Magnetically Shielded Room Internal Depth Compensation and Wearable MEG Motion Measurement With Large Spatial Range

The static magnetic field within magnetically shielded room (MSR) is a main factor restricting magnetoencephalography (MEG) if measurements for a moving subject with optically pumped magnetometers (OPMs) are carried out. Existing compensation methods can control it at the nanotesla or sub-nanotesla level, which can meet the measurement during subjects' stationary or small-scale movements. However, this still brings significant motion artifacts. This article studies the spatial distribution characteristics of static residual magnetic fields inside the MSR, and proposes a hybrid coil compensation system. A magnetic field component model is established for all types of coils in the hybrid coil compensation system at various points in space. Then, the distribution pattern of the minimum sensor array and the number of sensors for real-time observation of the magnetic field in space were discussed. Combined with a genetic algorithm (GA), the coil current is optimized to achieve large-scale measurement of motion MEG. The static magnetic field in the central volume of 60×60×15 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> is monitored, and the three static magnetic field components within areas of 10×20 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, 30×40 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 50×60 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were accurately controlled to less than 55 pT, 95 pT and 170 pT respectively. Finally, the reliability of the compensation system and algorithm control is verified through auditory stimulation experiments, laying a foundation for the study of motion MEG.