A simplex method for the calibration of a MEG device

Open access


MagnetoEncephaloGraphy (MEG) devices are helmet–shaped arrays of sensors that measure the tiny magnetic fields produced by neural currents. As they operate at low temperature, they are typically immersed in liquid helium. However, during the cooling process the sensor position and shape can change, with respect to nominal values, due to thermal stress. This implies that an accurate sensor calibration is required before a MEG device is utilized in either neuroscientific research or clinical workflow. Here we describe a calibration scheme developed for the optimal use of a MEG system recently realized at the “Istituto di Cibernetica e Biofisica” of the Italian CNR. To achieve the calibration goal a dedicated magnetic source is used (calibration device) and the geometric parameters of the sensors are determined through an optimisation procedure, based on the Nelder-Mead algorithm, which maximises the correlation coefficient between the predicted and the recorded magnetic field. Then the sensitivity of the sensors is analytically estimated. The developed calibration procedure is validated with synthetic data mimicking a real scenario.

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  • 1. M. Hämäläinen R. Hari J. Knuutila and O. Lounasmaa Magnetoencephalography: theory instrumentation and applications to non-invasive studies of the working human brain Reviews of Modern Physics vol. 65 pp. 413–498 1993.

  • 2. C. Del Gratta V. Pizzella F. Tecchio and G. Romani Magnetoencephalography-a noninvasive brain imaging method with 1 ms time resolution Reports on Progress in Physics vol. 64 pp. 1759–1814 2001.

  • 3. C. P. Foley M. N. Keene H. J. M. ter Brake and J. Vrba Squid system issues. Wiley-VCH Verlag GmbH & Co KGaA Weinheim 2004.

  • 4. A. Bruno and P. C. Ribeiro Spatial fourier calibration method for multichannel squid magnetometers Review of scientific instruments vol. 62 pp. 1005–1009 1991.

  • 5. J. R. Kraus A. Matlacov P. Volegov M. Espy K. Maharajh and E. Flynn Source localization precision of the superconducting imaging-surface meg system Biomedizinische Technik/Biomedical Engineering vol. 46 pp. 38–40 2001.

  • 6. A. Pasquarelli R. Rossi M. D. Melis L-Marzetti A. Trebeschi H. Muller and S. Ernè Argo 500: Operation of a helmet vector-meg Neurology and Clinical Neurophysiology vol. 97 p. : 16012682 2004.

  • 7. A. Pasquarelli R. Rossi M. D. Melis L-Marzetti A. Trebeschi H. Muller and S. Ernè Calibration of a vector-meg helmet system Neurology and Clinical Neurophysiology vol. 94 p. : 16012682 2004.

  • 8. F. Chella F. Zappasodi S. D. Penna and V. Pizzella Calibration of a multichannel MEG system based on the Signal Space Separation method Physics in Medicine and Biology vol. 57 pp. 4855– 4870 2012.

  • 9. C. Wienbruch Meg-calibration-v. 2.0 tech. rep. Department of Psychology University of Konstanz Germany 2013.

  • 10. A. V. S. Rombetto C. Granata and M. Russo Multichannel system based on a high sensitivity superconductive sensor for magnetoencephalography Sensors vol. 14 (7) pp. 12114–12126 2014.

  • 11. J. A. Nelder and R. Mead A simplex method for function minimization Computer Journal vol. 7 (4) pp. 308–313 1965.

  • 12. R. O’Neill Function minimization using a simplex procedure Journal of the Royal Statistical Society. Series C (Applied Statistics) vol. 20 (3) pp. 338–345 1971.

  • 13. S. Baillet J. Mosher and R. Leahy Electromagnetic brain mapping Signal Processing Magazine IEEE vol. 18 pp. 14–30 2001.

  • 14. W. Kabsch A solution for the best rotation to relate two sets of vectors Acta Crystallographica vol. 32 pp. 922–923 1976.

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CiteScore 2018: 0.95

SCImago Journal Rank (SJR) 2018: 0.324
Source Normalized Impact per Paper (SNIP) 2018: 0.73

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