Magnetoencephalography With Optically Pumped⁴He Magnetometers at Ambient Temperature

Abstract

In this paper, we present the first proof of concept confirming the possibility to record magnetoencephalographic (MEG) signals with Optically Pumped Magnetometers (OPMs) based on the parametric resonance of 4He atoms. The main advantage of this kind of OPM is the possibility to provide a tri-axis vector measurement of the magnetic field at room-temperature (the 4He vapor is neither cooled nor heated). The sensor achieves a sensitivity of 210 fT/√Hz in the bandwidth [2 Hz - 300 Hz]. MEG simulation studies with a brain phantom were cross-validated with real MEG measurements on a healthy subject. For both studies, MEG signal was recorded consecutively with OPMs and Superconducting Quantum Interference Devices (SQUIDs) used as reference sensors. For healthy subject MEG recordings, three MEG proofs of concept were carried out: auditory and visual evoked fields (AEF, VEF), and spontaneous activity. M100 peaks have been detected on evoked responses recorded by both OPMs and SQUIDs with no significant difference in latency. Concerning spontaneous activity, an attenuation of the signal power between 8-12 Hz (alpha band) related to eyes opening has been observed with OPM similarly to SQUID. All these results confirm that the room temperature vector 4He OPMs can record MEG signals and provide reliable information on brain activity.

Optically pumped magnetometers disclose magnetic field components of the muscular action potential

“…The magnetic fields generated by the MAP are in the range of 0.01 to 0.1 nanotesla (nT), and therefore, special devices are required to record these small magnetic fields. OPMs are newly developed sensors (Mhaskar et al, 2012;Colombo et al, 2016;Labyt et al, 2019) 4 that can measure these small magnetic fields. Unlike SQUIDs (Reincke, 1993), OPMs are much smaller and can be placed in close proximity to the muscle.…”

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

“…These optically pumped magnetometers, working in a spin-exchange relaxation free regime are the best candidates to replace SQUID magnetometry. It is shown, that in some cases they have benefits in sensitivity, spatial resolution and cost-effectivity compared with SQUID-based magnetometers [135][136][137][138] currently used for monitoring magnetic signals from the brain, even though such magnetometers still require a magnetically shielded environment. Nowadays, only spin-exchange relaxation free variants have been used for magnetoencephalography [28,139,140].…”

Overview of Magnetoencephalography—Brief History of its Sensors and Hardware

“…Many articles on MEG using optically pumped magnetic sensors have already been published [45][46][47][48][49][50][51][52][53], but the most well known system was reported by Boto et al [49] in 2018, which is a MEG allowing head movement . The system comprises 13 optically pumped magnetic sensors (QuSpin) with sensitivity of 15 fT/ Hz which are mounted on the scalp surface, and a magnetic shield made of material with high magnetic permeability combined with a 3-axis multi-layered active shield, which creates a uniform magnetic eld space (within this space, the error of uniformity of the eld is within 5%) of 40 cm 3 around the head of the subject wearing the sensors.…”