Magnetic resonance imaging, commonly known as MRI, is a non-invasive diagnostic procedure that produces detailed two- or three-dimensional pictures of the brain by using radio waves, magnets, and a computer. MRI may be used to diagnose epilepsy when EEGs do not provide sufficient explanations for the seizures or symptoms a patient experiences.
On this page, you’ll learn all about the basics of MRI, including its use in epilepsy, the different kinds of MRI techniques, the practicalities of having the procedure done, and lastly, questions to discuss with a doctor before getting an MRI.
Magnetic resonance imaging (MRI) creates images or scans of your brain and is used to detect if there is scar tissue or damage in the brain that could be contributing to the seizures. MRIs, along with other tests, can be used to pinpoint the diagnosis of a person’s epilepsy and is extremely useful if there is structural damage (or “lesion”) contributing to seizures.
MRI can also help visualize brain tumors, defects in the way the brain has developed, and defects in blood vessels in the brain.
The patient will lie on a bed that enters the scanning machine, a horizontal tube about 5 feet long. The machine houses a strong magnet which creates a magnetic field when an electrical current passes through it. MRI scanners use two components – magnetic fields and radio waves – to create an image of the brain.
Our body is made up of about 65% water, which is a chemical compound made of two hydrogen atoms and one oxygen atom (H2O). Each hydrogen atom has one proton with a positive charge that acts like a magnet. When they’re inside a magnetic field, the hydrogen protons orient themselves much like a compass needle orients itself north. During this process, the protons “line up” and generate a magnetic field that can be measured.1
The MRI scanner then flips off the magnet and generates a radio frequency pulse (radio wave) which causes the atoms to scatter. The magnetic field is turned back on and the hydrogen atoms snap back into alignment, again generating energy that can be read by the machine. Different types of tissue and/or fluids give off varying amounts of energy. The machine is linked to a computer that calculates the amount of energy released and is used to create a highly detailed image of the brain or other parts of the body.
There are different settings or sequences, that can be used during an MRI scan. Each of the sequences produces a different type of image, so your physician will instruct the radiology technician on which sequence they want to be used for your MRI. You may hear terms like T1-weighted, enhanced T1-weighted, T2-weighted, fMRI (functional MRI), and FLAIR MRI. These are all names for various types of MRI scans. You will not need to do anything differently; the radiology technician selects the type of scan that the machine will conduct.
An MRI scan produces a clear picture of the brain that helps the specialist understand whether there is a physical injury or abnormality that is causing the seizures. While electroencephalograms (EEGs) are the most commonly used test to diagnose epilepsy, they record the electrical activity of the brain and do not give your physician an understanding of its structure.
For certain types of epilepsy (for example, traumatic brain injury) where an injury is suspected, an MRI is performed to get details on where the seizure may be originating from.
Because MRIs may be able to pinpoint the specific location in the brain where your seizures occur, they can help determine if you are a candidate for epilepsy surgery.
The magnetic field and radio waves used in MRI scans are safe and do not hurt, so you will not feel anything inside the scanner.
Before the scan, the physician will ask you questions about your medical history, including if you have metal in your body (including but not limited to vagus nerve stimulators, pacemakers, and body piercings), tattoos with metallic ink, or if you are pregnant/breastfeeding. It may be dangerous for people with metal in their bodies to get an MRI, and certain pregnancy stages may be better for an MRI than others. Making the physician and MRI technicians aware of any relevant conditions will allow them to make the process as safe as possible.
MRIs produce very detailed 2-dimensional and 3-dimensional pictures of the brain. These images may assist the physician in finding the cause of the seizure, especially if there is a physical (structural) cause.2
MRIs have the ability to show:2
MRIs are particularly helpful for people who have focal seizures. If the seizure starts in a specific place, the MRI may be able to locate the focus. This same technique may be used to determine if a patient is a candidate for epilepsy surgery – the MRI, along with other scans, helps the neurosurgeon identify the exact area(s) of the brain which should be removed or where the cells should be destroyed (ablation).
Functional MRIs (fMRI) can show brain activity by looking at blood flow. When an area of the brain is in use, the blood flow to that area increases. This is particularly helpful for epilepsy surgery candidates because the neurosurgeon can use it to see and map critical areas of the brain for language and memory so that they are avoided during surgery or ablation.3
MRIs are performed at hospitals or designated outpatient imaging facilities. Before the scan, patients are instructed to wear a hospital gown and remove all metal items, such as jewelry and piercings, to avoid a reaction with the electromagnet.
The technician will operate the machine from an office within the MRI room, but the patient and technician can speak throughout the exam. Patients with claustrophobia should let their physician know before the scan begins so that they can make necessary accommodations.
The exam starts on a flatbed which then slides into the scanner. When the scanner starts it will be quite loud, so headphones may be provided to the patient to distract from the noise. The technician will instruct the patient through an intercom if necessary. For example, the technician may ask you to keep very still or hold your breath for a few seconds to help get a clearer picture. You will have access to a “panic button” in case you need to speak to the technician or stop the scan.
An MRI scan usually takes around 30 to 60 minutes, but can take up to 2 hours depending on the complexity of the scan. The scan results take a few days to analyze and are sent to the physician that ordered the test for you.
The following questions and topics may come in handy when you talk to your doctor about getting an MRI: