Wearable magnetoencephalography in a lightly shielded environment

Holmes, Niall; Leggett, James; Hill, Ryan M.; Rier, Lukas; Boto, Elena; Schofield, Holly; Hayward, Tyler; Dawson, Eliot; Woolger, David; Shah, Vishal; Taulu, Samu; Brookes, Matthew J.; Bowtell, Richard

Abstract

Wearable magnetoencephalography based on optically pumped magnetometers (OPM-MEG) offers non-invasive and high-fidelity measurement of human brain electrophysiology. The flexibility of OPM-MEG also means it can be deployed in participants of all ages and permits scanning during movement. However, the magnetic fields generated by neuronal currents – which form the basis of the OPM-MEG signal – are much smaller than environmental fields, and this means measurements are highly sensitive to interference. Further, OPMs have a low dynamic range, and should be operated in near-zero background field. Scanners must therefore be housed in specialised magnetically shielded rooms (MSRs), formed from multiple layers of shielding material. The MSR is a critical component, and current OPM-optimised shields are large (>3 m in height), heavy (>10,000 kg) and expensive (with up to 5 layers of material). This restricts the uptake of OPM-MEG technology. Here, we show that the application of the Maxwell filtering techniques signal space separation (SSS) and its spatiotemporal extension (tSSS) to OPM-MEG data can isolate small signals of interest measured in the presence of large interference. We compare phantom recordings and MEG data from a participant performing a motor task in a state-of-the-art 5-layer MSR, to similar data collected in a lightly shielded room: application of tSSS to data recorded in the lightly shielded room allowed accurate localisation of a dipole source in the phantom and neuronal sources in the brain. Our results point to future deployment of OPM-MEG in lighter, cheaper and easier-to-site MSRs which could catalyse widespread adoption of the technology.

Citation

Holmes, N., Leggett, J., Hill, R. M., Rier, L., Boto, E., Schofield, H., Hayward, T., Dawson, E., Woolger, D., Shah, V., Taulu, S., Brookes, M. J., & Bowtell, R. (2025). Wearable magnetoencephalography in a lightly shielded environment. IEEE Transactions on Biomedical Engineering, 72(2), 609-618. https://doi.org/10.1109/tbme.2024.3465654

• Journal Article Type: Article
• Acceptance Date: Sep 20, 2024
• Online Publication Date: Sep 20, 2024
• Publication Date: 2025-02
• Deposit Date: Feb 3, 2025
• Publicly Available Date: Feb 7, 2025
• Journal: IEEE Transactions on Biomedical Engineering
• Electronic ISSN: 1558-2531
• Publisher: Institute of Electrical and Electronics Engineers
• Peer Reviewed: Peer Reviewed
• Volume: 72
• Issue: 2
• Pages: 609-618
• DOI: https://doi.org/10.1109/tbme.2024.3465654
• Public URL: https://nottingham-repository.worktribe.com/output/40544450
• Publisher URL: https://ieeexplore.ieee.org/document/10685146