Enhancement of Penetration Depth and Focality in Transcranial Magnetic Stimulation Using Combined X-halo and Annulus Sector Coils

Abstract

Transcranial magnetic stimulation (TMS), a non-invasive therapeutic method, has attracted considerable interest for its potential in addressing diverse neurological disorders. Several types of TMS coils have been proposed to enhance the stimulating characteristics such as penetration depth and focality of the induced electric field. In this study, the X-halo and annulus sector coils are proposed to address the trade-off between penetration depth and focality of electric field. The stimulating characteristics of the proposed coils are simulated using a finite element method for the conductive head model. It is demonstrated that penetration depth and focality can be controlled by the relative position of the annulus sector coils and adjusting the current ratio between the two coils. A comparison with previously reported coils indicates that the proposed coils can achieve deeper penetration depth for the same stimulating area, suggesting an improvement in the trade-off between penetration depth and focality. The simulation results were validated by the measurement of the magnetic and electric field distribution in air generated by the fabricated coils.