On-scalp magnetoencephalography for childhood epilepsies

Abstract

Magnetoencephalography (MEG) is an established method to investigate epilepsy. Current MEG systems house hundreds of cryogenic sensors in a rigid, one-size-fits-all helmet, which results in several limitations, particularly in children. On-scalp MEG based on optically-pumped magnetometers (OPMs) may alleviate these limitations. We report on five children (5-11 years old) with self-limited focal (n=3) or structural (n=2) epilepsy who underwent cryogenic (102 magnetometers) and on-scalp (32 OPMs) MEG. We compared the two modalities for the detection and localization of interictal epileptiform discharges (IEDs). We identified IEDs in all children with comparable sensor topographies for both MEG devices. IED amplitudes were 2.3-4.8 times higher with on-scalp MEG and signal-to-noise ratio (SNR) was also 27-60% higher with on-scalp MEG in all but one patient with large head movement artifacts. The neural source of averaged IEDs was located at about 5 mm (n=3) or higher (8.3 mm, n=1; 15.6 mm, n=1) between on-scalp and cryogenic MEG. Despite limited number of sensors and scalp coverage, on-scalp MEG detects IEDs in epileptic children with higher SNR than cryogenic MEG. This technology, which is in constant development, should become a reference in the diagnostic workup of epilepsy and replace cryogenic MEG in the near future.

First experiences of whole-head OP-MEG recordings from a patient with Epilepsy

“…This provides a certain degree of confidence that our OP-MEG recordings could be useful for delineating the epileptogenic zone and supports the need for studies in larger numbers of patients with surgical outcome data. Additionally, and reassuringly, Feys et al, (2021) have shown a direct and compelling comparison between OPM and SQUID recordings in the estimated epileptogenic zone in 5 children with epilepsy.…”

“…This means that it is possible to capture maximal signal for any head-size. This can increase the SNR of observed interictal epileptiform discharges (Feys et al ., 2021) and it has been shown with high-T C on-scalp SQUID-MEG, that higher proximity of the sensors to the scalp can increase the number of interictal discharges that are observed (Westin et al ., 2020). This improvement would be particularly important for children, due to their smaller head size (Boto et al ., 2016; Hill et al ., 2019) and is pertinent for epilepsy since there is an incidence peak in childhood (Kotsopoulos et al ., 2002; Fiest et al ., 2017).…”

“…Previous OP-MEG studies have demonstrated epileptogenic discharges in mice (Alem et al ., 2014), in a single subject (Vivekananda et al ., 2020) and in 5 pediatric patients (Feys et al ., 2021). One of the main applications for OP-MEG in epilepsy is identification of the epileptogenic focus for pre-surgical planning.…”

Pediatric magnetoencephalography

“…MEG can be particularly helpful in cases of frontal lobe epilepsy that masquerade as a generalized epilepsy on the scalp EEG recording. 12 It also has distinct advantages in identifying seizures of deep tissue onset.…”

“…Identifying the irritative zone helps epileptologists and neurosurgeons plan surgeries with good hypotheses in order to create the best possible blueprint to obtain meaningful information from invasive recording. MEG can be particularly helpful in cases of frontal lobe epilepsy that masquerade as a generalized epilepsy on the scalp EEG recording 12 . It also has distinct advantages in identifying seizures of deep tissue onset.…”