Imaging of Electric Permittivity and Conductivity Using Magnetic Resonance Imaging

The purpose of this study is to propose a method for noninvasively measuring the spatial distribution of electric permittivity and conductivity using magnetic resonance imaging (MRI). In this method, weak radio-frequency (RF) electric current is applied to the sample through surface electrodes. The permittivity and conductivity of the sample are estimated from a set of images obtained with and without application of the current. The algorithm for calculating these quantities was evaluated using numerical simulations and experiments. We assumed a cylindrical sample having relative permittivity of 40 and conductivity of 0.14 S/m. The simulation showed that suppression of nonuniformity of a RF magnetic field is important for reducing errors in measurement. Experiments were carried out using a 4.7 T MRI system and a sample consisting of a saline solution and ethanol. The estimated permittivity and conductivity at the center of the sample were approximately 40 and 2 S/m, respectively. The method has the advantage of noninvasive and high-resolution imaging of the electric properties of the sample, and is easily applicable to biological tissues and human subjects.