Epilepsy Awareness Program - MRI


Although epilepsy is defined as recurring seizures, its diagnosis may be more difficult for some patients. Even when diagnosed, some patients do not respond to medications. New research in imaging techniques may help those patients with difficult diagnoses or treatment plans.

Magnetic resonance imaging also called MRI provides details about the brain. MRI may detect certain lesions (diseased tissue) in the brain that cause seizures. MRI also helps specialists diagnose the causes of epilepsy and evaluate potential candidates for surgery.
Brain abnormalities may be subtle. Specialized MRI scanning may detect asymmetries (dissimilar corresponding parts on opposite sides that are normally alike) in the brain that indicate the side of the brain where seizures begin.




MRI and Epilepsy

Epilepsy is defined as having two or more seizures without an identifiable cause. A seizure occurs when something disturbs the pattern of electrochemical signals and causes the nerve cells in the brain to fire much faster than normal. This storm of electrical activity in the brain can result in changes in mood or behavior, hallucinations, involuntary muscle contractions or loss of consciousness.
MRI, short for magnetic resonance imaging, is one of several tests used to diagnose epilepsy, in addition to blood tests and an electroencephalogram (EEG). The MRI device uses magnets and radio waves to produce detailed images of your internal tissues. When testing for epilepsy, the MRI may detect brain abnormalities through its images.
Despite the multiple diagnosis methods available, doctors may still have trouble identifying the part of your brain where the seizures occur. You may still receive medications to prevent the seizures, but they do not always help. However, without a clear diagnosis, further treatment options are limited.
Newer MRI techniques may help improve epilepsy diagnoses. Two techniques developed by British researchers focus on water in the brain. One technique examines water movement through the brain and the second examines how water interacts with proteins.
These new methods have proven their effectiveness. When testing for epilepsy, the new techniques have found signs of epilepsy in 29 percent of people who showed no evidence of the condition through standard MRIs. The new techniques may help pinpoint where the seizures occur in the brain and detect post-seizure brain damage.
In addition to diagnosing epilepsy, these new techniques can also help treat the disease. Medications prevent the seizures for most patients, but some people need surgery. However, surgery options are limited if doctors cannot identify the area of the brain where the seizures occur. These new MRI techniques improve accuracy in locating where the seizures occur and allow for the possibility of removing that part of the brain.
While these new MRI techniques are not effective for everyone, they hold promise for improving the lives for many people living with seizures.


Use of MRI in diagnosis of Epilepsy

When a magnetic resonance imaging (MRI) scanner is used to investigate epilepsy, it takes detailed pictures of patients head. It can help to find if there is an abnormality that might be causing epilepsy, for example, scar tissue due to a brain injury.
The MRI will send images of your brain to a computer, which will show different types of brain tissue in different colours.
Patient may be injected in his/her hand or arm, with a harmless dye, to make the tissue show up more clearly.
The MRI is the most common scan used for individuals with epilepsy, particularly if any of the following applies:

If you have developed epilepsy before the age of two years or in adulthood; or
If you could have damage in the brain to cause the seizures; or
If you continue to have seizures despite taking medication.

The MRI will look for an abnormality in a specific area of the brain, which may be the cause of the seizures.
An MRI is not always used for people who have generalised seizures. This is because epilepsy is unlikely to be caused by structural damage, when epileptic activity starts in both sides of the brain. Therefore, the scan is unlikely to add anything to the diagnosis. Also, an MRI is not usually needed for people with some epilepsy syndromes, such as benign rolandic epilepsy. Again, this is because these types of epilepsy syndromes are not associated with an abnormality in the brain.
The MRI scan can take up to an hour and is very noisy. In the middle of the scanner is a hollow tube. You will be asked to lie on a table which is then moved inside the tube, which will scan your head and take pictures.
The scanner is operated from behind a window by a radiographer. After the scan a radiologist will interpret the pictures taken by the MRI. These results will then be send to your doctor who arranged the scan.
MRI scans may not be suitable for people who have had a vagus nerve stimulator (VNS) or metallic clips implanted in their brain. There is a risk that the MRI scan could heat up the wires in the VNS or the metallic clips and cause damage to the surrounding tissue.
Some people with a VNS or metallic clips choose to wear identity jewellery, so medical professionals would be aware of this if they ever needed to have an MRI scan.

