Example MEG analysis
  
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The Magnetoencephalography system (MEG) was installed at the Université de Montréal in 2005. It was funded by a Canadian Fund for Innovation grant.
The unit is a 275-sensor system manufactured in Canada by CTF Ltd. It can simultaneously collect Electroencephalography (EEG) data.

Below is an introduction to the MEG;
SEE ALSO: What Is MEG?


WHAT DOES A MEG SYSTEM LOOK LIKE?
Left: Example of a MEG unit; notice the adjustable seat and projector-style presentation device (which uses a set of mirrors).
Right bottom: Photo of the MEG laboratory while it was being installed in 2005 (the white cylinder is the Dewar -- see below; the subject's head sits just inside but not touching the concave area at the bottom).
Subject in MEG MEG Cabin


HOW DOES MEG WORK?

Above: Schematic of a MEG system showing liquid Helium container, vacuum areas and the SQUID (Superconducting Quantum Interference Devices) sensors
Below: The inner compartment of the Dewar (shown during installation) is filled with helium, which super-cools the sensors so that they become superconducting and can pick up the very faint magnetic signals emanating from the brain. The vacuum is required as insulation to maintain the very low sensor temperature and to ensure that the person in the device cannot feel the cold. The signals are amplified, digitized and sent to a computer for recording.
Interior of MEG room


WHAT TECHNICAL DIFFICULTIES ARE INVOLVED IN OBTAINING ACCURATE MEG DATA?
First, because the signals are so small (1 billionth that of the earth's magnetic field), all sources of noise contamination must be dealt with. On the left, the two sensor coils are wound in opposite directions, effectively cancelling the effect of far away fields and keeping only close-by cortical magnetic fields. The entire MEG booth is shielded by a special metal cladding that is grounded (noise from electrical devices, motors, etc. is effectively blocked). Reference sensors also eliminate far sources.
Noise reduction
Head Localization
Secondly, even small movements of the subject's head must be compensated for in the data. Localization coils provide the position information needed for this.
Thirdly, ocular artefacts (blinking and eye movements) are orders of magnitude greater than the actual data. The four right columns contain a graph of the data from each of the sensors and most have a disturbance midway (the red and blue circles on the spherical view of the top of the brain at this time show that this dominates any other data. They are removed by sophisticated software.
Occular artefacts


WHAT STEPS ARE NECESSARY TO ANALYSE MEG DATA?
Here is a list of some of the procedures for MEG analysis (not necessarily in this exact order):