Simulation of the three-dimensional electrical field in the course of functional electrical stimulation

Optimization of stimulation parameters as well as shape and positioning of electrodes are important questions in functional electrical stimulation (FES) of paraplegic patients. For that reason a MATLAB tool, called FES-FIELD, modeling the three-dimensional electric field in the human body, has been developed to calculate the electric field in a region of interest. The simulation tool provides a graphic user interface. In case of denervation of the lower extremities, an important target muscle is the m. quadriceps femoris. The electrical potential distribution along its fibers is representative for its functional activation. For this special application, the human thigh stimulated by skin electrodes was modeled. The simulation process was done in 5 steps: reading the geometric information of the thigh from 50 computed tomographic slices, segmentation in tissue types by pixel value and definition of each conductivity, selection of electrode geometry and positioning, calculating the electric field iteratively by solving the system of linear equations, and visualization of the solution by equipotential lines in either cross or length sections of the thigh.