Effects of head modeling errors on the spatial frequency representation of MEG.

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Abstract

We aim to investigate the effects of head model inaccuracies on signal and source reconstruction accuracies for various sensor array distances to the head. This allows for the assessment of the importance of head modeling for next-generation magnetoencephalography (MEG) sensors, optically-pumped magnetometers (OPM).A 1-shell boundary element method (BEM) spherical head model with 642 vertices was defined. The vertices were randomly perturbed radially up to 2% – 10% of the radius, and the forward signal was calculated for dipolar sources located at 2 cm to 8 cm from the center of the sphere with a 324 sensor array located at 10 cm to 15 cm from the center of the sphere. Source localization was performed for each of these forward signals. The signal for each perturbed spherical head case was analyzed in the spatial frequency domain, and the signal and source localization errors were quantified relative to the unperturbed case.In the noiseless and high signal-to-noise ratio (SNR) case of approximately >= 6 dB, inaccuracies in our spherical BEM head model led to increased signal and source localization inaccuracies when sensor arrays were closer to the head, especially for deep and superficial sources. In the noisy case however, the higher SNR for closer sensor arrays led to an improved ECD fit and outweighed the effects of head geometry inaccuracies.OPMs may be placed directly on the head, as opposed to the more commonly used superconducting quantum interference device (SQUID) sensors which must be placed a few centimeters away from the head. OPMs thus allow for signals of higher spatial resolution to be captured, resulting in potentially more accurate source localizations. Our results suggest that an increased emphasis on accurate head modeling for OPMs may be necessary to fully realize its improved source localization potential.Creative Commons Attribution license.