On-scalp MEG sensor localization using magnetic dipole-like coils: A method for highly accurate co-registration

Area of Science:

• Biophysics
• Neuroimaging
• Biomedical Engineering

Background:

• Magnetoencephalography (MEG) source modeling necessitates accurate alignment of sensor arrays with individual head anatomy.
• Conventional MEG relies on fixed sensor positions, requiring only head localization.
• On-scalp MEG systems face challenges as sensor positions vary with head shape, demanding individual sensor localization for each recording.

Purpose of the Study:

• To develop and validate a practical method for localizing sensors in on-scalp magnetoencephalography (MEG) systems.
• To enable precise co-registration of on-scalp sensors with individual head anatomy for improved source modeling.
• To establish a method for continuous and accurate sensor localization in on-scalp MEG.

Main Methods:

• A novel method using magnetic dipole-like coils attached to the subject's head was developed for sensor localization.
• The method was implemented and evaluated on a 7-channel on-scalp MEG system utilizing high-temperature superconducting quantum interference devices (high-T_c SQUIDs).
• Sensor positions, orientations, and responsivities were individually localized using short averaging times, with further accuracy improvements through joint calibration and localization.

Main Results:

• The developed method achieved high accuracy in localizing individual sensor positions (≤ 2 mm), orientations (< 3°), and responsivities (< 3%) with 1-second averaging.
• Joint calibration and localization further enhanced positional and orientational accuracy (< 1 mm, < 1°).
• Source localization of somatosensory evoked activity using the on-scalp system demonstrated comparable results (within 4.2 mm) to a commercial whole-head MEG system.

Conclusions:

• This practical method enables accurate and continuous localization of on-scalp MEG sensors, crucial for precise source modeling.
• The findings facilitate improved brain activity mapping with on-scalp MEG systems by ensuring reliable sensor-to-head co-registration.
• The developed technique offers a viable solution for overcoming the challenges of sensor positioning variability in on-scalp MEG recordings.