ABSTRACT
The representations of the intracellular electric current of the active cell populations in the brain based on the recorded magnetic fields are called magnetic source images. For accurate interpretation of the measured data it is necessary to calculate the magnetic fields outside a head model for a known source distribution. In this study, the theory governing the behavior of magnetic field due to current sources in a piecewise conductive body is introduced, and the basic properties are discussed. To localize the sources of the magnetic fields it is essential to develop head models that incorporate the correct geometry and electrical properties of the head. This chapter presents two numerical approaches to develop realistic models: (a) the boundary element method (BEM) and (b) the finite element method (FEM). In the FEM formulation isoparametric quadratic elements are used. In BEM formulations both planar and curved triangles are used. On planar elements the potential function varies linearly whereas formulations for curved triangles allow quadratic or cubic variation for both the geometry and the potential function. The accuracy in solutions is explored for a tan-gential dipole source located at different depths in a concentric spherical shell model of the head. The relative difference measures are calculated, and it is shown that the use of higher order elements enhances accuracy in the forward problem solutions.
