Jun 7, 2016

Functionalized anatomical models for EM-neuron interaction modeling

Esra Neufeld, Antonino M. Cassara, Hazael Montanaro, and Niels Kuster, Physics in Medicine and Biology, Volume 61, Issue 12, 4390–4401, online May 25, 2016

The understanding of interactions between electromagnetic (EM) fields and nerves is crucial in contexts ranging from therapeutic neurostimulation to low frequency EM exposure safety. To properly consider the impact of induced field inhomogeneity on non-linear neuronal dynamics in vivo, coupled EM-neuronal dynamics modeling is required. For that purpose, novel functionalized computable human phantoms have been developed, of which the implementation and systematic verification of the integrated anisotropic quasi-static EM solver and neuronal dynamics modeling functionality, based on the method of manufactured solutions and numerical reference data, is described. Electric and magnetic stimulation of the ulnar and sciatic nerves were modeled to help understanding a range of controversial issues related to the magnitude and optimal determination of strength-duration (SD) time constants. The results indicate the importance of considering the stimulation-specific inhomogeneous field distributions (especially at tissue interfaces), realistic models of non-linear neuronal dynamics, very short pulses, and suitable SD extrapolation models. These results and the functionalized computable phantom will influence and support the development of safe and effective neuroprosthetic devices and novel electroceuticals, and furthermore assist the evaluation of existing low frequency exposure standards for the entire population under all exposure conditions.

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

  • The development and verification of computable, functionalized anatomical models within the Virtual Population (ViP) for the investigation of coupled EM-neuronal dynamics is described
  • An anisotropic LF FEM solver has been developed and extensively verified for correct handling of discontinuities, anisotropy, inhomogeneity, and boundary conditions
  • The integration of NEURON permits modeling of neurons with complex morphologies and channel dynamics
  • The functionalized ViP models can be used to study the combined effect of inhomogeneous in vivo fields and detailed neuronal dynamics
  • Application of the functionalized ViP models provides insight into factors that explain conflicting time-constant measurement reports and demonstrate the need for coupled EM-neuronal dynamics simulations, realistic electrophysiological models, and consistent approaches to extract time-constants from strength-duration curves