Magnetic Resonance Imaging (MRI) is a scanning tool that used for (almost) every medical condition. The machine (or the ‘tunnel’) uses large tubular magnet to take images of the relevant body part.
The way an MRI is performed is called the MRI technique. Different techniques use different aspects of the MRI to capture certain images. For example, some techniques will show density, like bones as light areas on the picture, other techniques may show it as dark.
The person who does the actual scanning is called a radiographer, the person who interprets the information on the picture is called a radiologist. This interpretation can take a few days to be complete. There is no radiation involved in MRI.
An MRI can capture changes in the brain and spinal cord, so it is an important diagnostic tool for MS. MRI can take images of the brain and spinal cord that show damage to particular areas and damage that has certain characteristics that are consistent with MS. These areas of damage are commonly called lesions. The damage related to MS that MRI can help detect includes lesions, active inflammation and permanent loss of neurons. It is generally thought an MRI doesn’t capture all lesions and activity in MS. As technology advances, the images can be clearer and more detailed and this enables more sensitive detection of MS related change.
It is important to know that lesions and damage can occur in the brain and spine for many different reasons. Lesions can also occur in people with no diseases process but part of normal processes or ageing. These lesions don’t cause any change to a person’s functioning.
A lesion or area of damage is not necessarily associated with a change in a person’s function. People can develop lesions and not be aware of these.
The diagnosis of MS is not usually made just an MRI, but considers other factors such as other diagnostic tools, a person’s medical story and the physical neurological examination.
Two types of MRI scan are generally carried out when looking for MS lesions, inflammation and loss of neurons.
The main type of scan used in the technique known as a T2 image. This is used to help determine the total number of lesions or what is called the overall disease burden. T2 lesions appear as bright whiter spots on the scan which indicate areas where the myelin sheath has been damaged or destroyed. Changes in the brain due to factors such as migraines, or the ageing process also appear as bright spots on a T2 scan, which is why it can sometimes be difficult to distinguish the lesions seen in MS from the normal changes.
Although less useful for diagnosis than a T2 image, the other type of image that can be taken is a T1 image. Areas where nerve cells have been permanently lost or damaged appear as dark areas on this type of scan. A T1 scan can also show areas of swelling (oedema) that aren’t permanent but can reflect active inflammation.
Contrast agents, or Gadolinium (often called dye or gad) is an inert material or contrast agent that when injected into a vein through an intravenous cannula can travel to the brain and highlight areas where cells of inflammation are very active and causing inflammation.
Contrast agents are used in MS as part of diagnosis and then to detect if there is possible relapse activity indicated by active inflammation in the brain and spine. Small amounts of some contrast agents may remain in the brain after a scan.
Studies have found no evidence that these deposits cause any harm long term but recommended using the lowest dose required for a clear image. For this reason, contrast agents are often only used in MS for scans at diagnosis or when someone is suspected to be having a relapse. Routine monitoring scans are usually done without contrast.
When having contrast agents some people will get a metallic taste in the mouth; less than 2% of people might feel nauseated.
Contrast agents used for MRI are different to those used for CT and X-ray contrast studies. MRI contrast agents have lower rates of anaphylactic reaction and are given at much lower doses than those used for CT.
In people with severe renal (kidney) disease there are risks of damage to the renal system with contrast agents. This is rare but serious condition and deaths have occurred. For this reason, your GP or Neurologist may require you to have a blood test before the contrast as a precaution.
There are no significant medical risks associated with MRI, other than it uses a very powerful magnet so all internal and external objects must be removed from your body. Because of this risk, you will be asked to complete a screening form before every MRI.
The loud mechanical vibrations in the scanner can aggravate pre-existing hearing loss and tinnitus. This is usually temporary. While hearing protection is routinely offered to patients, it does not always prevent symptoms
Between 2% and 5% of patients cannot tolerate the enclosed space of an MRI scanner. Most MRI sites can provide sedation (usually intravenous) to patients, where it is medically appropriate
There are no known adverse effects of MRI in pregnancy. It is considered reasonable to perform MRI during pregnancy if the result is required for management during pregnancy and is not available from other tests. Otherwise, it is prudent to defer the MRI scan until after pregnancy (or at least after the first trimester)
MRI contrast agents are relatively contraindicated in pregnancy
Breastfeeding is not a contraindication to MRI or MRI contrast agents. It is not necessary for women to stop breastfeeding before or after an MRI, nor does breast milk need to be manually expressed and discarded after MRI.
Visit the Royal Australian College of General Practitioners website for more information on possible contraindications.
MRIs are an important part of monitoring MS activity and most people with have an MRI at least once a year.
For some people, the smaller space in an MRI and the loud banging and buzzing sound of the machine can make them feel anxious or nervous. Below is some information and advice to help make your scan a smoother experience:
Many centres will now provide you with a copy of your MRI on a disc or a link to access the MRI via your mobile phone or online. It is very useful to have copy of your own scans to take to our neurologist or to keep with you if you are travelling long term or consider changing medical services. You can also ask for copies of reports.
For routine monitoring, it is generally discouraged to change the medical imaging centre where you have your scans done as machines can be slightly different and comparisons form your last scans are vital to monitor your progress. There may also be reasons why you need to change, such as accessing a more advanced MRI machine. You can ask your Neurologist about this.
To understand your MRI results it takes Neurologists and Radiologists working together to understand the results of the scan. It’s challenging and complex to interpret a scan, so if you are interested in understanding your MRI its best to ask your Neurologist or MS nurse to talk you through it and explain it to you.