Where do we stand exactly with on‐scalp magnetoencephalography in the presurgical evaluation of refractory focal epilepsy?

Feys, Odile; Wens, Vincent; Corvilain, Pierre; Ferez, Maxime; Holmes, Niall; Brookes, Matthew; De Tiège, Xavier

doi:10.1111/epi.17806

Cited by 4 publications

(1 citation statement)

References 30 publications

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“…Nevertheless, the radial magnetic component remains a priori the optimal choice to record the signal of interest as it is larger in amplitude and less affected by volume conduction than tangential components ( Iivanainen et al, 2017 ). Thanks to their reduced size, Rb-OPMs can be placed directly on or very close to the scalp while recording physiological brain activity ( Boto et al, 2019 ; Borna et al, 2020 ; Boto et al, 2021 ) as well as epileptiform discharges in children ( Feys et al, 2022 , 2023a , b , d ) and adults ( Vivekananda et al, 2020 ; Hillebrand et al, 2023 ). In the case of pediatric epilepsy, the reduced brain-sensor distance afforded by on-scalp Rb-OPM-MEG led to higher IED amplitude and SNR compared with cryogenic MEG ( Feys et al, 2022 ).…”

Section: Introductionmentioning

confidence: 99%

Tri-axial rubidium and helium optically pumped magnetometers for on-scalp magnetoencephalography recording of interictal epileptiform discharges: a case study

Feys,

Corvilain,

Labyt

et al. 2023

Front. Neurosci.

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Cryogenic magnetoencephalography (MEG) enhances the presurgical assessment of refractory focal epilepsy (RFE). Optically pumped magnetometers (OPMs) are cryogen-free sensors that enable on-scalp MEG recordings. Here, we investigate the application of tri-axial OPMs [87Rb (Rb-OPM) and 4He gas (He-OPM)] for the detection of interictal epileptiform discharges (IEDs). IEDs were recorded simultaneously with 4 tri-axial Rb- and 4 tri-axial He-OPMs in a child with RFE. IEDs were identified visually, isolated from magnetic background noise using independent component analysis (ICA) and were studied following their optimal magnetic field orientation thanks to virtual sensors. Most IEDs (>1,000) were detectable by both He- and Rb-OPM recordings. IEDs were isolated by ICA and the resulting magnetic field oriented mostly tangential to the scalp in Rb-OPMs and radial in He-OPMs. Likely due to differences in sensor locations, the IED amplitude was higher with Rb-OPMs. This case study shows comparable ability of Rb-OPMs and He-OPMs to detect IEDs and the substantial benefits of triaxial OPMs to detect IEDs from different sensor locations. Tri-axial OPMs allow to maximize spatial brain sampling for IEDs detection with a limited number of sensors.

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Section: Introductionmentioning

confidence: 99%

Tri-axial rubidium and helium optically pumped magnetometers for on-scalp magnetoencephalography recording of interictal epileptiform discharges: a case study

Feys,

Corvilain,

Labyt

et al. 2023

Front. Neurosci.

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A Novel, Robust, and Portable Platform for Magnetoencephalography using Optically Pumped Magnetometers

