By: Clara O’Hara
What is an MEG Scan?
An MEG Scan, also known as a magnetoencephalography, is a non-invasive medical test that uses a superconducting quantum interference device (SQUID) and a computer to measure neuromagnetic activity within the brain. It detects, records and analyzes the magnetic fields produced by electrical currents in the brain. The distribution of these magnetic fields is superimposed with an anatomical image of the brain to help identify the source of activity in the brain. An MEG study is a direct measure of brain function and the most advanced method of recording and evaluating the brain while it is actively functioning.
What can an MEG diagnose?
MEG is used to identify or map:
- the functional areas of the brain, including centers of sensory, motor, language and memory activities
- the precise location of the source of epileptic seizures
MEG creates a roadmap of the brain that is useful for preoperative and treatment planning for individuals with epilepsy and for patients undergoing surgery to remove a brain tumor or other lesion. MEG is also used as a research tool to help scientists better understand human brain function and to study neurological and psychiatric disorders.
MEG and Epilepsy
For patients with epilepsy, MEG helps pinpoint the origin of their epileptic discharges without intracranial insertion of electrodes. When implantation of intracranial electrodes is necessary, MEG can help to better plan the exact implantation site.
In epilepsy, MEG can show the propagation of activity from one brain region over a few milliseconds or during the onset of a seizure. MEG results are coregistered with anatomic images from MRI and are reconstructed three-dimensionally to show the exact areas of activity.
MEG vs. Other Magnetic Resonance Imaging Techniques
Like EEG, MEG records the electrophysiological effect of neuronal activity over time; however, with its higher sensor count and simpler modeling physics, MEG has a higher source resolution.
Additionally, recordings with MEG are reference-free; its signals are not attenuated by bone and multichannel, whole-head, high spatial-density recordings are easily obtained. By its very nature, MEG shows areas of function: It localizes the signals generated by neurons as they are activated, as they communicate and as activity spreads through them.
MEG is sometimes called a functional imaging test, but it differs in significant ways from other such tests:
- The functional tests available at most centers are indirect measurements, dependent on changes in oxygen consumption (fMRI), glucose uptake (PET) and blood flow (SPECT). Conversely, MEG measures neuronal activity directly.
- While PET and fMRI measure changes in metabolism and blood flow, respectively, over many seconds, MEG measures electrical activity millisecond by millisecond.
A MEG scan is noninvasive and painless. With no injections, radioactivity or strong magnetic fields, MEG is safe for children and adults. Unlike with some imaging tests, the machinery is quiet and almost never produces a feeling of claustrophobia. During MEG testing, brain activity is ordinarily recorded in both wakefulness and sleep.
Risk of Having an MEG
The MEG examination poses no known risk to the average patient when appropriate safety guidelines are followed.
People with the following implants may not be able to have a MEG exam:
- cochlear (ear) implant
- some types of clips used for brain aneurysms
- some types of metal coils placed within blood vessels
- nearly all cardiac defibrillators and pacemakers
- artificial heart valves
- implanted drug infusion ports
- artificial limbs or metallic joint prostheses
- implanted nerve stimulators
- metal pins, screws, plates, stents or surgical staples
How to Prepare for an MEG
Your physician will advise you on eating and drinking before your exam and whether you may take medications as usual. You may be asked to wear a gown during the exam or you may be allowed to wear your own clothing if it is loose-fitting and has no metal fasteners.
Items that should be removed or left at home prior to the exam include:
- jewelry, watches, credit cards and hearing aids, all of which can be damaged
- pins, hairpins, metal zippers and similar metallic items
- removable dental work
- pens, pocket knives and eyeglasses
- body piercings
- underwire bras
- some types of heavily applied facial make-up, especially around the eyes
What to expect during an MEG scan
If you are feeling anxious about your exam, you may want to ask your physician to prescribe a mild sedative prior to your scheduled examination. Infants and young children may require sedation or anesthesia to complete an MEG exam without moving. Whether a child requires sedation depends on the child’s age and the type of exam. Moderate and conscious sedation can be provided at many facilities. A physician or nurse specializing in sedation or anesthesia for children should be available during the exam for your child’s safety. You will be given special instructions for how to prepare your child for the sedation or anesthesia.
Before the exam the patient will be fitted with three or more head positioning coils. These are small and are painlessly affixed to the head with tape. Their purpose is to determine the precise position of the head relative to the MEG detectors during the scan itself. The doctor may also want to measure EEG simultaneously with the MEG. In that case, electrodes are also affixed to the head. Next, the position of the coils and the electrodes are precisely measured with a special wand called a digitizer.
You will be alone in the exam room during much of the MEG procedure. At all times during your exam, the technologist will be able to see, hear and speak with you using a two-way intercom. Many MEG centers allow a friend or parent to stay in the room as long as they are also screened for safety in the magnetic environment.
The entire examination usually takes between one to two hours, depending on the extent of functional mapping. During this time they will have no special tasks to perform and can even go to sleep. Patients can be given breaks, if needed.
No matter what measurement is made with the MEG, the patient will be asked to hold relatively still during the recording and to minimize eye-movement, muscular clenching, etc.
After the MEG data collection is complete, the doctor or technician will assist the patient out of the shielded room. Electrodes and head position indicator coils will be removed. If you or your child have been sedated or anesthetized for an MEG exam, you will be sent to a recovery room where recovery time ranges from approximately 30 minutes to two hours after the exam is completed. If you have not been sedated, no recovery period is necessary. You may resume your usual activities and normal diet immediately after the exam.
An MEG Scan, is a non-invasive medical test that uses a superconducting quantum interference device (SQUID) and a computer to measure neuromagnetic activity within the brain. MEG Scans are used to help locate where seizure activity is taking place in the brain. A MEG Scan is non-invasive and does not cause any pain to the person receiving the test. Proper precautions need to be made before having a MEG Scan and the entire test can take on average one to two hours.
Boehm, N. L. (2021). Magnetic Resonance Imaging (MRI). The Defeating Epilepsy Foundation Blog. Retrieved from: https://www.defeatingepilepsy.org/medical-diagnostic-series/mri/
Burgess, R. (2023). MEG Test. Cleveland Clinic. Retrieved from: https://my.clevelandclinic.org/health/diagnostics/17218-meg-test
Radiological Society of North America (2022). Magnetoencephalography. RadiologyInfo.org. Retrieved from: https://www.radiologyinfo.org/en/info/meg