Correlation of quantitative conductivity mapping and total tissue sodium concentration at 3T/4T
16 July 2019
The conductivity of tissue is a fundamental property that characterizes its capability to conduct electrical current when external electromagnetic fields are applied and is also associated with tissue health. Consequently, mapping the conductivity of brain tissue can potentially serve as a biomarker and may provide information relating to a range of brain diseases.
In this study, the correlation between conductivity and Na+ content was evaluated by performing conductivity measurements on samples with different sodium (Na+) and agarose concentrations using a dielectric probe. Brain conductivity and total Na+ content maps were then measured in 8 healthy subjects using phase-based MREPT and sodium MRI. Following co-registration and spatial normalization to the 1 mm 152 MNI brain atlas, the relationship between conductivity and tissue sodium concentration (TSC) was examined within different brain regions.
It was found that the conductivities of agarose gels increased linearly with NaCl concentration, while remaining almost independent of agarose content. When measured in healthy subjects, conductivities showed a positive correlation with total tissue sodium concentration (R = 0.39, P < 0.005). The same trend was found in gray matter (R = 0.36, P < 0.005) and in white matter (R = 0.28, P < 0.05).
Based on these findings, it can be demonstrated that tissue conductivity shows a positive correlation with total sodium concentration and that conductivity might serve as a novel technique with which to visualize the total tissue electrolyte concentration. However, refinements in the consideration of e.g., tissue water content, would be necessary to improve the quantitative value.