Open AccessTheoretical advantages of a triaxial optically pumped magnetometer magnetoencephalography system
Author(s) -
Matthew J. Brookes,
Elena Boto,
Molly Rea,
Vishal Shah,
James Osborne,
Niall Holmes,
Ryan M. Hill,
James Leggett,
Natalie Rhodes,
Richard Bowtell
Publication year - 2021
Publication title -
neuroimage
Language(s) - English
Resource type - Journals
eISSN - 1095-9572
pISSN - 1053-8119
DOI - 10.1016/j.neuroimage.2021.118025
Subject(s) - magnetoencephalography , magnetometer , computer science , detector , biomagnetism , interference (communication) , instrumentation (computer programming) , magnetic field , electronic engineering , orientation (vector space) , acoustics , physics , engineering , telecommunications , psychology , channel (broadcasting) , geometry , mathematics , electroencephalography , quantum mechanics , psychiatry , operating system
The optically pumped magnetometer (OPM) is a viable means to detect magnetic fields generated by human brain activity. Compared to conventional detectors (superconducting quantum interference devices) OPMs are small, lightweight, flexible, and operate without cryogenics. This has led to a step change in instrumentation for magnetoencephalography (MEG), enabling a "wearable" scanner platform, adaptable to fit any head size, able to acquire data whilst subjects move, and offering improved data quality. Although many studies have shown the efficacy of 'OPM-MEG', one relatively untapped advantage relates to improved array design. Specifically, OPMs enable the simultaneous measurement of magnetic field components along multiple axes (distinct from a single radial orientation, as used in most conventional MEG systems). This enables characterisation of the magnetic field vector at all sensors, affording extra information which has the potential to improve source reconstruction. Here, we conduct a theoretical analysis of the critical parameters that should be optimised for effective source reconstruction. We show that these parameters can be optimised by judicious array design incorporating triaxial MEG measurements. Using simulations, we demonstrate how a triaxial array offers a dramatic improvement on our ability to differentiate real brain activity from sources of magnetic interference (external to the brain). Further, a triaxial system is shown to offer a marked improvement in the elimination of artefact caused by head movement. Theoretical results are supplemented by an experimental recording demonstrating improved interference reduction. These findings offer new insights into how future OPM-MEG arrays can be designed with improved performance.