A 7-Channel High- \text SQUID-Based On-Scalp MEG System

• Published in: IEEE transactions on biomedical engineering Vol. 67; no. 5; pp. 1483 - 1489
• Main Authors: Pfeiffer, Christoph, Ruffieux, Silvia, Jonsson, Lars, Chukharkin, Maxim L., Kalaboukhov, Alexei, Xie, Minshu, Winkler, Dag, Schneiderman, Justin F.
• Format: Journal Article
• Language: English
• Published: IEEE 01.05.2020
• Subjects: Crosstalk; high-<named-content xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" content-type="math" xlink:type="simple"> <inline-formula> <tex-math notation="LaTeX"> {T}_\text{c}</tex-math> </inline-formula> </named-content> SQUID; Magnetic heads; Magnetic sensors; Magnetoencephalography (MEG); Magnetometers; multichannel system; on-scalp MEG; SQUIDs; Temperature sensors
• ISSN: 0018-9294; 1558-2531
• DOI: 10.1109/TBME.2019.2938688

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-<inline-formula><tex-math notation="LaTeX">{T}_\text{c}</tex-math></inline-formula>) 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 <inline-formula><tex-math notation="LaTeX">\sim</tex-math></inline-formula>70 K and stays cold for <inline-formula><tex-math notation="LaTeX">></tex-math></inline-formula>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 (<inline-formula><tex-math notation="LaTeX">< </tex-math></inline-formula>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-<inline-formula><tex-math notation="LaTeX">{T}_\text{c}</tex-math></inline-formula> SQUID-based system meets the demands of on-scalp MEG. Significance: The system presented here marks the first high-<inline-formula><tex-math notation="LaTeX">{T}_\text{c}</tex-math></inline-formula> 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.