In vivo determination of electric conductivity and permittivity using a standard MR system

Abstract

The electric properties of human tissue, i.e., the electric conductivity and permittivity, can be used as an additional diagnostic parameter or might be helpful for the prediction of the local SAR during MR measurements. In this study, a new approach “Electric Properties Tomography” (MR-EPT) is presented, which derives the patient’s electric properties using a standard MR system. To this goal, the spatial transmit and receive sensitivity distributions of the applied RF coil are measured. According to the first Maxwell equation, dividing the spatial derivatives of these sensitivities by the corresponding electric field leads to the desired spatial distribution of conductivity and permittivity. The electric field can be estimated using the geometry of the involved RF coil and the patient’s geometry, known from the acquired MR images. Thus, MR-EPT does not apply externally mounted electrodes, currents, or RF probes. The spatial resolution of the reconstructed conductivity and permittivity is of the order of the spatial resolution of the measured MR images. In this study, phantom experiments underline the principle feasibility of MR-EPT.