Calibration and Localization of Optically Pumped Magnetometers Using Electromagnetic Coils

Area of Science:

• Biophysics
• Biomedical Engineering
• Sensor Technology

Background:

• Accurate calibration of magnetic field sensors is critical for high-resolution neuroimaging techniques like magnetoencephalography (MEG).
• Optically Pumped Magnetometers (OPMs) offer enhanced sensitivity but require precise calibration of their position, orientation, and gain.
• Existing calibration methods can be complex and time-consuming.

Purpose of the Study:

• To develop and validate a novel method for calibrating OPMs using a set of electromagnetic coils.
• To accurately estimate the position, orientation, and gain of individual OPM sensors within an array.
• To assess the performance of the proposed calibration method for magnetoencephalography (MEG) applications.

Main Methods:

• Utilized a system of large electromagnetic coils to generate known magnetic fields.
• Measured coil fields at multiple positions with a calibrated triaxial magnetometer and modeled them using vector spherical harmonics (VSH).
• Calibrated OPMs by minimizing errors between VSH model signals and OPM responses, employing linear equations derived from homogeneous and first-order gradient fields.

Main Results:

• Demonstrated accurate estimation of OPM sensor parameters (position, orientation, gain) using the coil-based method.
• Achieved root-mean-square (RMS) errors of 1.0 mm for position, 0.2° for orientation, and 0.8% for gain in initial fluxgate magnetometer tests.
• Validated the method by calibrating a 48-channel OPM array, achieving an average dipole position error of 3.3 mm in phantom tests.

Conclusions:

• The proposed electromagnetic coil-based method provides a feasible and accurate approach for calibrating OPMs.
• This technique is suitable for preparing OPM arrays for advanced applications such as magnetoencephalography (MEG).
• The method offers a computationally efficient way to determine essential OPM sensor parameters.