FEM-based determination of optimum current distribution in transcranial magnetic stimulation as an alternative to electroconvulsive therapy

In this study, we investigated dependences of the current distribution in transcranial magnetic stimulation (TMS) on coil current intensity, coil diameter, and coil position, and compared the current distribution with that of electroconvulsive therapy (ECT). The head model consisted of 4-mm finite elements. In the ECT model, a voltage of 100 V was applied between a pair of electrodes place on the tempora. In the TMS model, eddy current distributions were obtained for figure-eight coils with diameters of 50, 75, and 100 mm, and coil positions varied from the vertex to the forehead. The difference in current distributions in ECT and TMS decreased with the coil position approaching to the forehead. The coil of 100-mm diameter gave the minimum difference at a coil current of 87 kA. The difference decreased with an increase in the coil diameter.