A magnetoencephalography (MEG) scan measures magnetic signals from the brain. The scan takes two to three hours, depending on how much activity is being mapped.
Magnetoencephalography (MEG) machine
Your child must be sleepy for the MEG scan to make sure it gathers the best information. If your child needs a sedative for the scan (see below), please allow up to three to four hours for your hospital visit. This allows enough time for the scan and for any medicine to wear off before your child goes home.
Why does my child need a MEG scan?
Cells in the brain give off magnetic as well as electrical signals. A MEG scan uses special electrodes attached to your child’s scalp to measure these magnetic signals and pinpoint the abnormal brain activity where your child’s seizures start.
Does the scan have any risks or side effects?
There are typically no risks or side effects from having a MEG scan.
How do I prepare my child for a MEG scan?
- Explain what will happen during the MEG in words your child understands.
- Make sure your child’s hair is freshly washed. Check for any signs of head lice and tell the nurse at the hospital if you see anything.
- Leave your child’s hair loose for the scan and remove any hair extensions.
- To help the electrodes stay in place during the test, do not use conditioner or styling products in your child's hair.
- Follow the instructions from your child’s MEG team to make sure your child is sleepy or asleep for the scan. You will be told to put your child to bed later than usual the night before the MEG and wake them up several times during the night. Even if your child is tired, do not allow them to sleep on their way to the scan.
- Give your child their medication as usual, unless your doctor tells you otherwise.
Will my child need to be sedated for a MEG scan?
Yes, some children may need a sedative (medicine to help them keep calm or help them sleep).
What happens when my child arrives for the MEG?
A technologist will check if your child can lie still comfortably in the MEG machine.
Your child will empty their clothes pockets and remove any watches, purses, jewellery and makeup. They can store these in a locker during the scan.
They will then change into a hospital gown and go into the MEG room.
The MEG technologist will then measure your child’s head and make small marks on the scalp with a washable marker or pen. They will also make small marks on your child’s nose and in front of their ears.
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They will put electrodes on your child’s nose and in front of their ears. These electrodes are connected to the MEG machine.
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The technologist will also put EEG electrodes on your child’s scalp.
What happens during a MEG scan?
When your child is ready, the technologist will place a MEG helmet on their head and your child will lie on the MEG bed.
The MEG will be turned on and the helmet will start to record your child’s brain activity. The MEG room is quiet during the scan and will also be darkened so that your child can fall asleep.
The MEG technologist will sit just outside the MEG room and monitor your child through a video camera.
Your child will have to keep their head still during the scan. Depending on the specific part of their brain where your child’s seizures start, they will do one or more of the following tests:
- somatosensory evoked fields (SEF)
- visual evoked fields (VEF)
- auditory evoked fields (AEF).
Somatosensory evoked fields (SEF) test
Your child will have this test if their seizures start in the area of the brain that controls sensation. It takes 20 to 30 minutes.
If your child’s seizures start in or near the area of the brain that controls arm sensation, your child will have a small stimulator placed on their wrist. The stimulator will receive a small electrical signal that will make your child’s thumb move or ‘dance’. In turn, this will send a message to the part of the brain that controls sensation. This stimulation is done on both wrists and takes about 20 minutes.
If your child’s seizures start in or near the area of the brain that controls leg sensation, the stimulator will be placed on your child’s inner ankle. This time, the small electrical signal will make the big toe ‘dance’. This stimulation is done on both ankles and takes about 30 minutes.
Visual evoked fields (VEF) test
Your child will have this test if their seizures start in or near the visual area of the brain (the part that controls sight). It takes about 30 minutes.
During the test, your child will look at a screen showing a moving black and white checker board pattern. They will be asked to focus on a dot in the centre of the screen while the black and white squares move. This will send a message to the part of the brain that processes what your child sees.
Auditory evoked fields (AEF) test
Your child will have this test if their seizures start in or near the auditory part of the brain (the area that controls your child’s hearing). It takes about 30 minutes.
During the test, your child will listen to beeps in one ear and white noise in the other ear while they lie still in the MEG scanner. Your child will be asked to concentrate on the sounds. This will send a message to the part of the brain that processes what your child hears. This test is done for both ears.
Doctors will study the scan so that they can find the area of your child’s brain that controls hearing.
May I stay with my child during the MEG scan?
The MEG machine is very sensitive and will pick up the brain activity of everyone in the room. As a result, your child must be in the MEG room alone. You may wait outside the MEG room and see your child on a screen.
What should I expect after a MEG scan?
Once your child completes the SEF, VEF and/or AEF test, the technologist will remove the EEG wires and electrodes. Your child will then have a few round stickers placed on top of their nose and in front of their ears, where the electrodes were placed. They will then have a short MRI scan, which will take about 10 minutes.
Once all the tests are done, the technologist will remove the stickers from your child. Your child may then get dressed and leave. If your child took a sedative, they may leave only when they are alert and fully recovered.
Your child’s hair may be a little sticky from the paste that was used to attach the electrodes to their scalp. You can easily wash it away with shampoo and water.
When will I get the test results?
Your doctor will receive the report of the MEG results and discuss them with you and your child at a follow-up appointment about four to six weeks after the scan.
If your doctor has told you that your child needs a sedative for the MEG, someone from the MEG team will contact you with instructions on when your child needs to stop eating and drinking before their appointment.
If the MEG is booked without a sedative but you think your child needs it, please contact the MEG team at 416-813-5774 and choose option 3.