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A 7-channel high-Tc SQUID-based on-scalp MEG system

Journal article
Authors Christoph Pfeiffer
Silvia Ruffieux
Lars Jönsson
Maxim Chukharkin
Alexei Kalabukhov
Minshu Xie
Dag Winkler
Justin F. Schneiderman
Published in IEEE Transactions on Biomedical Engineering
Volume 67
Issue 5
Pages 1483-1489
ISSN 0018-9294
Publication year 2020
Published at Institute of Neuroscience and Physiology, Department of Clinical Neuroscience
Pages 1483-1489
Language en
Subject categories Medical Engineering, Neurosciences


Objective: To present the technical design and demonstrate the feasibility of a multi-channel on-scalp magnetoencephalography (MEG) system based on high critical temperature (high- Tc ) superconducting quantum interference devices (SQUIDs). Methods: We built a liquid nitrogen-cooled cryostat that houses seven YBCO SQUID magnetometers arranged in a dense, head-aligned array with minimal distance to the room-temperature environment for all sensors. We characterize the performance of this 7-channel system in terms of on-scalp MEG utilization and present recordings of spontaneous and evoked brain activity. Results: The center-to-center spacing between adjacent SQUIDs is 12.0 and 13.4 mm and all SQUIDs are in the range of 1-3 mm of the head surface. The cryostat reaches a base temperature of ∼ 70 K and stays cold for > 16 h with a single 0.9 L filling. The white noise levels of the magnetometers is 50–130 fT/Hz 1/2 at 10 Hz and they show low sensor-to-sensor feedback flux crosstalk ( < 0.6%). We demonstrate evoked fields from auditory stimuli and single-shot sensitivity to alpha modulation from the visual cortex. Conclusion: All seven channels in the system sensitively sample neuromagnetic fields with mm-scale scalp standoff distances. The hold time of the cryostat furthermore is sufficient for a day of recordings. As such, our multi-channel high- Tc SQUID-based system meets the demands of on-scalp MEG. Significance: The system presented here marks the first high- Tc SQUID-based on-scalp MEG system with more than two channels. It enables us to further explore the benefits of on-scalp MEG in future recordings.

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