Influence of anisotropic conductivity on EEG source reconstruction: investigations in a rabbit model

Abstract

The aim of our work was to quantify the influence of white matter anisotropic conductivity information on electroencephalography (EEG) source reconstruction. We performed this quantification in a rabbit head using both simulations and source localization based on invasive measurements. In vivo anisotropic (tensorial) conductivity information was obtained from magnetic resonance diffusion tensor imaging and included into a high-resolution finite-element model. When neglecting anisotropy in the simulations, we found a shift in source location of up to 1.3 mm with a mean value of 0.3 mm. The averaged orientational deviation was 10 degree and the mean magnitude error of the dipole was 29%. Source localization of the first cortical components after median and tibial nerve stimulation resulted in anatomically verified dipole positions with no significant anisotropy effect. Our results indicate that the expected average source localization error due to anisotropic white matter conductivity is within the principal accuracy limits of current inverse procedures. However, larger localization errors might occur in certain cases. In contrast, dipole orientation and dipole strength are influenced significantly by the anisotropy. We conclude that the inclusion of tissue anisotropy information improves source estimation procedures.

Influence of white matter inhomogeneous anisotropy on EEG forward computing

“…To apply FEM, we assign anisotropic conductivity tensor to each element of the WM layer. We assume that the conductivity tensors share the same eigen vectors with the effective diffusion tensors measured by DT-MRI 6,7,12,13,21 . Then, we consider the conductivity tensor for a WM finite element as 6,7,12,13 ( 1) where S is orthogonal matrix of unit length eigenvectors of the measured diffusion tensor at the barycentre of the WM finite element, σ long is the parallel (longitudinal) eigen values and σ trans is the perpendicular (transverse) eigen values where…”

“…the movement of both water molecules and electrically charged particles (ions) 12 . To implement conductivity tensor we assume that the same structural features that result in anisotropic mobility of water molecules also result in anisotropic conductivity.…”

“…To overcome volume obstacle, Wolters 6 proposed Volume constraint, which restricts the geometric mean and the volume of the conductivity tensor as constants. The Volume constraint is defined as 6,7,12 (4) where σ iso is isotropic conductivity.…”

“…They found that WM anisotropy and inhomogeneity would affect the scalp EEG. Gullmar et al 12,13 also generated anisotropic conductivities for Volume constrained WM and simulated on rabbit head model. They mentioned that the anisotropy of WM conductivity affect the EEG forward and inverse computations.…”

Biomedical Visualization

“…The visualization of return currents in bioelectric field problems can reveal important details about the distribution of sources, interactions at conductivity boundaries, and the effect of geometric distortion on bioelectric fields. By integrating the stream surfaces with a visualization of the diffusion tensors representing the white matter, we can better understand the relationship between structural, spatial relationships [116,117].…”