Preparing for a MEG Scan
Magnetoencephalography (MEG) reveals which areas are involved in the control of a movement and how their activity is locked to the speed of the movement.
Because MEG detects the tiny magnetic fields from the brain, you will need to follow a few steps to ensure quality of the exam and optimal results:
- Remove all metal and jewelry before a MEG scan because these items will affect the quality of MEG recordings and subsequent analysis. Please tell your referring physician if you have metal medical or dental devices such as a pacemaker, patient-controlled analgesia (PCA) pump, vagus nerve stimulator, programmable ventriculoperitoneal shunt (VP) shunt, cochlear implant or braces. In addition, MEG technologists may need to evaluate certain implants (e.g., pins, clamps, clips, screws, coils shrapnel and cochlear implants) for metal content before the scan can be done.
- You will wear a hospital gown for the MEG scan. A locker will be provided to store all personal items.
- Women must wash their hair the day before the MEG scan. On the day of the scan, they must not use hairspray or wear makeup, which may contain traces of metal that can interfere with the scan.
- You must not have an MRI scan within one month prior to a MEG exam. An MRI can magnetize various body parts and alter the results of the test.
- If you have older dental fillings, we can demagnetize them before the MEG session with a degausser, a device that eliminates unwanted magnetic fields.
- Similar to other imaging procedures, it’s important to hold your head still during the recording of MEG data.
During a MEG Scan
MEG recordings are done in special shielded room that blocks magnetic fields in the environment. This ensures that only the magnetic fields generated by the brain are detected by the MEG sensors.
After entering the MEG room, you may either be asked to lie on a table bed or sit in a comfortable armchair. A special helmet containing the MEG sensors will be placed around your head. This special helmet will not cover your face, so you may even be able to watch a video and listen to music during the test. You will be asked not to move during the test, which runs for about one hour, with several short breaks. There is no loud noise during the test; the MEG environment is quiet and the recording is totally non-invasive.
To help identify the regions of the brain controlling movement and other important functions, various stimuli may be used during the MEG exam. These stimuli vary depending on the brain system that might be of interest to the patient’s condition. For epilepsy, a patient may simply rest in the scanner and watch a movie or listen to music. For pre-surgical evaluation of brain tumors, the stimuli would focus on exploring the brain function as close as possible to the surgical target. This might concern language, memory, movements and various sensory systems (e.g., vision and touch). Stimuli may include sounds, a series of pictures, movies, tiny air puffs or very mild electrical stimulation.
Very often, an EEG recording will be done at the same time the MEG scan is performed.
If you have not had an MRI scan, which shows the brain’s structure, this will be done after the MEG session. This is needed so the MEG results can be combined with the MRI for a full picture and brain activations and structures. The combined scan — called magnetic source imaging — gives neurosurgeons a detailed “map” of damaged and healthy brain tissue to help plan surgery.
Trained MEG technologists ensure that MEG recordings provide the optimal quality of data. They work in coordination with the MEG physicists to provide in-depth analysis of the MEG recordings, possibly in conjunction with the anatomical information obtained from MRI. After several days, a detailed report is subsequently provided to the patient’s physician.