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An Iterative Implementation of the Signal Space Separation Method for Magnetoencephalography Systems with Low Channel Counts

Holmes, Niall; Bowtell, Richard; Brookes, Matthew J; Taulu, Samu

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Authors

NIALL HOLMES NIALL.HOLMES@NOTTINGHAM.AC.UK
Mansfield Research Fellow

Samu Taulu



Abstract

The signal space separation (SSS) method is routinely employed in the analysis of multichannel magnetic field recordings (such as magnetoencephalography (MEG) data). In the SSS method, signal vectors are posed as a multipole expansion of the magnetic field, allowing contributions from sources internal and external to a sensor array to be separated via computation of the pseudo-inverse of a matrix of the basis vectors. Although powerful, the standard implementation of the SSS method on MEG systems based on optically pumped magnetometers (OPMs) is unstable due to the approximate parity of the required number of dimensions of the SSS basis and the number of channels in the data. Here we exploit the hierarchical nature of the multipole expansion to perform a stable, iterative implementation of the SSS method. We describe the method and investigate its performance via a simulation study on a 192-channel OPM-MEG helmet. We assess performance for different levels of truncation of the SSS basis and a varying number of iterations. Results show that the iterative method provides stable performance, with a clear separation of internal and external sources.

Citation

Holmes, N., Bowtell, R., Brookes, M. J., & Taulu, S. (2023). An Iterative Implementation of the Signal Space Separation Method for Magnetoencephalography Systems with Low Channel Counts. Sensors, 23(14), Article 6537. https://doi.org/10.3390/s23146537

Journal Article Type Article
Acceptance Date Jul 16, 2023
Online Publication Date Jul 20, 2023
Publication Date Jul 2, 2023
Deposit Date Aug 21, 2023
Publicly Available Date Aug 23, 2023
Journal Sensors
Electronic ISSN 1424-8220
Publisher MDPI
Peer Reviewed Peer Reviewed
Volume 23
Issue 14
Article Number 6537
DOI https://doi.org/10.3390/s23146537
Keywords optically pumped magnetometer; magnetoencephalography; SSS; MEG analysis
Public URL https://nottingham-repository.worktribe.com/output/23861581
Publisher URL https://www.mdpi.com/1424-8220/23/14/6537

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