Volume conductor effects on the spatial resolution of magnetic fields and electric potentials from gastrointestinal electrical activity

An analysis of the relative capabilities of methods for magnetic and electr ic detection of gastrointestinal electrical activity is presented. The mode l employed is the first Volume conductor model for magnetic fields from GEA to appear in the literature. A mathematical model is introduced for the el ectric potential and magnetic field from intestinal electrical activity in terms of the spatial filters that relate the bioelectric sources with the e xternal magnetic fields and potentials. The forward spatial filters are low -pass functions of spatial frequency, so more superficial external fields a nd potentials contain less spatial information than fields and potentials n ear the source. Inverse spatial filters, which are reciprocals of the forwa rd filters, are high-pass functions and must be regularised by windowing. B ecause of the conductivity discontinuities introduced by low-conductivity f at layers in the abdomen, the electric potentials recorded outside these la yers required more regularisation than the magnetic fields, and thus, the s patial resolution of the magnetic fields from intestinal electrical activit y is higher than the spatial resolution of the external potentials. In this study, two smooth muscle sources separated by 5cm were adequately resolved magnetically, but not resolved electrically Thus, sources are more accurat ely localized and imaged using magnetic measurements than using measurement s of electric potential.