Low‐frequency conductivity tensor of rat brain tissues inferred from diffusion MRI

Abstract

Conductivity tensor maps of the rat brain were obtained using diffusion magnetic resonance imaging (MRI). Signal attenuations in the cortex and the corpus callosum were measured using the stimulated echo acquisition mode (STEAM) sequence with b factors up to 6000 s/mm(2). Our previously published method was improved to infer 3 x 3 conductivity tensor at the low-frequency limit. The conductivity tensor of the tissue was inferred from the fast component of the diffusion tensor and a fraction of the fast component. The mean conductivity (MC) of the cortex and the corpus callosum was 0.52 and 0.62 S/m, respectively. Diffusion-weighted images were obtained with b factors up to 4500 s/mm(2). Conductivity tensor images were calculated from the fast diffusion tensor images. Tissues with highly anisotropic cellular structures, such as the corpus callosum, the internal capsule, and the trigeminal nerve, exhibited high anisotropy in conductivity. The resulting values corresponded to conductivities at the low-frequency limit because our method assumed electric currents flowing only through extracellular fluid.

Ionic charge transport between blockages: Sodium cation conduction in freshly excised bulk brain tissue

“…8 Similarly, the local anisotropic diffusion constants inferred from proton diffusion-MRI measurements in rat brain are also ∼ 10 −9 m 2 /sec. 10 Thus, the diffusion constant of sodium in freshly excised bulk human brain tissue estimated from measurements of its electrical conductivity is comparable to local values determined non-invasively with MRI and diffusion-MRI.…”

“…For example, ions diffusing through intercellular fluid must navigate through a dense distribution of cells with diameters up to 40 µm. 10,11 All told, sodium cations would appear to tortuously diffuse among many cells in the brain's complex inhomogeneous medium before being effectively blocked.…”

3D Stationary electric current density in a spherical tumor treated with low direct current: An analytical solution

“…They dictate the bulk current densities, not the microscopic-scale (or cellular/subcelluar-level) pathways that result from an applied stimulus, and are thus very important in the analysis of a wide range of biomedical applications [Miklavčič et al, 2006b]. That is why we evaluated, through use of the mean conductivity (average conductivity between three principal axes), the tissue electric conductivity without consideration of anisotropy [Sekino et al, 2009]. In this paper, the mean conductivity is simply represented by s. We make the following assumptions, taking these facts into account:…”

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

“…The current density depends on the actual pathways of current flow inside the brain, and shows their values when current flows are parallel to fiber direction. [23][24][25][26] CSF showed highest values due to its inherent high conductivity of 2.0 S/m. The current density of gray matter was lowest, because it consists of numerous cell bodies and relatively few myelinated axons.…”