Coil Size and Current Pulse Optimization through Multi-Scale Modeling for Repetitive Transcranial Magnetic Stimulation (rTMS)

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive treatment modality utilized to treat several mental disorders including drug resistant depression, PTSD, and autism. In rTMS treatment, rapidly varying electric current is passed through a coil positioned in the vicinity of the skull. This creates a rapidly changing magnetic field, which in turn induces an electric field in the cortex, influencing neural activity. Although great progress has been made in utilizing rTMS in the past few years, the exact underlying mechanisms and optimal operating parameters are still uncertain. As a result, investigating the effects of treatment parameters on stimulation efficacy is critical. In this work we investigate the effect of rTMS system parameters on the threshold of neural stimulation, with the goal of creating a compact battery-powered rTMS system to increase treatment accessibility. These parameters include coil properties such as size and shape, as well as electric current properties such as pulse shape and pulse width. A newly developed modeling toolbox called Neural Modeling for TMS (NeMo-TMS) is utilized. The control tools added to NeMo-TMS by our team allow for finding the stimulation threshold for several pulse shapes and widths, as well as coil sizes. The simulation results can be a guideline for the coil size and optimum current pulse shape and width in a miniaturized rTMS system.