Hybrid Transcranial Magnetic Stimulation and Deep Brain Stimulation in the Presence of an Implantable Pulse Generator

Transcranial magnetic stimulation (TMS) has been shown to improve speech impairment in Parkinson's disease (PD) patients. Most PD patients undergo deep brain stimulation (DBS) implantation to improve their motor function prior to the development of speech impairment. Therefore, the potential for TMS treatment must take into account the DBS probes' high conductivity, potentially causing excess stimulation. Prior research regarding this phenomenon is highly conflicting and needs investigation. This study reports electromagnetic interference using a highly accurate finite element analysis approach to determine the electric field distribution in patients with DBS probes undergoing TMS therapy. Additionally, we tested various coil orientations and coil models to fully examine the extent that TMS affects DBS. We considered accurate DBS geometry by creating high-resolution models of Medtronic 3389 DBS, including an implantable pulse generator (IPG) and multiple loops at the exit point of the cranium, which previous studies lack. By studying the induced current in the DBS leads, we determined that the combination of TMS and DBS varies in safety relative to its coil orientation and coil type. Specifically, the quadruple butterfly coil (QBC) targeted at the lateral motor cortex did not induce unsafe levels of currents in the DBS leads even at 100% of the maximum stimulator output.