Investigation of current densities produced by surface electrodes using finite element modeling and current density imaging

Designers of gel-type surface electrodes, used in medical applications such as pain relief and neuromuscular stimulation, require a more thorough understanding of current pathways in tissue in order to design more effective electrical stimulation systems. To investigate these pathways, a finite element model (FEM) was used to compute current density distributions produced by an electrode placed on the surface of a homogeneous, tissue-mimicking gel slab. The gel slab phantom was constructed and the current densities were measured using a recently developed technique called current density imaging (CDI). CDI uses the phase data produced by magnetic resonance imaging (MRI) as a measure of the magnetic fields produced by the externally applied current. The results of the FEM simulation and CDI measurements compare well. CDI has several potential advantages over conventional FEM techniques including: no requirement for knowledge of local tissue conductivities, low and constant computational overhead regardless of tissue complexity, and the potential to perform in-vivo measurements.