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

Cryogenic magnetoencephalography (MEG) has a lower yield in temporal lobe epilepsy (TLE) than in extratemporal lobe epilepsy. The advent of optically pumped magnetometers (OPMs) might change this situation thanks to on‐scalp MEG. This study aims to investigate the detection/localization accuracy of interictal epileptiform discharges (IEDs) using on‐scalp MEG in TLE and the added value of face‐OPMs. Eleven patients underwent a 1‐h MEG recording with OPMs placed both on the scalp (flexible cap, scalp‐OPMs) and on the face (glasseslike structure, face‐OPMs). Nine patients underwent cryogenic MEG. IED amplitude and signal‐to‐noise ratio (SNR) were compared when ≥10 IEDs were detected. A mean of 13 IEDs/patient were detected using on‐scalp MEG (mean amplitude = 3.3 pT, mean SNR = 9.4) and localized in the (medial, anterior, basal, lateral, posterior) temporal lobe. Amplitude and SNR were either higher or similar between on‐scalp and cryogenic MEG, with neural sources separated by 6–16 mm. In two patients, on‐scalp MEG source locations were confirmed by surgical resection cavity or stereoelectroencephalography. Face‐OPMs had a clear added value in one patient with anteromedial TLE. On‐scalp MEG can detect/localize IEDs in TLE. Face‐OPMs may have added value in patients with anterior/medial TLE and increase the spatial coverage of the temporal lobe. This study paves the way for the use of on‐scalp MEG in patients with refractory TLE.