Magnetoencephalography, or MEG scan, is an imaging technique that identifies brain activity and measures small magnetic fields produced in the brain. The scan is used to produce a magnetic source image (MSI) to pinpoint the source of seizures.

Magnetic fields are detected by extremely sensitive devices called "super conducting detectors and amplifiers," also known as SQUIDs.

The scanner, used to detect and amplify magnetic signals produced by the brain, doesn't emit radiation or magnetic fields.

Preparing for the Test

We may ask that your child arrive sleep deprived or tired in hopes of recording his or her brain activity in the awake, drowsy and sleep states. Your child can eat normally before the scan and should take medications as usual.

Because metals can interfere with the scan, your child should not wear any clothing with metal zippers or snaps above the waist and shouldn't wear jewelry or a wrist watch. Electronic items with a magnetic strip, also aren't allowed.

If you remain with your child during the test, you also must remove all metal and electronic items.

Please notify the MEG department in advance if your child wears braces or a permanent retainer, or has an electronic implant, such as a pacemaker or a vagus nerve stimulator.

The Scan

The test takes about two hours and is performed in the Biomagnetic Imaging Laboratory in a specially shielded room, equipped with video and intercom systems so a technician can see, hear and communicate with your child at all times.

Electrodes will be placed on your child's scalp, using paste that is water soluble. Your child will lie on a MEG bed with his or her head resting on a helmet-like MEG scanner.

What to Expect

This test causes no discomfortThe test causes no discomfort. When the scanner is on, it makes no noise.

During the scan, your child's head must be kept still. A technician will immobilize your child's head by placing sponges on both sides.

While keeping the head still, your child may be asked to move parts of his or her body or to feel, listen, look at or read to create brain activity.

An electroencephalogram (EEG) also will be performed.

Test Results

The MEG scan can provide valuable information used by doctors to locate your child's seizure focus and determine if he or she is a candidate for seizure surgery. Results from the MEG test are matched up with a magnetic resonance image (MRI), which is an anatomical picture of the brain.

The MEG and MRI create a "map," or magnetic source image (MSI), that shows areas of normal and abnormal activity in the brain.

More Information

To contact the Biomagnetic Imaging Laboratory in Radiology, call (415) 476-6888.