An Efficient Method for Electrical Conductivity Measurement in the RF Range

Many of the hardware procedure like radiofrequency (RE) coils testing and simulation experiments such as the estimation of temperature changes in magnetic resonance imaging experiments require saline phantoms. These kinds of experimental models are generally obtained using a well-defined container filled with conductive salt solution (i.e., diluted NaCl solution) or using a combination of conductive gel with a semi-solid consistency. These phantoms are commonly prepared according to the standards values of the principal parameter concerning theirs dielectric properties (i.e., permittivity and electrical conductivity). Although several permittivity measurement methods have already been reported in literature, most of the data describing the electrical conductivity of these saline solutions provided by different authors are often conflicting and the frequencies of each measure are not always specified. Besides, low-cost commercial conductimeters could provide measurements overlooking the conductivity dependence on the frequency, while the measurements in the RF range require costly coaxial probes which work with network analyzers with multi-electrodes working in solution. In this article, we describe a system based on self-made coil designed to measure the electrical conductivity of conductive solutions in the RE range, without any contact between the sample and the measurement probe. The estimated value of conductivity has been performed combining theoretical calculation of induced resistance in the phantom volume and experimental measurements using workbench instrumentations. The method can be applied to the whole RE range measurements by tuning the capacitor value of the resonant circuit. (C) 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 37B: 160-166, 2010