Investigation of electrical conductivity changes during brain functional activity in 3T MRI

Abstract

Blood oxygenation level-dependent functional magnetic resonance imaging (fMRI) is widely used to visualize brain activation regions by detecting hemodynamic responses associated with increased metabolic demand. Although alternative MRI methods have been employed to monitor functional activities, the investigation of in-vivo electrical property changes during brain function remains limited. In this study, the relationship between fMRI signals and electrical conductivity (measured at the Larmor frequency) changes was explored using phase-based electrical property tomography. Results revealed consistent patterns: conductivity changes showed negative correlations, with conductivity decreasing in functionally active regions whereas $B_1$ phase mapping exhibited positive correlations around the activation regions. These observations were consistent across the motor and visual cortex activations To further substantiate these findings, electromagnetic radio-frequency simulations that modeled activation states with varying conductivities were conducted, demonstrating trends similar to in-vivo results for $B_1$ phase and conductivity. Notably, we observed that false-positive activation signals could occur depending on the level of noise and the reconstruction method applied. These findings suggested that in-vivo electrical conductivity changes can indeed be measured during brain activity. However, further investigation is needed to fully understand the underlying mechanisms driving these measurements.