THE INFLUENCE OF BOUNDARY-ELEMENT DISCRETIZATION ON THE FORWARD AND INVERSE PROBLEM IN ELECTROENCEPHALOGRAPHY AND MAGNETOENCEPHALOGRAPHY

Modelling in magnetoencephalography (MEG) and electroencephalography ( EEG) is increasingly based on the boundary element method (BEM). We qu antify the influence of boundary element discretization on the neuroma gnetic and neuroelectric forward and inverse problem for different dip ole depths, brain regions and the quasispherical correction. In partic ular we derive standards for the general use of BEM models in MEG/EEG source localization. For this purpose simulation with single current d ipoles, and source reconstructions from somatosensory evoked potential s and magnetic fields were employed. It was found that both local and global discretization influence source reconstruction. Only at a minim um triangle side length of 10 mm was it possible to achieve stable res ults for MEG and EEG. In order to obtain acceptable errors within the stable region, the ratio of dipole depth to triangle side length must not be less than 0.5. The results obtained from a comparison of the di fferent brain regions indicate that the similarity to spherical geomet ry might well have an influence on the estimated dipole location, but not so much on its strength. Source reconstruction employing quasisphe rical correction was found to be the most stable, in particular in the case of coarse BEM discretization.