MEG System description: KIT Machine

System Overview

MagnetoEncephaloGraphy (MEG) systems are machines capable of measuring the magnetic field generated by the brain. They provide high temporal and spatial resolutions. They are non-invasive, similar to a microphone listening to your voice, MEG listens for the brain activity. MEGs are equipped with highly sensitive sensors called SQUIDs. In order for SQUIDS to operate, they need to be cooled down to -277 degres, to achieve this temperature liquid Helium is needed. Unlike MRI, MEG cannot show the anatomical structure of the brain, therefore MRI scans are combined with MEG measurements to identify the parts of the brain responsible for the measured brain activity. The magnetically shielded room is a product of Vacuumschmelze (Hanau, Germany). The shielding effect is provided by two layers of mu metal; the inner layer is 3 mm and the outer layer is 2 mm thick. Predicted shielding performance was rated to be -60 dB at 1 Hz; actual performance exceeds this prediction. The exterior dimensions of the room are 2.9 x 3.5 x 2.9 m, and the inner dimensions are 2.4 x 3.0 x 2.4 m. 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 external? noise offline, and 32 open positions, of which we currently use 8 to record stimulus triggers and the other 24 channels to record Eye Tracker data directly, auditory signals from our mixer and vocalization information from our optoacoustic fiber-optic microphone.

The system is located inside a magnetically shielded room. KIT refers to Kanazawa Institute of Technology, the manufacturer of the system.

LAB setup

Computers:

MEG Main PC: used to acquire the MEG data
stimulus1 pc: used to run the experiment
stimulus 2 pc: used to put the experiment

MEG-Channels

(This part needs to be rewritten) Channels 0 to 222: Gradiometers squids

Channels 208-223: Magnetometers for reference magnetic field (these are used to denoising and to understand the ambiant magnetic field the environment)

224: Lightsensor 1

225: Lightsensor 2

228: Microphone

229: Event marker bit 0

230: Event marker bit 1

231: Event marker bit 2

One of the channels (In the 80’s ) displays a digital signal, this is because one of the sensors are shut off and not used. Processing pipeline should include this exclusion and not process data from this channel. (channel name to be identified).

MEG-Racks

The KIT-MEG system has 7 racks

MSR: Magnetically Shielded Room

The KIT-MEG is located in an MSR built by VacuumShmelze

Contact

Name	Email	Number	Role
Hadi Zaatiti	hz3752@nyu.edu	+971 56 275 4921	Research Scientist
Osama Abdullah	osama.abdullah@nyu.edu	NA	Senior Scientist
Yoshiaki Adachi	adachi@ael.kanazawa-it.ac.jp	NA	MEG-KIT machine constructor reference

References

The following is a list of references for further understanding on MEG systems

MNE-Python: Overview and tutorials
- https://mne.tools/stable/auto_tutorials/intro/10_overview.html#sphx-glr-auto-tutorials-intro-10-overview-py
Marijn van Vliet’s “Introduction to MNE-Python”
- https://mybinder.org/v2/gh/wmvanvliet/neuroscience_tutorials/master?filepath=mne-intro%2Findex.ipynb
Processing and analysis scripts from various Nellab members/alumni
Kit2fiff and ICA examples:
Books:
- Hansen, Peter & Kringelbach, Morten & Salmelin, Riitta. (2010). MEG: An introduction to methods. 10.1093/acprof:oso/9780195307238.001.0001.