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Updated: Jan 27, 2026
06:04
Functional Mapping with Simultaneous MEG and EEG
Published on: June 14, 2010
18.4K
On-scalp MEG system utilizing an actively shielded array of optically-pumped magnetometers
Joonas Iivanainen1, Rasmus Zetter1, Mikael Grön1
1Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, FI-00076, Aalto, Finland.
Neuroimage
|March 20, 2019
Summary
Optically-pumped magnetometers (OPMs) enhance magnetoencephalography (MEG) spatial resolution. This study introduces an on-scalp MEG system with coils for magnetic field suppression, enabling OPMs to function in low fields and detect brain activity.
Area of Science:
- Biophysics
- Neuroscience
- Biomedical Engineering
Background:
- Conventional SQUID-based magnetoencephalography (MEG) has limitations in spatial resolution.
- On-scalp sensor arrays using optically-pumped magnetometers (OPMs) offer improved spatial resolution.
- OPMs require operation in very low magnetic fields (nanotesla range), often unachievable in standard magnetically shielded rooms.
Purpose of the Study:
- To develop and validate an on-scalp MEG system utilizing OPMs with external compensation coils.
- To demonstrate static and dynamic magnetic field suppression for OPM-based neuromagnetic measurements.
- To enable OPM-based on-scalp MEG in less stringent magnetic shielding environments.
Main Methods:
- Implementation of an on-scalp MEG system with an 8-channel OPM array.
- Integration of external compensation coils for static and dynamic magnetic field suppression.
- Measurement of brain responses to median nerve stimulation to validate system performance.
Main Results:
- Reduced remanent DC-field from 70 nT to <1 nT, enabling OPMs to operate in the spin exchange relaxation-free regime.
- Achieved a low-frequency magnetic field shielding factor of 22 dB (up to 43 dB without band-limiting), reducing field drift and improving sensor calibration stability.
- Successfully detected single-trial somatosensory evoked responses using dynamic shielding and digital interference suppression.
Conclusions:
- The developed coil system effectively suppresses ambient magnetic fields, crucial for OPM sensitivity.
- The system enables high-quality neuromagnetic measurements with OPMs in conventional magnetic shields.
- This advancement facilitates the broader deployment of OPM-based on-scalp MEG systems.
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