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

Front Neurosci. 2023 Nov 27:17:1284262. doi: 10.3389/fnins.2023.1284262. eCollection 2023.

Abstract

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.

Keywords: focal epilepsy; magnetoencephalography; on-scalp magnetoencephalography; optically pumped magnetometers; refractory epilepsy.

Publication types

  • Case Reports

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. OF was supported by the Fonds pour la formation à la recherche dans l’industrie et l’agriculture [FRIA, Fonds de la Recherche Scientifique (FRS-FNRS), Brussels, Belgium]. PC was supported by the Fonds Erasme (Convention « Alzheimer », Brussels, Belgium). XDT was Clinical Researcher at the FRS-FNRS. The OPM-MEG project at the Hôpital Universitaire de Bruxelles and Université libre de Bruxelles is financially supported by the Fonds Erasme (Projet de Recherche Clinique et Convention « Les Voies du Savoir 2 ») and by the FRS-FNRS (Crédit de Recherche: J.0043.20F, Crédit Équipement: U.N013.21F). The MAGIC OPM MEG project at CEA Tech Lille, Amiens and Lille University Hospitals and Université de Picardie Jules Verne and Université de Lille was co-funded by European Union with the European Funding of Regional Development and the Region Hauts de France.