Schofield,

Hill,

Feys

et al. 2024

Preprint

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Magnetoencephalography (MEG) measures brain function via assessment of magnetic fields generated by neural currents. Conventional MEG uses superconducting sensors, which place significant limitations on performance, practicality, and deployment; however, the field has been revolutionised in recent years by the introduction of optically-pumped-magnetometers (OPMs). OPMs enable measurement of the MEG signal without cryogenics, and consequently the conception of ‘OPM-MEG’ systems which ostensibly allow increased sensitivity and resolution, lifespan compliance, free subject movement, and lower cost. However, OPM-MEG remains in its infancy with limitations on both sensor and system design. Here, we report a new OPM-MEG design with miniaturised and integrated electronic control, a high level of portability, and improved sensor dynamic range (arguably the biggest limitation of existing instrumentation). We show that this system produces equivalent measures when compared to an established instrument; specifically, when measuring task-induced beta-band, gamma-band and evoked neuro-electrical responses, source localisations from the two systems were highly comparable and temporal correlation was >0.7 at the individual level and >0.9 for groups. Using an electromagnetic phantom, we demonstrate improved dynamic range by running the system in background fields up to 8 nT. We show that the system is effective in gathering data during free movement (including a sitting-to-standing paradigm) and that it is compatible with simultaneous electroencephalography (EEG – the clinical standard). Finally, we demonstrate portability by moving the system between two laboratories. Overall, our new system is shown to be a significant step forward for OPM-MEG technology and offers an attractive platform for next generation functional medical imaging.

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On-scalp magnetoencephalography based on optically pumped magnetometers to investigate temporal lobe epilepsy

Feys,

Wens,

Depondt

et al. 2024

Preprint

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Cryogenic magnetoencephalography (MEG) has a lower yield in temporal lobe epilepsy (TLE) than in extra-TLE (ETLE). The advent of optically pumped magnetometers (OPMs) might change this thanks to on-scalp MEG, which allows sensors to be placed closer to the brain and the design of bespoke sensor arrays to target specific brain regions. This study aims to investigate the detection and localization accuracy of interictal epileptiform discharges (IEDs) using on-scalp MEG in TLE and the added-value of face-OPMs for temporal IED detection/localization.Eleven patients underwent a 1-h MEG recording with OPMs placed both on the scalp (flexible cap, scalp-OPMs) and on the face (3D-printed glass-like structure, face-OPMs). Nine patients also underwent cryogenic MEG. IEDs were visually detected, averaged and localized using distributed source reconstruction. On-scalp MEG IED amplitude and signal-to-noise (SNR) were assessed and compared with cryogenic MEG when more than 10 IEDs were detected. Neural sources with and without face-OPMs were compared. The correlation between face- and scalp-OPMs was assessed.A mean of 13 IEDs/patient was detected using on-scalp MEG (mean amplitude: 3.3pT, mean SNR: 9.4) and localized in the (medial, anterior, basal, lateral or posterior) temporal lobe. Three patients had >10 IEDs in on-scalp and cryogenic MEG signals with amplitude and SNR that were either higher or similar for the on-scalp MEG recording compared with cryogenic MEG, and sources were separated by 8-11 mm. In two other patients, on-scalp MEG source locations were confirmed by gold-standard methods (surgical resection cavity, n=1; stereo-electroencephalography, n=1). Face-OPMs had a clear added-value (i.e., IED detection and localization) in one patient with antero-medial TLE. Face-OPM signals were correlated with scalp-OPM signals in most patients, showing that face-OPMs recorded brain activity.This study shows that on-scalp MEG is able to detect and localize IEDs in TLE and to discriminate irritative zones from different key (medial, anterior, basal, lateral or postero-lateral) temporal areas with similar or enhanced SNR than cryogenic MEG. Face-OPMs have a clear added-value in patients with anterior/medial TLE and increase the spatial coverage of the temporal lobe. This study paves the way for the future use of on-scalp MEG in patients with refractory TLE and patients with other brain disorders affecting the temporal lobe such as Alzheimer’s disease.

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Where do we stand exactly with on‐scalp magnetoencephalography in the presurgical evaluation of refractory focal epilepsy?

Cited by 4 publications

References 30 publications

Tri-axial rubidium and helium optically pumped magnetometers for on-scalp magnetoencephalography recording of interictal epileptiform discharges: a case study

Tri-axial rubidium and helium optically pumped magnetometers for on-scalp magnetoencephalography recording of interictal epileptiform discharges: a case study

A Novel, Robust, and Portable Platform for Magnetoencephalography using Optically Pumped Magnetometers

On-scalp magnetoencephalography based on optically pumped magnetometers to investigate temporal lobe epilepsy

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