Evaluation of three-dimensional anisotropic head model for mapping realistic electromagnetic fields of brain tissues

Abstract

Electromagnetic fields provide fundamental data for the imaging of electrical tissue properties, such as conductivity and permittivity, in recent magnetic resonance (MR)-based tissue property mapping. The induced voltage, current density, and magnetic flux density caused by externally injected current are critical factors for determining the image quality of electrical tissue conductivity. As a useful tool to identify bio-electromagnetic phenomena, precise approaches are required to understand the exact responses inside the human body subject to an injected currents. In this study, we provide the numerical simulation results of electromagnetic field mapping of brain tissues using a MR-based conductivity imaging method. First, we implemented a realistic three-dimensional human anisotropic head model using high-resolution anatomical and diffusion tensor MR images. The voltage, current density, and magnetic flux density of brain tissues were imaged by injecting 1 mA of current through pairs of electrodes on the surface of our head model. The current density map of anisotropic brain tissues was calculated from the measured magnetic flux density based on the linear relationship between the water diffusion tensor and the electrical conductivity tensor. Comparing the current density to the previous isotropic model, the anisotropic model clearly showed the differences between the brain tissues. This originates from the enhanced signals by the inherent conductivity contrast as well as the actual tissue condition resulting from the injected currents.

In vivo mapping of current density distribution in brain tissues during deep brain stimulation (DBS)

“…[12][13][14] In addition, the conductivity distribution of living tissues can be obtained from two independent current injection data inside the imaging objects. 7,9,12 From numerical simulation and mimicked phantom experiments, 12,15,16 several studies have proposed that this method has a potential for visualizing current density distribution in living tissues. However, there was a few validation studies on living tissues.…”

“…21,22 Together with electrode size and shape, boundary geometry, current flow is also affected by tissue conditions such as anisotropy. 15,17 The difference around electrode regions between the measured B z and calculated B z 0 originates from the degree of brain tissue anisotropy. Figure 3 shows the resulting current density images of the in vivo brain in two different imaging slices.…”