Effects of Coil Parameters on the Stimulated Area by Transcranial Magnetic Stimulation

In this study, we investigate the relationships between the eddy current density and the coil configuration of transcranial magnetic stimulation (TMS). The aim of this study is to determine the coil parameters such as the radius of the coil and the bending angle of the coil to stimulate specified area such as the dorsolateral prefrontal cortex (DLPFC). We used a realistic 3-D human head model with inhomogeneous conductivity to obtain accurate eddy current distributions. In the TMS model, eddy current distributions were obtained for figure-eight coils with radius of 30, 40 and 50 mm, and a bending angle of the coil changed from 0 to 30 degrees. Computer simulations show that the maximum value of the eddy current increases linearly with the increase of the radius and the bending-angle of the coil. The maximum eddy current density was 87.6 A/m² under the case where the bending-angle was 30 degrees and the radius was 50 mm. The stimulated area increased with the increase of the radius and bending-angle of the coil. It is possible to determine coil parameters to stimulate target area appropriately.