M Tintore, J.C. Alvarez-Cermeño, G Izquierdo and J.M Prieto. Neurologia. 2010; 25(4):248-265
- Recommendations for the coordination of Neurology and Neuroradiology Deparments in the management of patients with multipla sclerosis. S. Llufriu, E. Agüera, L. Costa-Frossard, et al., Neurologia, https://doi.org/10.1016/j.nrl.2021.01.012
- Diagnostic criteria for multiple sclerosis: 2010 Revisions to the McDonald criteria. Polman CH, Reingold SC, Banwell B et al. Ann Neurol. 2011 Feb; 69(2): 292-302. Doi: 10.1002/ana.22366