THE INFLUENCE OF INHOMOGENEOUS VOLUME CONDUCTOR MODELS ON THE ECG ANDTHE MCG

We investigated the influence of human body inhomogeneities such as th e lungs, blood masses and the skeletal muscle layer on the electrical body surface potential and the magnetic held. The surface potentials a nd magnetic fields are calculated using a boundary element method. As a rule the blood masses have a large influence on both potential and m agnetic held amplitude as well as on the potential and magnetic field map orientation, but the influence on the topology of the map is less in the electric case than in the magnetic case. The single-dipole reco nstruction was applied to estimate the error caused by neglecting inne r inhomogeneities in source localization. The neglect of lungs and blo od masses results in a localization error of less than 1 cm in the ele ctric case but more than 1 cm for deep sources at the posterior side o f the heart in the magnetic case. We tried to assess the influence of the skeletal muscle layer by both an analytical two-layered anisotropi c half-space model and the torso extension method. The skeletal muscle layer causes a smoothing effect on the electrical surface potential a nd to a lesser,extent on the magnetic held, leading to an overestimati on of the actual source depth of about 1-2 cm. In principle this can b e reduced by taking data from all over the thoracic surface. We design ed experiments for simultaneous measurement of body surface potential and-extracorporeal magnetic field from the same subject. The evaluatio n of data from two patients showing Wolff-Parkinson-White syndrome has shown that localization results from electric potential data and magn etocardiographic data are consistent.