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Development of Inverse Problem Analysis System in Electromagnetics

Article of Honda R&D Technical Review Vol.26 No.1

Summary

An inverse problem analysis system for electromagnetic fields, for use in the field of brain-machine interfaces (BMI), has been developed. In the conventional technique, a spherical approximation of the human head is used for the calculation of the electromagnetic field in the brain. The spherical approximation presents the issues that the shape and electromagnetic properties of the human head cannot be considered in the calculations, and that the currents normal to the surface of the sphere cannot be detected. In order to address these issues, we used the boundary element method (BEM) as a numerical method, to calculate the electromagnetic field, in addition to developing the mesh model and mesh generation method that were essential to the calculations. We employed a minimum-variance spatial filter as the method for inverse problems and applied a sub-grid technique to minimize the increase in calculation time of the numerical method. We verified the effectiveness of the method using a numerical simulation problem to reconstruct the hypothetical electric current sources in the brain. The results showed that the system was able to analyze inverse problems with consideration of the shape and electromagnetic properties of the tissues of the human head.

Reference

(1) Okabe, T., Yamada, K., Kimura, M., Toda, A., Sato, M., Yamashita, O., Takeda, Y., Kawato, M.: Brain Machine Interface Technology Enabling Control of Machine by Human Thought Alone, Honda R&D Technical Review, Vol. 22, No. 2, p. 93-100
(2) Taubin, G.: A signal processing approach to fair surface design, SIGGRAPH ’95 proceedings of the 22nd annual conference on Computer graphics and interactive techniques, p. 351-358, (1995)
(3) Sarvas, J.: Basic mathematical and electromagnetic concepts of the biomagnetic inverse problem, Phys. Med. Biol., Vol. 32, No. 1, p. 11-22, (1987)
(4) Capon, J.: High-resolution frequency wavenumber spectrum analysis, Proc. IEEE, Vol. 57, p. 1408-1419, (1969)
(5) Kumihashi, I., Sekihara, K.: Array-gain constraint minimum-norm spatial filter with recursively updated gram matrix for biomagnetic source imaging, IEEE Trans. Biomed. Eng., Vol. 57, p. 1358-1365, (2010)

Author (organization or company)

Masatoshi HARUMATSU(Fundamental Technology Research Center)、Katsuya YASHIRO(Fundamental Technology Research Center)、Kensuke SEKIHARA(Tokyo Metropolitan University)

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