MEG

MEG (magnetoencephalography) is a useful technology that is gaining more popularity every year. In this article, we give an overview of the different components found in all MEG systems. We also look at the different MEG systems available and give a brief breakdown of how each work.

Basic Components of a MEG

Facility – To run a MEG you need a decent sized facility to include a reading room, prep area, acquisition area, a digitizing area, an MSR (magnetically shielded room) and a utility/electronics area. Below are some examples from the MEGs in Pittsburgh, PA and Phoenix, AZ.

Prep Area – This area is dedicated to setting up your patient for a MEG study. The MEG technologist will attach HPI (head position indicator) coils and electrodes for simultaneous EEG, as well as ECG leads.

Acquisition Area – Usually located just outside the MSR, this area is where you will run the MEG. There will be one computer for acquiring MEG and EEG data and also a computer to deliver stimuli for cases when evoked responses are requested.

Digitizing Area – You will need an area free of metal (including a non-metallic chair or bed) to digitize your patient/subject. The process of digitizing allows you to locate the HPI coils, the EEG electrodes and the shape of the patient’s head. These data are used to co-register MEG source space to an MRI where the activity you are interested in can be localized in the brain.

Magnetically Shielded Room (MSR) – The signals that you are trying to record from the brain are extremely small magnetic fields. It helps to block the environmental magnetic fields (powerline, PCs moving metal carts) during the MEG recording by using a magnetically shielded room to keep out as much magnetic contamination as possible.

Electronics/Utility Area – Here is where the bulk of the electronics are housed; everything from circuit boards to fuse boxes. This area could also be where the compressor is located that powers the door to the MSR to seal it shut when running a patient/subject. Also, a helium recycler could be located here.

MEG Dewar, Helmet and SQUIDS – Each MEG has a dewar for holding liquid helium (with the exception of the York MEG). MEG is a superconducting technology and needs the extremely cold environment that liquid helium (4K or –270 °C) can provide. The helmet is where all of the sensors are located. These sensors are called “SQUIDs” (Superconducting Quantum Interference Devices). There are 3 different types of MEG SQUID sensors which are Magnetometers, Axial Gradiometers, and Planar Gradiometers.

MEGs and Their Companies

4D Neuroimaging/BTI/SHE – 4D Neuroimaging, formerly known as Biomagnetic Technologies Inc., and originally known as the S.H.E. company, was founded in 1970. The company was headquartered in San Diego, California. The company went out of business in 2009. There are still a few in service today. These systems have 148 or 248 channels and are either magnetometers or gradiometers.

RICOH MEGvision

The MEGvision was released in 1998 by Yokogawa, based in Japan. This system uses 160 coaxial gradiometers originally designed by Kanazawa Institute of Technology (KIT). RICOH purchased Yokogawa MEG in 2016. See link

CTF

CTF is a Canadian company founded in 2007. The original company was founded in the late 1980s and went out of business around 2006.  The new CTF company emerged and bought the 4D-Neuroimaging and the original CTF’s intellectual property rights. Their current MEG system will provide 275 Axial Gradiometers. See link

Compumedics – Orion

The Orion is still in development (first one will be located in Phoenix, AZ).  This unique MEG system will have two helmets of different sizes; one to fit adults and the other to fit a child’s head. The adult helmet uses 192 gradiometers while the children’s helmet will have 144 gradiometers. See link

Neuromag Oy/–Elekta – Vecotrview, Triux

Neuromag Oy founded in Helsinki Finland originally built the Neuromag Vector view system with 306 sensors, which uses 102 Magnetometers and 204 Planar Gradiometers. For a brief time they merged with BTI, then were sold to Elekta.  See link

Elekta recently sold its MEG business (”MEGIN”) to York Instruments in 2018. See link

York MEGSCAN 

York is based out of the UK. The system is still in development (first one will be located in Texas) but uses 320 Axial Gradiometers plus 32 references. One of the unique properties of this system is that it does not use liquid helium for cooling its sensors. See link

This article was written by  Shawn Walls, MA, CMEG and Susan Bowyer, Ph.D.