Calibration and Localization of Optically Pumped Magnetometers Using Electromagnetic Coils

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Sensors, Volume 22, issue 8
In this paper, we propose a method to estimate the position, orientation, and gain of a magnetic field sensor using a set of (large) electromagnetic coils. We apply the method for calibrating an array of optically pumped magnetometers (OPMs) for magnetoencephalography (MEG). We first measure the magnetic fields of the coils at multiple known positions using a well‐calibrated triaxial magnetometer, and model these discreetly sampled fields using vector spherical harmonics (VSH) functions. We then localize and calibrate an OPM by minimizing the sum of squared errors between the model signals and the OPM responses to the coil fields. We show that by using homogeneous and first‐order gradient fields, the OPM sensor parameters (gain, position, and orientation) can be obtained from a set of linear equations with pseudo‐inverses of two matrices. The currents that should be applied to the coils for approximating these low‐order field components can be determined based on the VSH models. Computationally simple initialestimates of the OPM sensor parameters follow. As a first test of the method, we placed a fluxgate magnetometer at multiple positions and estimated the RMS position, orientation, and gain errors of the method to be 1.0 mm, 0.2°, and 0.8%, respectively. Lastly, we calibrated a 48‐channel OPM array. The accuracy of the OPM calibration was tested by using the OPM array to localize magnetic dipoles in a phantom, which resulted in an average dipole position error of 3.3 mm. The results demonstrate the feasibility of using electromagnetic coils to calibrate and localize OPMs for MEG.
| openaire: EC/H2020/678578/EU//HRMEG Funding Information: Acknowledgments: Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC—a wholly owned subsidiary of Honeywell International Inc.—for the U.S. Department of Energy’s National Nuclear Security Admin‐ istration, under contract DENA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy, the United States Government, the National Institutes of Health, or the European Research Council. The content is solely the responsibility of the authors. Funding Information: Funding: Research reported in this publication was supported by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health, under award number U01EB028656, and the European Research Council, under grant agreement No 678578 (project HRMEG). Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
calibration, co‐registration, electromagnetic coil, fluxgate magnetometer, magnetoencephalography, on‐scalp MEG, optically pumped magnetometer, sensor localization
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Iivanainen , J , Borna , A , Zetter , R , Carter , T R , Stephen , J M , McKay , J , Parkkonen , L , Taulu , S & Schwindt , P D D 2022 , ' Calibration and Localization of Optically Pumped Magnetometers Using Electromagnetic Coils ' , Sensors , vol. 22 , no. 8 , 3059 , pp. 1-17 .