Improvement in Efficiency of Transcranial Magnetic Stimulator Coil by Combination of Iron Core Plates Laminated in Different Directions

Recent studies have revealed that transcranial magnetic stimulation (TMS) has therapeutic effects for various neurological and psychiatric diseases, such as neuropathic pain and depression. However, since TMS requires a high voltage and a large current, the TMS coil heats quickly, and this prevents doctors from treating patients for prolonged periods with high-frequency stimulation. We have previously proposed a centered-eccentric figure-8 coil that could stimulate the motor cortex with lower current compared with conventional figure-8 coils. However, the enhancement in the efficiency of this coil was not sufficient. In this paper, to enhance the efficiency of the centered-eccentric figure-8 coil, we propose a new coil with a laminated iron core plate, and evaluate its effect on stimulation intensity based on finite-element method simulations. We performed the simulations for the following scenarios: 1) no iron core plate; 2) a non-laminated iron core plate; 3) a vertically laminated iron core plate; 4) a horizontally laminated iron core plate; and 5) a combination of vertically and horizontally laminated iron core plates. The results show that the combination of the iron core plates laminated in different directions yielded the best improvement in stimulation intensity, and the power of such a coil would be 2.8 times that of the coil with no plate. Thus, the current applied to the coil can be considerably reduced by using a combination of laminated iron core plate.