Safety evaluation of a new setup for transcranial electric stimulation during magnetic resonance imaging

Fróði Gregersen, Cihan Göksu, Gregor Schaefers, Rong Xue, Axel Thielscher, Lars G. Hanson*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

Background: Transcranial electric stimulation during MR imaging can introduce safety issues due to coupling of the RF field with the stimulation electrodes and leads. Objective: To optimize the stimulation setup for MR current density imaging (MRCDI) and increase maximum stimulation current, a new low-conductivity (σ = 29.4 S/m) lead wire is designed and tested. Method: The antenna effect was simulated to investigate the effect of lead conductivity. Subsequently, specific absorption rate (SAR) simulations for realistic lead configurations with low-conductivity leads and two electrode types were performed at 128 MHz and 298 MHz being the Larmor frequencies of protons at 3T and 7T. Temperature measurements were performed during MRI using high power deposition sequences to ensure that the electrodes comply with MRI temperature regulations. Results: The antenna effect was found for copper leads at ¼ RF wavelength and could be reliably eliminated using low-conductivity leads. Realistic lead configurations increased the head SAR and the local head SAR at the electrodes only minimally. The highest temperatures were measured on the rings of center-surround electrodes, while circular electrodes showed little heating. No temperature increase above the safety limit of 39 °C was observed. Conclusion: Coupling to the RF field can be reliably prevented by low-conductivity leads, enabling cable paths optimal for MRCDI. Compared to commercial copper leads with safety resistors, the low-conductivity leads had lower total impedance, enabling the application of higher currents without changing stimulator design. Attention must be paid to electrode pads.

Original languageEnglish
JournalBrain Stimulation
Volume14
Issue number3
Pages (from-to)488-497
ISSN1935-861X
DOIs
Publication statusPublished - 2021

Bibliographical note

Funding Information:
This study was supported by the Lundbeck Foundation (grants R313-2019-622 and R244-2017-196 to AT and R288-2018-236 to CG ), the Chinese National Major Scientific Equipment R&D Project (grant ZDYZ2010-2 ) and a PhD stipend of the Sino-Danish Center for Education and Research to FG. The authors thank Zuo Zhentao, Hasan Hüseyin Eroğlu, Vincent Boer, and Esben Thade Petersen for kind technical help.

Keywords

  • MR current Density imaging
  • MR electrical Impedance tomography
  • Safety
  • Transcranial electric stimulation

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