Current Density Distribution Under Surface Electrode on Posterior Tibial Nerve Electrical Stimulation

Electrical stimulation on the posterior tibial nerve is commonly used in the measurement of somatosensory evoked potential (SEP). To improve the efficiency of stimulation, the potential field and current density distributions under the surface electrodes were simulated with a three layer theoretical model. The mirror method was used to analyze the potential field of point charge. Integration of the field and the stimulus area provide the potential field for one surface electric pole. Potential field distribution of the bipolar electrodes was calculated by superimposition of two unipolar fields. Finally, the current density distribution was calculated by Laplace equation. An analytical solution of the potential field was obtained; thereafter the numerical solution of the current density distribution was calculated. The potential field and current density distribution were simulated by 2-D plot. From the model and simulation, the potential and current density distributions were not found to be evenly distributed under transcutaneous stimulation electrode and the maximum current density is located under the poles. The result suggests that bipolar stimulator should be applied axially along the stimulated nerve course.