Impedance MRI and MR neuroimaging

Mapping of electromagnetic fields and electric properties of the brain is helpful in understanding the fundamentals of brain function. This paper introduces recent progress in magnetic resonance imaging (MRI) techniques to obtain the electric properties of the biological tissues and weak magnetic fields arising from neuronal electrical activities. There are two approaches for impedance MRI: Application of external electric currents to the sample and observation of the resulting changes in images provide a straightforward way to estimate the electric properties of the sample. Inferring the tissue conductivity from the water diffusion coefficient provides a less invasive method to estimate the tissue conductivity. Considering that MRI is inherently sensitive to magnetic fields generated in the samples, detection of magnetic fields arising from neuronal electrical activities using MRI is an attractive approach for dramatically improving the temporal resolution of functional MRI. Evaluating the sensitivity of MRI to weak magnetic fields is crucial in realizing this detection. Some papers report that the neuronal magnetic fields are detectable using MRI.