Evaluation of RF interactions between a 3T birdcage transmit coil and transcranial magnetic stimulation coils using a realistically shaped head phantom

Lucia I. Navarro de Lara*, Laleh Golestanirad, Sergey N. Makarov, Jason P. Stockmann, Lawrence L. Wald, Aapo Nummenmaa

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Purpose: Multichannel transcranial magnetic stimulation (TMS)1 is an emerging technology that allows multiple sites to be stimulated simultaneously or sequentially under electronic control without movement of the coils. A multichannel TMS/MRI head coil array for 3 Tesla is currently under development to mitigate challenges of concurrent TMS/fMRI as well as enable potential new applications. The influence of the multichannel TMS system on the MR image quality and safety must be carefully investigated. Methods: A standard birdcage volume coil for 3 Tesla systems was simulated using a commercial numerical electromagnetic solver. Two setups, consisting of 1) a MR-compatible TMS coil, and 2) a 3-axis TMS coil array, were simulated to quantify changes in the transmit field (Formula presented.) and the SAR. A realistically shaped homogeneous head model was used in the computations. Results: The stimulation coils produced enhancements and attenuations on the transmit field with effects greater than 5% up to 2.4 cm and 3.3 cm under the scalp for the MR-compatible TMS coil and 3-axis TMS coil array, respectively. The 10 g-SAR distribution did not change significantly in either of the cases; however, the nominal SAR maximum locus was shifted between existing hot spots. Conclusion: The simulated (Formula presented.) variations found near the TMS coils indicate the possibility of inducing sequence-dependent image artefacts predominatly limited to the vicinity of the coil(s). However, we conclude that neither the MR-compatible commercial TMS coil nor the 3-axis TMS coil array siginificantly elevate SAR in the head or neck beyond accepted safety limits.

Original languageEnglish (US)
Pages (from-to)1061-1075
Number of pages15
JournalMagnetic resonance in medicine
Volume84
Issue number2
DOIs
StatePublished - Aug 1 2020

Keywords

  • B 1 +
  • SAR
  • TMS
  • birdcage coil
  • fMRI
  • multichannel TMS

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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