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07/06/2016

Investigation of assumptions underlying current safety guidelines on EM-induced nerve stimulation

Esra Neufeld, Ioannis Vogiatzis Oikonomidis, Maria Ida Iacono, Leonardo M. Angelone, Wolfgang Kainz, and Niels Kuster, Physics in Medicine and Biology, Volume 61, Issue 12, pp. 4466–4478, online May 2016

An intricate network of a variety of nerves is embedded within the complex anatomy of the human body. Although nerves are shielded from unwanted excitation, they can still be stimulated by external electromagnetic sources that induce strongly non-uniform field distributions. Current exposure safety standards designed to limit unwanted nerve stimulation are based on a series of explicit and implicit assumptions and simplifications. This paper demonstrates the applicability of functionalized anatomical phantoms with integrated coupled electromagnetic and neuronal dynamics solvers for investigating the impact of magnetic resonance exposure on nerve excitation within the full complexity of the human anatomy. The impact of neuronal dynamics models, temperature and local hot-spots, nerve trajectory and potential smoothing, anatomical inhomogeneity, and pulse duration on nerve stimulation was evaluated. As a result, multiple assumptions underlying current safety standards are questioned. It is demonstrated that coupled EM-neuronal dynamics modeling involving realistic anatomies is valuable to establish conservative safety criteria.

The scientific and technical impact of the study can be summarized as:

  • Computable, functionalized anatomical phantoms enriched with integrated nerve trajectory and neuronal dynamics models were used to investigate low-frequency MRI exposure safety
  • The full anatomical complexity of the Virtual Population ViP3.0 models enhanced with electrophysiologically detailed functionalization allow critical investigation of assumptions underlying current safety standards
  • Application of coupled EM-neuronal dynamics simulations in the ViP3.0 models permits study of the impact of temperature and local hot-spots, anatomical inhomogeneity, pulse duration, as well as nerve trajectory
  • The functionalized ViP3.0 models were demonstrated to be a valuable tool for safety assessments and investigations of stimulation mechanisms

 

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