A new generation of magnetoencephalography: Room temperature measurements using optically-pumped magnetometers

Abstract

Advances in the field of quantum sensing mean that magnetic field sensors, operating at room temperature, are now able to achieve sensitivity similar to that of cryogenically cooled devices (SQUIDs). This means that room temperature magnetoencephalography (MEG), with a greatly increased flexibility of sensor placement can now be considered. Further, these new sensors can be placed directly on the scalp surface giving, theoretically, a large increase in the magnitude of the measured signal. Here, we present recordings made using a single optically-pumped magnetometer (OPM) in combination with a 3D-printed head-cast designed to accurately locate and orient the sensor relative to brain anatomy. Since our OPM is configured as a magnetometer it is highly sensitive to environmental interference. However, we show that this problem can be ameliorated via the use of simultaneous reference sensor recordings. Using median nerve stimulation, we show that the OPM can detect both evoked (phase-locked) and induced (non-phase-locked oscillatory) changes when placed over sensory cortex, with signals ~4 times larger than equivalent SQUID measurements. Using source modelling, we show that our system allows localisation of the evoked response to somatosensory cortex. Further, source-space modelling shows that, with 13 sequential OPM measurements, source-space signal-to-noise ratio (SNR) is comparable to that from a 271-channel SQUID system. Our results highlight the opportunity presented by OPMs to generate uncooled, potentially low-cost, high SNR MEG systems.

Using optically pumped magnetometers to measure magnetoencephalographic signals in the human cerebellum

“…This system potentially also reduces the sensor‐to‐brain distance to enhance signal magnitude (Boto et al . ). These sensors can be positioned in a dense array over a specific brain region of interest (Tierney et al .…”

“…The OP‐MEG system has been previously described in detail (Boto et al . , ; Holmes et al . ; Tierney et al .…”

Chip-scale atomic devices

“…Highresolution measurements of both heart 234-236 and brain 237 magnetic fields have been demonstrated over the last 20 years and atomic magnetometers are gaining acceptance within the biomagnetics community as a noteworthy alternative to cryogenically cooled SQUIDS. 238,239 Measurements of magnetic fields produced by the heart have been carried out with chip-scale atomic magnetometers 217,240 and have been confirmed with nearsimultaneous SQUID-based measurements. The somewhat worse sensitivity of these early chip-scale atomic magnetometers was partially offset by an increase in the detected signal due to the proximity of the chip-scale magnetometers to the sources, as compared with the SQUIDS, which require considerable thermal shielding to function in a roomtemperature environment.…”

Reproducibility ofEEG‐MEGfusion source analysis of interictal spikes: Relevance in presurgical evaluation of epilepsy

“…We have explored the sub‐sampling of EEG electrodes according to the standard montages such as 10–20 or 10‐10 system. Furthermore, exploring the fusion of 54 electrodes EEG system with few MEG sensors (25 MEG sensors) was interesting considering the advent of the next generation of non‐SQUID‐based individual MEG sensors (Boto et al, ; Öisjöen et al, ). These results indicate that by combining even only few EEG or few MEG sensors, to a complete MEG or EEG setup, we can achieve a good spatial sampling of the head while bringing complementary information from both EEG and MEG to ensure accurate fusion.…”