PEDIATRIC IMAGING D rug-resistant epilepsy occurs in one-third of patients with epilepsy (1). The main treatment to alleviate seizures in those patients is epilepsy surgery, provided that the presumed location of the epileptogenic zone (PLEZ) is focal, well localized, and does not involve functionally eloquent cortices (1). Magnetoencephalography (MEG) provides nonredundant information for the noninvasive localization of the PLEZ in patients with refractory focal epilepsy (RFE) (2,3).Cryogenic MEG systems house hundreds of superconducting quantum interference devices (SQUIDs) in a rigid, one-size-fits-all helmet (4). SQUIDs have several major limitations (4). Due to cryogenic cooling, a thermally insulated gap is required between the scalp and SQUIDs, meaning that the brain-to-sensor distance is approximately 2-5 cm in adults who fit the system well and larger in patients with small heads, such as children. Small head size increases the brain-to-sensor signal attenuation as magnetic fields decrease with the square of the distance. Pediatric SQUID-based MEG (hereafter, SQUID-MEG) systems do not fully alleviate those limitations as they restrict the use of MEG to specific age ranges (eg, infants or school-aged children) (5).Optically pumped magnetometers (OPMs) are cryogen-free magnetic field sensors. OPMs can be placed directly on the scalp to record neuromagnetic signals with an Purpose: To determine if on-scalp MEG based on optically pumped magnetometers (OPMs) alleviates the main limitations of cryogenic MEG. Materials and Methods:In this prospective single-center study conducted in a tertiary university teaching hospital, participants underwent cryogenic (102 magnetometers, 204 planar gradiometers) and on-scalp (32 OPMs) MEG. The two modalities for the detection and localization of IEDs were compared. The t test was used to compare IED amplitude and signal-to-noise ratio (SNR). Distributed source modeling was performed on OPM-based and cryogenic MEG data.Results: Five children (median age, 9.4 years [range, 5-11 years]; four girls) with self-limited idiopathic (n = 3) or refractory (n = 2) focal epilepsy were included. IEDs were identified in all five children with comparable sensor topographies for both MEG devices. IED amplitudes were 2.3 (7.2 of 3.1) to 4.6 (3.2 of 0.7) times higher (P , .001) with on-scalp MEG, and the SNR was 27% (16.7 of 13.2) to 60% (12.8 of 8.0) higher (P value range: .001-.009) with on-scalp MEG in all but one participant (P = .93), whose head movements created pronounced motion artifacts. The neural source of averaged IEDs was located at approximately 5 mm (n = 3) or higher (8.3 mm, n = 1; 15.6 mm, n = 1) between on-scalp and cryogenic MEG. Conclusion:Despite the limited number of sensors and scalp coverage, on-scalp magnetoencephalography (MEG) based on optically pumped magnetometers helped detect interictal epileptiform discharges in school-aged children with epilepsy with a higher amplitude, higher signal-to-noise ratio, and similar localization value compared with conventional cr...

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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.