TMS PHANTOMS FOR INVESTIGATING MULTIMODAL NEUROMODULATION PROCEDURES

Abstract

Evidence suggests that combining deep brain stimulation (DBS) and transcranial magnetic stimulation (TMS) is potentially unsafe for certain TMS target locations, though TMS can alleviate several DBS-resistant PD symptoms such as speech impairment, freezing of gait, and dysphagia. Addressing this issue, head phantoms designed for TMS with embedded electric field (E-field) triaxial dipole probes (TDPs) are used to investigate a tunable magnetic shield that can protect implants from periphery E-fields and focalize magnetic fields. Through segmentation of MRI files, 3D printing, and injection molding of CNT-PDMS conductive composites, anatomical head phantoms are created. Anchoring TDPs to clinically relevant regions in the brain (M1, DLPFC, ACC, etc.) creates a precise coordinate system for mapping E-fields. Measurements of E-fields in rat phantoms have been cross validated with Sim4Life simulations with less than 5% error and used to evaluate novel TMS coil performance. High permeability composites were found to attenuate up to 30% of low TMS fields before saturation. High conductive magnetic shields show reduced DBS current induction by 40%. Investigation of shield apertures for focal stimulation reveals the possibility of attenuating over 80% of peripheral E-fields at the cost of E-max. These findings demonstrate the feasibility of creating a multimodal TMS/ DBS treatment, without risking patient safety or device performance, reliant on an effective balance between attenuation and stimulation.