Real-Time Localization of OPMs in a Flexible Array during MEG Recordings

Optically pumped magnetometers (OPMs) are typically designed as standalone sensors that are positionally adjustable for use in OPM-magnetoencephalography (MEG), allowing for a flexible spatial layout of the OPM array that can fit individual scalp shapes. This design reduces the sensor-to-source distance, thereby enhancing the signal strength measured by OPMs. However, due to the lack of continuous tracking of OPM locations, unnoticed displacement of OPMs during MEG recordings can introduce errors into the forward modeling of OPM-MEG and, consequently, the reconstruction of neural activities. In this study, we developed a real-time OPM localization system using capacitive displacement transducers (CDTs) to accurately and dynamically depict the spatial configuration of the OPM array during MEG recordings. The CDT's displacement measurement precision reached 0.1 mm, and its magnetic field interference with OPMs was negligible. Therefore, we could simultaneously acquire the locations and MEG measurements of OPMs. Furthermore, we proposed an efficient workflow to automatically match OPM locations with the scalp surface within 10 seconds.