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Effective electric fields along realistic DTI-based neural trajectories for modelling the stimulation mechanisms of TMS

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Abstract
In transcranial magnetic stimulation (TMS), an applied alternating magnetic field induces an electric field in the brain that can interact with the neural system. It is generally assumed that this induced electric field is the crucial effect exciting a certain region of the brain. More specifically, it is the component of this field parallel to the neuron's local orientation, the so-called effective electric field, that can initiate neuronal stimulation. Deeper insights on the stimulation mechanisms can be acquired through extensive TMS modelling. Most models study simple representations of neurons with assumed geometries, whereas we embed realistic neural trajectories computed using tractography based on diffusion tensor images. This way of modelling ensures a more accurate spatial distribution of the effective electric field that is in addition patient and case specific. The case study of this paper focuses on the single pulse stimulation of the left primary motor cortex with a standard figure-of-eight coil. Including realistic neural geometry in the model demonstrates the strong and localized variations of the effective electric field between the tracts themselves and along them due to the interplay of factors such as the tract's position and orientation in relation to the TMS coil, the neural trajectory and its course along the white and grey matter interface. Furthermore, the influence of changes in the coil orientation is studied. Investigating the impact of tissue anisotropy confirms that its contribution is not negligible. Moreover, assuming isotropic tissues lead to errors of the same size as rotating or tilting the coil with 10 degrees. In contrast, the model proves to be less sensitive towards the not well-known tissue conductivity values.
Keywords
LIMITATIONS, diffusion tensor imaging (DTI), transcranial magnetic stimulation (TMS), primary motor cortex (M1), INDEPENDENT IMPEDANCE METHOD, HUMAN MOTOR CORTEX, BIOLOGICAL TISSUES, FIBER, TRACTOGRAPHY, DIFFUSION TENSOR MRI, HUMAN BRAIN, tractography, effective electric field, DEPRESSION, TRANSCRANIAL MAGNETIC STIMULATION

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Citation

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MLA
De Geeter, Nele et al. “Effective Electric Fields Along Realistic DTI-based Neural Trajectories for Modelling the Stimulation Mechanisms of TMS.” PHYSICS IN MEDICINE AND BIOLOGY 60.2 (2014): 453–471. Print.
APA
De Geeter, N., Crevecoeur, G., Leemans, A., & Dupré, L. (2014). Effective electric fields along realistic DTI-based neural trajectories for modelling the stimulation mechanisms of TMS. PHYSICS IN MEDICINE AND BIOLOGY, 60(2), 453–471.
Chicago author-date
De Geeter, Nele, Guillaume Crevecoeur, Alexander Leemans, and Luc Dupré. 2014. “Effective Electric Fields Along Realistic DTI-based Neural Trajectories for Modelling the Stimulation Mechanisms of TMS.” Physics in Medicine and Biology 60 (2): 453–471.
Chicago author-date (all authors)
De Geeter, Nele, Guillaume Crevecoeur, Alexander Leemans, and Luc Dupré. 2014. “Effective Electric Fields Along Realistic DTI-based Neural Trajectories for Modelling the Stimulation Mechanisms of TMS.” Physics in Medicine and Biology 60 (2): 453–471.
Vancouver
1.
De Geeter N, Crevecoeur G, Leemans A, Dupré L. Effective electric fields along realistic DTI-based neural trajectories for modelling the stimulation mechanisms of TMS. PHYSICS IN MEDICINE AND BIOLOGY. 2014;60(2):453–71.
IEEE
[1]
N. De Geeter, G. Crevecoeur, A. Leemans, and L. Dupré, “Effective electric fields along realistic DTI-based neural trajectories for modelling the stimulation mechanisms of TMS,” PHYSICS IN MEDICINE AND BIOLOGY, vol. 60, no. 2, pp. 453–471, 2014.
@article{5797078,
  abstract     = {In transcranial magnetic stimulation (TMS), an applied alternating magnetic field induces an electric field in the brain that can interact with the neural system. It is generally assumed that this induced electric field is the crucial effect exciting a certain region of the brain. More specifically, it is the component of this field parallel to the neuron's local orientation, the so-called effective electric field, that can initiate neuronal stimulation. Deeper insights on the stimulation mechanisms can be acquired through extensive TMS modelling. Most models study simple representations of neurons with assumed geometries, whereas we embed realistic neural trajectories computed using tractography based on diffusion tensor images. This way of modelling ensures a more accurate spatial distribution of the effective electric field that is in addition patient and case specific. The case study of this paper focuses on the single pulse stimulation of the left primary motor cortex with a standard figure-of-eight coil. Including realistic neural geometry in the model demonstrates the strong and localized variations of the effective electric field between the tracts themselves and along them due to the interplay of factors such as the tract's position and orientation in relation to the TMS coil, the neural trajectory and its course along the white and grey matter interface. Furthermore, the influence of changes in the coil orientation is studied. Investigating the impact of tissue anisotropy confirms that its contribution is not negligible. Moreover, assuming isotropic tissues lead to errors of the same size as rotating or tilting the coil with 10 degrees. In contrast, the model proves to be less sensitive towards the not well-known tissue conductivity values.},
  author       = {De Geeter, Nele and Crevecoeur, Guillaume and Leemans, Alexander and Dupré, Luc},
  issn         = {0031-9155},
  journal      = {PHYSICS IN MEDICINE AND BIOLOGY},
  keywords     = {LIMITATIONS,diffusion tensor imaging (DTI),transcranial magnetic stimulation (TMS),primary motor cortex (M1),INDEPENDENT IMPEDANCE METHOD,HUMAN MOTOR CORTEX,BIOLOGICAL TISSUES,FIBER,TRACTOGRAPHY,DIFFUSION TENSOR MRI,HUMAN BRAIN,tractography,effective electric field,DEPRESSION,TRANSCRANIAL MAGNETIC STIMULATION},
  language     = {eng},
  number       = {2},
  pages        = {453--471},
  title        = {Effective electric fields along realistic DTI-based neural trajectories for modelling the stimulation mechanisms of TMS},
  url          = {http://dx.doi.org/10.1088/0031-9155/60/2/453},
  volume       = {60},
  year         = {2014},
}

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