Our System

The MEG system was provided by the Kanazawa Institute of Technology (Tokyo, Japan) as part of a collaboration with its Applied Electronics Laboratory. The same system is also developed and marketed by Yokogawa Electric Corporation (Yokogawa, Japan) as the MEG Vision. It is a recumbent system, with the dewar fixed in position. We refer to our system as having 160 channels, but in actuality it contains:

• 157 axial gradiometers used to measure brain activity
• 3 orthogonally-oriented (reference) magnetometers located in the dewar but away from the brain area, used to measure and reduce extramural noise offline
• 32 open positions, of which we currently use 8 to record stimulus triggers

The MEG or SQUID (Superconducting Quantum Interference Device) sensors must be kept at superconducting temperatures in order for the system to operate. To achieve this end, the dewar requires ~100L of liquid helium per week.

Data from the MEG system and other equipment is acquired by a DAQ system assembled by Eagle Technology. The system has six DAQ PCs and one control PC. Each signal is digitized with 16-bit resolution. For raw data recording we use a sampling rate of 1 kHz. We can record with a higher sampling rate but the length of acquisition time that the machine is capable of is greatly reduced as the sampling rate increases. All inputs of the 192 channels can be displayed simultaneously by the six CRT monitors. The control PC runs Windows XP.