Before an MRI

If you will be given a sedative, you should not eat or drink approximately 4 hours prior to the exam.
Take all prescribed medication(s) as usual.
Wear loose, comfortable clothing.
Remove all metallic devices (watches, jewellery, hairpins, glasses, hearing aids, removable dental work) before the examination. Metallic devices can cause a bright or blank spot on the picture.
It will be much easier for you to relax during the examination if you avoid caffeine drinks before the test.
If you are claustrophobic (fear of being in closed-in spaces), be sure to inform your doctor before taking the test.

During an MRI

You will be asked to provide the technologist about your medical history.
You will lie down on a cushioned table that will slide towards the machine so the head is inside its circular opening.
You will need to lie flat and still as you move through a narrow cylinder.
You may have someone stay with you during the procedure because there are no known risks to those in the room with the machine.
You will be able to speak to the technologist during the examination via an intercom.
You should remain still, relax and breath normally as the images are taken. Any movement during this time will blur the images.
You will not feel anything during the examination but may hear thumping sounds from the MRI equipment. These noises may be a little unsettling at times, but they are a normal part of the MRI procedure.
In some cases, your physician may request an MRA (Magnetic Resonance Angiography) in addition to your MRI exam. This exam provides an analysis of your vascular system and major blood vessels. Usually, the MRI and MRA are completed in the same visit.
The MRI procedure usually lasts anywhere from 30 to 90 minutes.

After an MRI

There are no harmful side effects after the examination and you may return to your normal activities and diet immediately after the scan.
If a sedative is administered, you will be monitored until the effects of the sedative subsides. You will then need a friend or relative to drive you home.
The MRI scan will be reviewed by the radiologist who will send a report to your physician.
After the physician receives the results of the test, they will confirm a diagnosis or prescribe further tests and treatments.

Additional Types of MRIs

Functional MRI (fMRI)
is a non-invasive technique that provides both an anatomical and functional view of the brain. Similar to the MRI, fMRI uses magnetic fields instead of x-rays to produce detailed pictures of the brain. This technique allows us to localize specific areas of brain function by imaging patients while they perform specific tasks. Therefore, functional MRI can identify regions of the brain that are active during cognitive, sensory, and other tasks by detecting changes in blood flow to particular areas of the brain. This information is often very useful to the neurosurgeon; it helps physicians identify the exact location of the source of the seizures.
The advantage of using an fMRI is that it can measure blood flow without using radioactive tracers. Instead, fMRI takes advantage of the fact that haemoglobin, an oxygen carrying molecule in the blood, contains an iron molecule which has magnetic properties. When a magnetic field is presented to the brain, the haemoglobin molecules line up, like tiny magnets. fMRI indicates the presence of brain activity because the haemoglobin molecules in areas of high brain activity lose some of the oxygen they are transporting. This makes the haemoglobin more magnetic, thereby responding more strongly to the magnetic field. The fMRI machine determines the relative activity of various areas of the brain by detecting changes in the magnetic response of haemoglobin.

- - - { Advantages of fMRI }:


It can look at discrete areas of brain activation
The final image depicts more detail than CT scans
It can measure fast-changing physiology better then the PET scan.

Magnetic Resonance Spectroscopy (MRS)
It gives information about the chemical and physiological information about certain structures in the brain.
The "open" MRI is a new design with an extra large opening. This allows more airflow and an open view around you during the examination. This open design is good for those who are claustrophobic because it allows you to feel less enclosed and confined, thus, minimizing anxiety. Because of the open view, this system provides enough room to image patients weighing over 500 pounds. In addition, the "open" MRI allows you to be accompanied throughout the examination by a family or staff member.


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See Also: Epilepsy Health Corner

See Also: Neurophysiology Health Corner

Back to: Epilepsy Awareness Program

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