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Cited by 269Atomic and Subatomic Physics ResearchMagnetic Field Sensors TechniquesAdvanced MRI Techniques and Applications

On-scalp MEG system utilizing an actively shielded array of optically-pumped magnetometers

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Iivanainen, Joonas, Zetter, Rasmus, Grön, Mikael, Hakkarainen, Karoliina, Parkkonen, Lauri·2019·NeuroImage
DOI 10.1016/j.neuroimage.2019.03.022PMC PMC6536327

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Abstract

The spatial resolution of magnetoencephalography (MEG) can be increased from that of conventional SQUID-based systems by employing on-scalp sensor arrays of e.g. optically-pumped magnetometers (OPMs). However, OPMs reach sufficient sensitivity for neuromagnetic measurements only when operated in a very low absolute magnetic field of few nanoteslas or less, usually not reached in a typical magnetically shielded room constructed for SQUID-based MEG. Moreover, field drifts affect the calibration of OPMs. Static and dynamic suppression of interfering fields is thus necessary for good-quality neuromagnetic measurements with OPMs. Here, we describe an on-scalp MEG system that utilizes OPMs and external compensation coils that provide static and dynamic shielding against ambient fields. In a conventional two-layer magnetically shielded room, our coil system reduced the maximum remanent DC-field component within an 8-channel OPM array from 70 to less than 1 nT, enabling the sensors to operate in the sensitive spin exchange relaxation-free regime. When compensating field drifts below 4 Hz, a low-frequency shielding factor of 22 dB was achieved, which reduced the peak-to-peak drift from 1.3 to 0.4 nT and thereby the standard deviation of the sensor calibration from 1.7% to 0.5%. Without band-limiting the field that was compensated, a low-frequency shielding factor of 43 dB was achieved. We validated the system by measuring brain responses to electric stimulation of the median nerve. With dynamic shielding and digital interference suppression methods, single-trial somatosensory evoked responses could be detected. Our results advance the deployment of OPM-based on-scalp MEG in lighter magnetic shields.

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  • OPM-MEG experiments involving participant motion require an OPM-optimised MSR with a very low remnant magnetic field and active magnetic shielding.

    “These constraints mean that OPM-MEG experiments involving participant motion require an OPM-optimised MSR with a very low remnant magnetic field along with ‘active’ magnetic shielding”

    From Naturalistic Hyperscanning with Wearable Magnetoencephalography (2023) · cites this paper as [35]

    The Introduction says that head motion through a remanent field changes the field experienced by wearable OPM sensors, and that nulling the field reduces those changes. But the Abstract and Discussion describe operation in a conventional two-layer MSR using external compensation coils, not a requirement for an OPM-optimised MSR. The paper demonstrates benefits of active shielding for field drifts; it does not establish that active shielding is required for every experiment involving participant motion. (LLM, conf=0.86)

    Experimental — accuracy not yet measured

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Cited by

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Authors
Iivanainen, J., Zetter, R., Grön, M., Hakkarainen, K., & Parkkonen, L.
Affiliations
Aalto University (FI)
Corresponding author
Iivanainen, Joonas
ORCID
Venue
NeuroImage
Publisher
Elsevier BV
Published
2019-07
Volume
194
Pages
244-258
ISSN
1053-8119 (ISSN-L)
DOI
10.1016/j.neuroimage.2019.03.022
PMC
PMC6536327
OpenAlex
W2952338767
Cited by
269
References
2
Citations by year
2026: 29 · 2025: 52 · 2024: 37 · 2023: 47 · 2022: 38 · 2021: 34 · 2020: 19 · 2019: 13
FWCI
11.43
Type
journal article
Language
en
Open access
Licence
Locations
  • NeuroImage (publishedVersion, cc-by-nc-nd)
  • bioRxiv (Cold Spring Harbor Laboratory) (acceptedVersion, cc-by-nc-nd)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion, cc-by-nc-nd)
  • Aaltodoc (Aalto University) (submittedVersion, cc-by-nc-nd)
Funders
  • Finnish Cultural Foundation (00170330, 00180388)
  • European Research Council under ERC (678578)
  • National Institute of Neurological Disorders and Stroke of the National Institutes of Health (R01NS094604)
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Atomic and Subatomic Physics Research
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Magnetic Field Sensors Techniques
  • Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Advanced MRI Techniques and Applications
Keywords
optically pumped magnetometers, magnetic shielding, compensation coils, sensor calibration, somatosensory evoked potentials, median nerve stimulation
MeSH terms
Humans, Scalp, Magnetoencephalography, Neuroimaging

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