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Magnetic Field Mapping and Correction for Moving OP-MEG

Mellor, Stephanie; Tierney, Tim M.; O'Neill, George C.; Alexander, Nicholas; Seymour, Robert A.; Holmes, Niall; Lopez, Jose D.; Hill, Ryan M.; Boto, Elena; Rea, Molly; Roberts, Gillian; Leggett, James; Bowtell, Richard; Brookes, Matthew J.; Maguire, Eleanor A.; Walker, Matthew C.; Barnes, Gareth R.

Magnetic Field Mapping and Correction for Moving OP-MEG Thumbnail


Stephanie Mellor

Tim M. Tierney

George C. O'Neill

Nicholas Alexander

Robert A. Seymour

Mansfield Research Fellow

Jose D. Lopez

Molly Rea

Gillian Roberts

Technical Specialist - Opm Meg

Eleanor A. Maguire

Matthew C. Walker

Gareth R. Barnes


Background: Optically pumped magnetometers (OPMs) have made moving, wearable magnetoencephalography (MEG) possible. The OPMs typically used for MEG require a low background magnetic field to operate, which is achieved using both passive and active magnetic shielding. However, the background magnetic field is never truly zero Tesla, and so the field at each of the OPMs changes as the participant moves. This leads to position and orientation dependent changes in the measurements, which manifest as low frequency artefacts in MEG data. Objective: We model the spatial variation in the magnetic field and use the model to predict the movement artefact found in a dataset. Methods: We demonstrate a method for modelling this field with a triaxial magnetometer, then show that we can use the same technique to predict the movement artefact in a real OPM-based MEG (OP-MEG) dataset. Results: Using an 86-channel OP-MEG system, we found that this modelling method maximally reduced the power spectral density of the data by 27.8 ± 0.6 dB at 0 Hz, when applied over 5 s non-overlapping windows. Conclusion: The magnetic field inside our state-of-the art magnetically shielded room can be well described by low-order spherical harmonic functions. We achieved a large reduction in movement noise when we applied this model to OP-MEG data. Significance: Real-time implementation of this method could reduce passive shielding requirements for OP-MEG recording and allow the measurement of low-frequency brain activity during natural participant movement.


Mellor, S., Tierney, T. M., O'Neill, G. C., Alexander, N., Seymour, R. A., Holmes, N., …Barnes, G. R. (2022). Magnetic Field Mapping and Correction for Moving OP-MEG. IEEE Transactions on Biomedical Engineering, 69(2), 528-536.

Journal Article Type Article
Acceptance Date Jul 7, 2021
Online Publication Date Jul 29, 2021
Publication Date Feb 1, 2022
Deposit Date Mar 21, 2022
Publicly Available Date Mar 21, 2022
Journal IEEE Transactions on Biomedical Engineering
Print ISSN 0018-9294
Electronic ISSN 1558-2531
Publisher Institute of Electrical and Electronics Engineers
Peer Reviewed Peer Reviewed
Volume 69
Issue 2
Pages 528-536
Public URL
Publisher URL
Additional Information © 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted
component of this work in other works.


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