Comparative Study of a New Coil Design With Traditional Shielded Figure-of-Eight Coil for Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) is a non-invasive neuro-stimulation based on the principle of electromagnetic induction that uses brief, strong magnetic pulses of electric current delivered to a coil placed on the subject's head to induce an electric field in the brain. This electric field could stimulate and modulate neural activity. Induced E-field inside brain generated by repetitive TMS (rTMS) can produce changes in neural activity that extends beyond the period of stimulation. Therefore, rTMS can be used as a probe for exploring higher brain functions and as potential treatment technique for psychiatric and neurological disorders. However, based on the chosen shape of the excitation coil, there exists a tradeoff between the excitation focality in the brain and the depth to which the field penetrates. In this paper, a new design of TMS coil is proposed to enhance the performance of the traditional figure-of-eight (FOE) coil. 3-D finite-element method has been used to simulate and compare the electric field induced inside the model of a human brain under the influence of both coil designs. An experimental verification was then followed to validate the advantages of the proposed coil design over the classic FOE coil.