Goldie R Boone MS, Presenter: Nothing to Disclose

Geoffrey D. Clarke PhD, Abstract Co-Author: Nothing to Disclose

Transcranial magnetic stimulation (TMS) uses electromagnetic induction to generate weak electric currents by application of rapidly changing magnetic fields to depolarize or hyperpolarize neurons in the brain. The potential for induced heating of brain tissues located near bilaterally implanted deep brain stimulation (DBS) electrodes during application of single pulse and repetitively pulsed TMS was investigated. This study provides empirical evidence for the “reasonable assurance of safety” in the FDA’s classification of TMS as a Class II (special controls) device.

TMS was conducted using the MagPro R30 system (MagVenture, Denmark) with a liquid cooled butterfly coil (model Cool-B65). TMS-induced heating was measured using a proprietary phantom and a clinical/research stimulation protocol. Fiber optic thermometry probes acquired real-time temperature measurements of the induced heating at the surface of the metallic DBS electrodes during TMS. The three specific aims of this study were to evaluate the 1) spatially localized temperature increase, 2) spatially localized specific absorption rate (SAR), and 3) the average head SAR in the phantom in the absence and presence of the DBS implant over a 6 minute averaging period in saline and gelled-saline solutions at stimulation frequencies of 1 and 5 Hz. The differences in the average temperatures in the presence and absence of bilateral DBS implants were analyzed by ANOVA (p = 0.05, power = 0.80) with Bonferroni correction.

In the clinical/research stimulation orientation, no evidence of induced heating effects was observed above the thermal noise. However, stimulation of the lead loops at 5 Hz in gelled saline at a distance of 0.5 cm from the coil’s surface and peak intensity region resulted in temperatures that tripled the spatially localized temperature limit and SAR values that doubled the spatially localized SAR limit. TMS-induced heating effects of this nature may result in localized tissue damage.

The observations in this research study support the use of repetitive TMS of patients with a bilateral DBS device implant provided prior knowledge is used to guide surgical lead configuration and careful coil placement during stimulation.

The data support the use of repetitive TMS as a safe adjuvant therapy to surgery and pharmaceuticals in the treatment of neurological movement and major depressive disorders.

Boone, G, Clarke, G, Transcranial Magnetic Stimulation-Induced Heating of Deep Brain Stimulation Implants: An Empirical Specific Absorption Rate Evaluation Using a Tissue Equivalent Phantom.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13017551.html