Choice of Magnetometers and Gradiometers after Signal Space Separation


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Garcés, Pilar and López-Sanz, David and Maestú Unturbe, Fernando and Pereda, Ernesto (2017) Choice of Magnetometers and Gradiometers after Signal Space Separation. Sensors, 17 (12). p. 2926. ISSN 1424-8220

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Background: Modern Elekta Neuromag MEG devices include 102 sensor triplets containing one magnetometer and two planar gradiometers. The first processing step is often a signal space separation (SSS), which provides a powerful noise reduction. A question commonly raised by researchers and reviewers relates to which data should be employed in analyses: (1) magnetometers only, (2) gradiometers only, (3) magnetometers and gradiometers together. The MEG community is currently divided with regard to the proper answer.
Methods: First, we provide theoretical evidence that both gradiometers and magnetometers result from the backprojection of the same SSS components. Then, we compare resting state and task-related sensor and source estimations from magnetometers and gradiometers in real MEG recordings before and after SSS.
Results: SSS introduced a strong increase in the similarity between source time series derived from magnetometers and gradiometers (r2 = 0.3–0.8 before SSS and r2 > 0.80 after SSS). After SSS, resting state power spectrum and functional connectivity, as well as visual evoked responses, derived from both magnetometers and gradiometers were highly similar (Intraclass Correlation Coefficient > 0.8, r 2 > 0.8).
Conclusions: After SSS, magnetometer and gradiometer data are estimated from a single set of SSS components (usually ≤ 80). Equivalent results can be obtained with both sensor types in typical MEG experiments.

Item Type:Article
Uncontrolled Keywords:Magnetoencephalography; signal space separation; magnetometer; gradiometer; beamforming; regularization
Subjects:Medical sciences > Psychology > Experimental psychology
ID Code:62235
Deposited On:22 Sep 2020 07:54
Last Modified:22 Sep 2020 07:54

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