Unleashing the Potential of ⁴ He OPM-MEG: A Comparison with SQUID-MEG for Detecting Interictal Epileptic Activity

Objectives

Conventional magnetoencephalography (MEG) based on superconducting quantum interference devices sensors (SQUIDs), are the only widely used MEG systems in both clinical and research settings. However, they have limitations that hinder their widespread deployment. Optically pumped magnetometers (OPMs) offer several advantages over SQUIDs, particularly for epilepsy studies: lightweight and flexible, OPMs can be integrated into adaptable motion-tolerant headsets, enabling recordings during seizures or natural head movements, and potentially enhancing the detection of interictal epileptiform discharges (IEDs). In the present study, we assess the capabilities of a 5-sensors MEG system with helium OPMs ( ⁴ He-OPMs) in detecting IEDs.

Methods

First, we compare the performance of SQUID-MEG and ⁴ He-OPM-MEG in a routine clinical setup with a group of 7 patients. Second, we perform combined intra-cerebral (SEEG) ⁴ He-OPM-MEG and SQUID-MEG recordings in a single patient to demonstrate the ability of both systems to detect IEDs originating from deep brain structures.

Results

The key finding is that, even with a very limited number of sensors, the ⁴ He-OPM-MEG prototype successfully captured interictal epileptic activity in most patients. This activity was clearly detectable and exhibited the characteristic morphology with strikingly similar time courses between ⁴ He-OPM-MEG and SQUID-MEG signals. Using combined SEEG and OPM-MEG recordings, we obtained the first direct validation of the ability of ⁴ He OPM sensors to record epileptic activities originating from deep structures.

Significance

These results strongly support the clinical adoption of a lightweight, high-sensitivity, whole-head ⁴ He OPMs-MEG system, offering new perspectives for epilepsy diagnostics and beyond, and enabling the democratization and spread of MEG in clinical and research settings.

Plain language summary

Magnetoencephalography is a non-invasive neuroimaging technique that has been shown to improve surgical outcomes in epileptic patients. However, its use remains limited due to several constraints, which could be overcome by a new generation of sensors: the optically pumped magnetometers (OPMs). Here, we validate the ability of OPM sensors to record epileptic brain activity in a regular clinical setup and thanks to simultaneous intracerebral recordings. These sensors open new venues for the widespread application of magnetoencephalography in the management of epilepsy and other neurological diseases, as well as for fundamental neuroscience.

Key points

• Epileptic abnormalities are detected by ⁴ He OPMs as well as with classical magnetoencephalography.

• Hippocampal interictal activity can be detected by ⁴ He OPMs as shown by simultaeous SEEG-OPM recordings.

• This results represents significant step towards the validation of OPM-MEG for epilepsy diagnosis and neuroscience research.