On-scalp magnetocorticography with optically pumped magnetometers: Simulated performance in resolving simultaneous sources

Nugent, Allison C.; Benitez-Andonegui, Amaia; Holroyd, Tom; Robinson, Stephen E.

doi:10.1016/j.ynirp.2022.100093

Cited by 19 publications

(20 citation statements)

References 48 publications

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“…This should translate to improved spatial resolution [16]. In support of this, recent simulation work [17] showed that a densely packed OPM array over a patch of cortex can localise electrophysiological brain responses at unprecedented resolution for a noninvasive device (a process the authors term 'magnetocorticography'). However, careful system calibration was a significant factor.…”

Section: Box 1 Opm Physicsmentioning

confidence: 92%

Magnetoencephalography with optically pumped magnetometers (OPM-MEG): the next generation of functional neuroimaging

Brookes

Leggett

Rea

et al. 2022

Trends in Neurosciences

180

100

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Section: Box 1 Opm Physicsmentioning

confidence: 92%

Magnetoencephalography with optically pumped magnetometers (OPM-MEG): the next generation of functional neuroimaging

Brookes

Leggett

Rea

et al. 2022

Trends in Neurosciences

180

100

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“…However, even at 3 nT, we estimate that if a 90° rotation of the head (hence a 90° rotation of the OPMs) was carried out, some sensors would experience a gain change of ∼3.8%. Such changes are known to affect the quality of MEG reconstruction 13 . However, following nulling, the background field was reduced to 0.2 nT meaning an equivalent 90° rotation would generate only a 0.018% gain change.…”

Section: Discussionmentioning

confidence: 99%

“…The result is a more practical scanner that is free from cryogenics and can, in principle, adapt to different head sizes and shapes, enabling free movement during scanning 5–9 . Since less thermal insulation is required between the sensor and the head, the OPMs are positioned closer to the brain (compared to conventional SQUID‐based systems), thereby improving sensitivity and spatial precision 10–13 . The potential of OPM‐MEG as a high‐performance functional imaging modality is significant, and growing enthusiasm within the neuroscientific and clinical research communities has been seen in recent years.…”

Section: Introductionmentioning

confidence: 99%

“… 5 , 6 , 7 , 8 , 9 Since less thermal insulation is required between the sensor and the head, the OPMs are positioned closer to the brain (compared to conventional SQUID‐based systems), thereby improving sensitivity and spatial precision. 10 , 11 , 12 , 13 The potential of OPM‐MEG as a high‐performance functional imaging modality is significant, and growing enthusiasm within the neuroscientific and clinical research communities has been seen in recent years. However, OPM‐MEG is a nascent technology, and there are significant challenges to the successful implementation of an optimized system, including control of background magnetic fields, the design of OPMs, and implementation of sensor arrays.…”

Section: Introductionmentioning

confidence: 99%

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A 90‐channel triaxial magnetoencephalography system using optically pumped magnetometers

Rea

Boto

Holmes

et al. 2022

Annals of the New York Academy of Sciences

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Magnetoencephalography (MEG) measures the small magnetic fields generated by current flow in neural networks, providing a noninvasive metric of brain function. MEG is well established as a powerful neuroscientific and clinical tool. However, current instrumentation is hampered by cumbersome cryogenic field‐sensing technologies. In contrast, MEG using optically pumped magnetometers (OPM‐MEG) employs small, lightweight, noncryogenic sensors that provide data with higher sensitivity and spatial resolution, a natural scanning environment (including participant movement), and adaptability to any age. However, OPM‐MEG is new and the optimum way to design a system is unknown. Here, we construct a novel, 90‐channel triaxial OPM‐MEG system and use it to map motor function during a naturalistic handwriting task. Results show that high‐precision magnetic field control reduced background fields to ∼200 pT, enabling free participant movement. Our triaxial array offered twice the total measured signal and better interference rejection compared to a conventional (single‐axis) design. We mapped neural oscillatory activity to the sensorimotor network, demonstrating significant differences in motor network activity and connectivity for left‐handed versus right‐handed handwriting. Repeatability across scans showed that we can map electrophysiological activity with an accuracy ∼4 mm. Overall, our study introduces a novel triaxial OPM‐MEG design and confirms its potential for high‐performance functional neuroimaging.

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“…In this context, one might wonder whether a hypothetical magnetic version of ECoG, i.e., magnetocorticography, would lead to further improvements. Simulations suggest that scalp MEG might eventually outperform ECoG (Nugent et al, 2022), opening the possibility that the former replace the latter in the future. The remaining question is whether placing sensors directly on the neocortical surface (notwithstanding technical feasibility) would lead to even higher-resolution recordings of epilepsy.…”

Section: The Physics Of Meg Spatial Resolutionmentioning

confidence: 99%

Exploring the limits of MEG spatial resolution with multipolar expansions

Wens¹

2022

Preprint

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The advent of scalp magnetoencephalography (MEG) based on optically-pumped magnetometers (OPMs) may represent a step change in the field of human electrophysiology. Compared to cryogenic MEG based on superconducting quantum interference devices (SQUIDs, placed 2-4 cm above scalp), scalp MEG promises significantly higher spatial resolution imaging but it also comes with numerous challenges regarding how to optimally design OPM arrays. In this context, we sought to provide a systematic description of MEG spatial resolution as a function of the number of sensors (allowing comparison of low-vs. high-density MEG), sensor-to-brain distance (cryogenic SQUIDs vs. scalp OPM), sensor type (magnetometers vs. gradiometers; single-vs. multicomponent sensors), and signal-to-noise ratio. To that aim, we developped an analytical theory based on the physically-grounded technique of MEG multipolar expansions. In a first step, we show that the theory (together with experimental input) enables rigorous, analytical, and quantitative assessment of the limits of MEG spatial resolution in asymptotically high-density MEG. In a second step, we enlarge the theory using simulated data to encompass MEG at lower sensor density, and we build a full description in terms of two qualitatively distinct regimes. The resulting two-regime model of MEG spatial resolution integrates known observations (e.g., the difficulty of improving spatial resolution by increasing sensor density, the gain brought by moving sensors on scalp, or the usefulness of multi-component sensors) and gathers them under a unifying theoretical framework that highlights the underlying physical mechanisms. It also reveals new properties of the limits of MEG spatial resolution, such as their logarithmic divergence at asymptotically high density or their saturation as sensors approach sources of neural activity. We propose that this framework may find useful applications to benchmark the design of future OPM-based scalp MEG systems.

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On-scalp magnetocorticography with optically pumped magnetometers: Simulated performance in resolving simultaneous sources

Cited by 19 publications

References 48 publications

Magnetoencephalography with optically pumped magnetometers (OPM-MEG): the next generation of functional neuroimaging

Magnetoencephalography with optically pumped magnetometers (OPM-MEG): the next generation of functional neuroimaging

A 90‐channel triaxial magnetoencephalography system using optically pumped magnetometers

Exploring the limits of MEG spatial resolution with multipolar expansions

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