Source-level performance of triaxial and uniaxial-radial OPM-MEG

Magnetoencephalography (MEG) based on optically pumped magnetometers (OPM) provides a new means for detecting human brain activities. Compared to conventional SQUID-MEG, OPM-MEG offers significant advantages, including the wearability, flexibility in sensor arrays, ability to operate at room temperature, and closer proximity to the scalp for stronger signals. Initially, the OPM with uniaxial sensitivity has been widely used for measuring the radial magnetic field components relative to the scalp. Recently, triaxial OPM has become a mainstream development trend, enabling OPM-MEG to measure the full neuromagnetic field vector. Studies have shown that triaxial OPM-MEG provides sensitivity to the tangential components of the magnetic field, offers greater brain coverage, and exhibits enhanced motion-artifact resistance compared to uniaxial OPM-MEG. However, source-level performance disparities between triaxial and uniaxial OPM-MEG remain underexplored. Here, we comprehensively evaluated the source-level performance of triaxial and uniaxial OPM-MEG using five source reconstruction methods. The analysis is performed under various simulation conditions, including various extents, numbers, correlation coefficients, and depth of sources, SNRs, co-registration errors. The results show that triaxial OPM-MEG significantly improves source imaging accuracy in most cases over uniaxial systems. Importantly, this advantage exhibits strong method dependence. In addition, we validated the conclusions obtained from the simulation in publicly available 64 triaxial OPM-MEG (192 channels of data) somatosensory data. A guideline for the selection of imaging methods in various real-world scenarios is provided based on our findings.