Precision magnetic field modelling and control for wearable magnetoencephalography
Optically-pumped magnetometers (OPMs) are highly sensitive, compact magnetic field sensors, which offer a viable alternative to cryogenic sensors (superconducting quantum interference devices – SQUIDs) for magnetoencephalography (MEG). With the promise of a wearable system that offers lifespan compl...
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Format: | Article |
Language: | English |
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Elsevier
2021-11-01
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Series: | NeuroImage |
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Online Access: | http://www.sciencedirect.com/science/article/pii/S1053811921006741 |
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doaj-dec6004ccc154422869dcd2839a743a4 |
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record_format |
Article |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Molly Rea Niall Holmes Ryan M. Hill Elena Boto James Leggett Lucy J. Edwards David Woolger Eliot Dawson Vishal Shah James Osborne Richard Bowtell Matthew J. Brookes |
spellingShingle |
Molly Rea Niall Holmes Ryan M. Hill Elena Boto James Leggett Lucy J. Edwards David Woolger Eliot Dawson Vishal Shah James Osborne Richard Bowtell Matthew J. Brookes Precision magnetic field modelling and control for wearable magnetoencephalography NeuroImage Optically-pumped magnetometer OPM Magnetoencephalography MEG Magnetic field Nulling |
author_facet |
Molly Rea Niall Holmes Ryan M. Hill Elena Boto James Leggett Lucy J. Edwards David Woolger Eliot Dawson Vishal Shah James Osborne Richard Bowtell Matthew J. Brookes |
author_sort |
Molly Rea |
title |
Precision magnetic field modelling and control for wearable magnetoencephalography |
title_short |
Precision magnetic field modelling and control for wearable magnetoencephalography |
title_full |
Precision magnetic field modelling and control for wearable magnetoencephalography |
title_fullStr |
Precision magnetic field modelling and control for wearable magnetoencephalography |
title_full_unstemmed |
Precision magnetic field modelling and control for wearable magnetoencephalography |
title_sort |
precision magnetic field modelling and control for wearable magnetoencephalography |
publisher |
Elsevier |
series |
NeuroImage |
issn |
1095-9572 |
publishDate |
2021-11-01 |
description |
Optically-pumped magnetometers (OPMs) are highly sensitive, compact magnetic field sensors, which offer a viable alternative to cryogenic sensors (superconducting quantum interference devices – SQUIDs) for magnetoencephalography (MEG). With the promise of a wearable system that offers lifespan compliance, enables movement during scanning, and provides higher quality data, OPMs could drive a step change in MEG instrumentation. However, this potential can only be realised if background magnetic fields are appropriately controlled, via a combination of optimised passive magnetic screening (i.e. enclosing the system in layers of high-permeability materials), and electromagnetic coils to further null the remnant magnetic field. In this work, we show that even in an OPM-optimised passive shield with extremely low (<2 nT) remnant magnetic field, head movement generates significant artefacts in MEG data that manifest as low-frequency interference. To counter this effect we introduce a magnetic field mapping technique, in which the participant moves their head to sample the background magnetic field using a wearable sensor array; resulting data are compared to a model to derive coefficients representing three uniform magnetic field components and five magnetic field gradient components inside the passive shield. We show that this technique accurately reconstructs the magnitude of known magnetic fields. Moreover, by feeding the obtained coefficients into a bi-planar electromagnetic coil system, we were able to reduce the uniform magnetic field experienced by the array from a magnitude of 1.3±0.3 nT to 0.29±0.07 nT. Most importantly, we show that this field compensation generates a five-fold reduction in motion artefact at 0‒2 Hz, in a visual steady-state evoked response experiment using 6 Hz stimulation. We suggest that this technique could be used in future OPM-MEG experiments to improve the quality of data, especially in paradigms seeking to measure low-frequency oscillations, or in experiments where head movement is encouraged. |
topic |
Optically-pumped magnetometer OPM Magnetoencephalography MEG Magnetic field Nulling |
url |
http://www.sciencedirect.com/science/article/pii/S1053811921006741 |
work_keys_str_mv |
AT mollyrea precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT niallholmes precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT ryanmhill precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT elenaboto precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT jamesleggett precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT lucyjedwards precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT davidwoolger precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT eliotdawson precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT vishalshah precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT jamesosborne precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT richardbowtell precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography AT matthewjbrookes precisionmagneticfieldmodellingandcontrolforwearablemagnetoencephalography |
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spelling |
doaj-dec6004ccc154422869dcd2839a743a42021-09-05T04:39:31ZengElsevierNeuroImage1095-95722021-11-01241118401Precision magnetic field modelling and control for wearable magnetoencephalographyMolly Rea0Niall Holmes1Ryan M. Hill2Elena Boto3James Leggett4Lucy J. Edwards5David Woolger6Eliot Dawson7Vishal Shah8James Osborne9Richard Bowtell10Matthew J. Brookes11Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UKSir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK; Corresponding author at: Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD.Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UKSir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UKSir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UKSir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UKMagnetic Shields Limited, Headcorn Road, Staplehurst, Tonbridge, Kent, TN12 0DS, UKMagnetic Shields Limited, Headcorn Road, Staplehurst, Tonbridge, Kent, TN12 0DS, UKQuSpin Inc., 331 South 104th Street, Suite 130, Louisville, 80027, Colorado, USAQuSpin Inc., 331 South 104th Street, Suite 130, Louisville, 80027, Colorado, USASir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UKSir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UKOptically-pumped magnetometers (OPMs) are highly sensitive, compact magnetic field sensors, which offer a viable alternative to cryogenic sensors (superconducting quantum interference devices – SQUIDs) for magnetoencephalography (MEG). With the promise of a wearable system that offers lifespan compliance, enables movement during scanning, and provides higher quality data, OPMs could drive a step change in MEG instrumentation. However, this potential can only be realised if background magnetic fields are appropriately controlled, via a combination of optimised passive magnetic screening (i.e. enclosing the system in layers of high-permeability materials), and electromagnetic coils to further null the remnant magnetic field. In this work, we show that even in an OPM-optimised passive shield with extremely low (<2 nT) remnant magnetic field, head movement generates significant artefacts in MEG data that manifest as low-frequency interference. To counter this effect we introduce a magnetic field mapping technique, in which the participant moves their head to sample the background magnetic field using a wearable sensor array; resulting data are compared to a model to derive coefficients representing three uniform magnetic field components and five magnetic field gradient components inside the passive shield. We show that this technique accurately reconstructs the magnitude of known magnetic fields. Moreover, by feeding the obtained coefficients into a bi-planar electromagnetic coil system, we were able to reduce the uniform magnetic field experienced by the array from a magnitude of 1.3±0.3 nT to 0.29±0.07 nT. Most importantly, we show that this field compensation generates a five-fold reduction in motion artefact at 0‒2 Hz, in a visual steady-state evoked response experiment using 6 Hz stimulation. We suggest that this technique could be used in future OPM-MEG experiments to improve the quality of data, especially in paradigms seeking to measure low-frequency oscillations, or in experiments where head movement is encouraged.http://www.sciencedirect.com/science/article/pii/S1053811921006741Optically-pumped magnetometerOPMMagnetoencephalographyMEGMagnetic fieldNulling |