Analysis of the interaction between an MRI coil and a heterogeneous sample

A theoretical analysis of the interaction between a magnetic resonance imaging radio frequency coil and a heterogeneous sample consisting of two conducting regions separated by a non-conducting membrane is presented. The effect of the capacitive coupling between the two regions is treated. Expressions are obtained for the power dissipation in the sample and the electrical impedance of the coil and an equivalent electrical circuit which models the interaction is presented. The sample power dissipation in this case lacks the usual quadratic dependence on frequency observed with homogeneous samples. Results of the analysis are shown to agree well with observation in an experimental coil-sample system.