Electrical conductivity imaging of postmortem canine brains using magnetic resonance electrical impedance tomography

Cross-sectional images of a conductivity distribution inside a postmortem canine brain were reconstructed using Magnetic Resonance Electrical Impedance Tomography (MREIT) techniques. Injecting currents through pairs of surface electrodes, we measured distributions of induced magnetic flux densities inside the brain using a 3T MRI scanner. We used a conductivity image reconstruction algorithm called the harmonic Bz algorithm to produce conductivity images. The spatial resolution of conductivity images was 1.406 x 1.406 mm2 and they showed a clear contrast between white and gray matters. Conductivity ratios of white to gray matters were between 1.13 and 1.20 depending on the choice of a region of interest in reconstructed images. Higher conductivity values of white matters stem from the fact that reconstructed equivalent isotropic conductivity values of white matters are more affected by longitudinal components of their anisotropic conductivity tensors. In this postmortem experimental study, the amplitude of the injection current was 40 mA that is too high any in vivo experiments. From the postmortem experimental results summarized in this paper, we proposed an experimental protocol for in vivo animal experiments in our future studies.