The Effects of Using Ferromagnetic Core and Shield on Deep TMS Systems

Non-invasive deep transcranial magnetic stimulation (TMS) is a promising technique to treat many neurological conditions like Alzheimer’s disease. Adequate stimulation performance in the deep region of the brain is considered as one of the main challenges of current TMS coils. In this study, the effects of modifying the coil by adding a magnetic core and shield on the induced field’s strength, focality, decay rate, and safety are investigated. The induced electric field in a realistic human head phantom is calculated using the finite element methods (FEM) based electromagnetic tool, Sim4life, and the results are compared for different scenarios. Simulation results show that using ferromagnetic core and shield increase the field intensity and enhance the focality, with no evidence of improving the field’s decay rate. Additionally, employing iron shield around the coil can significantly reduce the field on the operator’s side. The recommendation of using the magnetic core and shield in deep brain stimulation is for large coils that can enhance the field’s intensity, focality, safety, and power efficiency without badly affecting the field’s attenuation inside the head.