The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Numerical Modeling in Electro- and Magnetoencephalography

I. Oğuz Tanzer

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 13th of March, 2006, at 12 noon.

Overview in PDF format (ISBN 951-22-8091-4)   [2975 KB]
Dissertation is also available in print (ISBN 951-22-8090-6)

Abstract

This Thesis concerns the application of two numerical methods, Boundary Element Method (BEM) and Finite Element Method (FEM) to forward problem solution of bioelectromagnetic source localization in the brain. The aim is to improve the accuracy of the forward problem solution in estimating the electrical activity of the human brain from electric and magnetic field measurements outside the head.

Electro- and magnetoencephalography (EEG, MEG) are the most important tools enabling us to gather knowledge about the human brain non-invasively. This task is alternatively named brain mapping. An important step in brain mapping is determining from where the brain signals originate. Using appropriate mathematical models, a localization of the sources of measured signals can be performed. A general motivation of this work was the fact that source localization accuracy can be improved by solving the forward problem with higher accuracy.

In BEM studies, accurate representation of model geometry using higher order elements improves the solution of the forward problem. In FEM, complex conductivity information can be incorporated into numerical model. Using Whitney-type finite elements instead of using singular sources such as point dipoles, primary and volume currents are represented as continuous sources. With comparison to analytical solutions available in simple geometries such as sphere, the studied numerical methods show improvements in the forward problem solution of bioelectromagnetic source imaging.

This thesis consists of an overview and of the following 6 publications:

  1. Gençer N. G., Tanzer I. O., Özdemir K., Acar C. and Sungur M. (1998). State of art in realistic head modeling for electromagnetic source imaging of the human brain, Elektrik, 6: 167-182.
  2. Gençer N. G. and Tanzer I. O. (1999). Forward problem solution of electromagnetic source imaging using a new BEM formulation with high order elements, Physics in Medicine and Biology, 44: 2275-2287.
  3. Gençer N. G., Acar C. E. and Tanzer I. O. (2003). Forward problem solution of magnetic source imaging, Magnetic Source Imaging of the Human Brain, Eds: Zhong-Lin Lu, Lloyd Kaufman, Lawrence Erlbaum Associates Inc., ISBN 0805845119, 77-100.
  4. Tanzer I. O., Järvenpää S., Nenonen J. and Somersalo E. (2003). Effect of potential approximation on linear inversion from surface potential and magnetic field, Biomedizinische Technik, 48: 254-257.
  5. Tanzer I. O., Järvenpää S., Nenonen J. and Somersalo E. (2005). Representation of bioelectric current sources using Whitney elements in the finite element method, Physics in Medicine and Biology, 50: 3023-3039.
  6. Tanzer I. O., Järvenpää S. and Somersalo E. (2005). An alternative formulation to represent bioelectric current sources using Whitney elements, Helsinki University of Technology publications in engineering physics, Report TKK-F-A840.

Keywords: EEG, MEG, boundary element method, finite element method, forward problem

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© 2006 Helsinki University of Technology

Last update 2011-05-26