Imaging Intra- and Extracellular Conductivity using MR based Conductivity Tensor Imaging

Abstract

Imaging electrical conductivity may reveal relationships between biological tissues, cellular structures, and physiological processes. Biological tissues are primarily composed of major ions such as Na+ and K+, with varying concentrations and mobility within the cellular structures. These tissues consist of intracellular and extracellular fluids separated by cell membranes, and their electrical conductivity can be expressed as a function of ion concentration and mobility. This study introduces Conductivity Tensor Imaging (CTI) to independently reconstruct the electrical conductivity of intra- and extracellular compartments in biological tissues using MRI. We validated this method using a conductivity phantom with three compartments filled with electrolytes and/or giant vesicle suspensions. These vesicles mimic cell-like materials with thin insulating membranes, providing a realistic model for cellular structures. Measurements showed that high-frequency conductivity closely matched low-frequency conductivity in normal electrolytes. However, in the giant vesicle compartment, the conductivity of extracellular (EC) and intracellular (IC) regions correlated with cell volume fraction. In vivo human brain imaging using CTI revealed significant EC and IC conductivity variations across different brain regions, corresponding to underlying cellular compositions and structures. CTI introduces a novel MR contrast mechanism to distinctly measure IC and EC conductivities. Our findings highlight the potential of CTI to enhance our understanding of brain microstructure and its physiological processes through detailed conductivity mapping. This method signifies a notable advancement in non-invasive imaging, providing novel insights into the electrical properties of biological tissues and their implications for biophysical properties.