TDCS Simulation Research In Consideration Of The Anisotropy Of The White Matter

Transcranial direct current stimulation(tDCS) is a noninvasive stimulation technique, which current or voltage is delivered at human's brain, leading to the electrical field pass through the whole head that could be a treatment for neurological and psychiatric disorders. In consideration of safety and reliability, scientists and clinicians used to apply the finite element methods to simulate the tDCS process, which could provide more accurate results in consideration of the complex geometry and boundary conditions. The influence of anisotropy in the White Matter(WM) is not well understood, so the goal of this thesis is to investigate insight into the effect of anisotropy of WM conductivity on the electric field distribution.To ensure the simulation more effective and easier, the head model was built based on the standard three layer sphere model, which was positioned in MNI space to facilitate the interpretation of spatial coordinates. In previous studies, the WM conductivity was assigned constant value. To get a more accurate simulation, this thesis presented a method which could reflect the character of the anisotropic conductivity of WM by dividing the third layer of the spherical model based on the volume constraint model. The contour plot results showed that the electric field distribution in one anisotropic model was similar to some parameters used by some foreign researchers. Then the electric field and current density at the key point were calculated, the results were in accordance with the former researches on the isotropic model, and the calculations of the anisotropic model would provide a reference for practical application.To further investigate the WM anisotropic conductivity, the third layer was divided into three parts representing cerebrospinal fluid, gray matter and WM, and a cylindrical neural fiber tract was built to reflect the anisotropy of the WM. Finally, the electric field contour plots and path graphs which could clearly reflect the variation of the electric field were given. Some variations which can't be easily found in contour plots would be found on the path graphs. In the central region of neural fiber area, the electric field presented peak at the second path and trough at the third path in the anisotropic models, while it presented gradual step-down trend in the isotropic model. The results have fully reflected the characteristic of the anisotropy of the WM, achieving the aim of this study.