Optimal configuration of on-scalp OPMs with fixed channel counts

Area of Science:

• Neuroscience
• Biophysics
• Biomedical Engineering

Background:

• Optically pumped magnetometers (OPMs) are emerging as a transformative technology for magnetoencephalography (MEG) in neuroscience.
• Current whole-head MEG systems utilize OPMs, with sensor configurations varying in the number of measurement orientations and locations.
• Optimizing OPM system design, including sensor placement and orientation, is crucial for maximizing data quality under practical constraints.

Purpose of the Study:

• To investigate the optimal spatial distribution and sensing orientation of OPMs for MEG.
• To compare the performance of monoaxial, biaxial, and triaxial OPM arrays with a constant number of channels.
• To guide the design of future OPM-based MEG systems for improved brain activity measurement and noise suppression.

Main Methods:

• A simulation study was conducted using 192-channel OPM arrays with monoaxial, biaxial, and triaxial sensors at varying locations.
• Simulated MEG signals from dipolar brain sources were generated, incorporating sensor, brain, and movement-induced noise.
• Dipole fitting analysis was performed on cleaned data to evaluate localization error and dipole moment amplitude.

Main Results:

• Radial sensing orientations are generally superior for detecting brain activity compared to tangential ones.
• Incorporating tangential sensing orientations aids in the suppression of ambient noise.
• No significant performance improvement was observed when comparing triaxial sensors to biaxial sensors.

Conclusions:

• Biaxial OPM sensors appear to be the preferred choice over triaxial sensors when the number of channels is fixed, considering current technological limitations.
• Triaxial sensing may lead to reduced spatial sampling and signal-to-noise ratio per channel.
• The findings provide valuable insights for the practical design and implementation of OPM-based MEG systems.