A bi-planar coil system for nulling background magnetic fields in scalp mounted magnetoencephalography.

摘要: Small, commercially-available Optically Pumped Magnetometers (OPMs) can be used to construct a wearable Magnetoencephalography (MEG) system that allows large head movements made during recording. The small dynamic range of these sensors however means movement in the residual static magnetic field found inside typical Magnetically Shielded Rooms (MSRs) saturate sensor outputs, rendering data unusable. This problem ameliorated by using set electromagnetic coils attenuate spatially-varying remnant field. Here, an array bi-planar coils, which produce open and accessible scanning environment, was designed constructed. were harmonic minimisation method previously for gradient coil design Magnetic Resonance Imaging (MRI). Six constructed null Bx, By Bz as well three dominant gradients dBx/dz, dBy/dz dBz/dz. homogeneous (within ±5%) fields or over volume 40 × 40 × 40 cm3. is sufficient contain OPMs, mounted 3D-printed scanner-cast, basic natural movements. Automated control reference measurements reduction largest component (Bx) from 21.8 ± 0.2 nT 0.47 ± 0.08 nT. (dBx/dz) reduced 7.4 nT/m 0.55 nT/m. High precision optical tracking allowed experiments involving controlled measured movements, revealed rotation scanner-cast ±34° translation ±9.7 cm OPMs this generated only 1 nT variation across OPM array, when nulling applied. could further 0.04 nT linear regression variations correlated with motion parameters. To demonstrate effectiveness cancellation real MEG experiment, novel measurement retinotopy investigated, where stimulus remains fixed subject shift visual presentation lower left right quadrants view. Left stimulation produced expected responses opposing hemisphere. simple demonstration shows accurate OPM-MEG recordings on unrestrained subject.