Magnetoencephalography (MEG) or Magnetic Source Imaging (MSI)

Magnetoencephalography (MEG), also known as Magnetic Source Imaging (MSI), is a non-invasive scanning technique that provides information about the structure and function of the brain. It is a safe and painless procedure.

How does it work?

MEG detects small biomagnetic signals that the brain produces and records magnetic fields over the surface of the head. These signals show which areas of the brain are active, allowing us to see how different areas of the brain interact with one another.

MEG can help identify the areas of the brain emitting abnormal electric currents that cause seizures. Patients often perform cognitive tasks during the MEG to help localize the learning and memory areas of the brain. The MEG produces a high-resolution image of the brain that relates to the functioning of the brain with behaviour.

One advantage MEG has over PET and fMRI, which depend on changes in blood flow in the brain, is speed. Unlike PET and fMRI, MEG is fast enough to provide information about the changes in neuronal firing to the millisecond. MEG records magnetic signals produced by the responding neurons, which enables us to see rapid brain potentials.

Before an MEG/MSI

  • No special diet is required. You can eat and drink as usual.
  • Dress in comfortable clothing on the day of the test.
  • Wash your hair and refrain from using hairspray, gel or other hair products.
  • Do not wear any metal objects (jewellery, piercings, belts, etc.).

During an MEG/MSI

  • The test will take place in a shielded room away from fan motors, elevators and other sources of magnetic “noise.”
  • You will either lie down on a bed or sit in a chair.
  • An electrical device, known as a neuromagnetometer, will be placed near your head. This instrument acts as an antenna to pick up the magnetic fields emerging from the brain. It takes a snapshot every millisecond.


This test is covered by the Ontario Health Insurance Plan (OHIP).

Click here to learn about other types of diagnostic tests.