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B. and Ruth H. Dunn Charitable Foundation","award":["EP\/T001046\/1"],"award-info":[{"award-number":["EP\/T001046\/1"]}]},{"name":"R. B. and Ruth H. Dunn Charitable Foundation","award":["EP\/V047264\/1"],"award-info":[{"award-number":["EP\/V047264\/1"]}]},{"name":"R. B. and Ruth H. Dunn Charitable Foundation","award":["R01EB028772"],"award-info":[{"award-number":["R01EB028772"]}]},{"name":"R. B. and Ruth H. Dunn Charitable Foundation","award":["R21EB033577"],"award-info":[{"award-number":["R21EB033577"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>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.<\/jats:p>","DOI":"10.3390\/s23146537","type":"journal-article","created":{"date-parts":[[2023,7,20]],"date-time":"2023-07-20T05:42:01Z","timestamp":1689831721000},"page":"6537","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["An Iterative Implementation of the Signal Space Separation Method for Magnetoencephalography Systems with Low Channel Counts"],"prefix":"10.3390","volume":"23","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0561-8366","authenticated-orcid":false,"given":"Niall","family":"Holmes","sequence":"first","affiliation":[{"name":"Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK"},{"name":"Cerca Magnetics Limited, Unit 2 Castlebridge Office Village, Kirtley Drive, Nottingham NG7 1LD, UK"}]},{"given":"Richard","family":"Bowtell","sequence":"additional","affiliation":[{"name":"Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK"}]},{"given":"Matthew J","family":"Brookes","sequence":"additional","affiliation":[{"name":"Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK"},{"name":"Cerca Magnetics Limited, Unit 2 Castlebridge Office Village, Kirtley Drive, Nottingham NG7 1LD, UK"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6164-3366","authenticated-orcid":false,"given":"Samu","family":"Taulu","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Washington, Seattle, WA 98195, USA"},{"name":"Institute for Learning and Brain Sciences, University of Washington, Seattle, WA 98195, USA"}]}],"member":"1968","published-online":{"date-parts":[[2023,7,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"784","DOI":"10.1126\/science.161.3843.784","article-title":"Magnetoencephalography: Evidence of Magnetic Fields Produced by Alpha Rhythm Currents","volume":"161","author":"Cohen","year":"1968","journal-title":"Science"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"413","DOI":"10.1103\/RevModPhys.65.413","article-title":"Magnetoencephalography Theory, Instrumentation, and Applications to Noninvasive Studies of the Working Human Brain","volume":"65","author":"Hari","year":"1993","journal-title":"Rev. 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