MR imaging of RF heating using a paramagnetic doped agarose phantom

In this paper, we present the first description of a technique to visualize and quantitate radiofrequency (RF) heating of a tissue phantom during a magnetic resonance imaging (MRI) procedure. We evaluated the heating patterns of four 10 cm diameter transmit/receive surface coils with differing degrees of distributed capacitance. The tissue phantom was a 6% agarose gel doped with 40 mM Na(4)HTm[DOTP], and possesses a conductivity intermediate to human muscle and fat. Heating was discerned via phase difference mapping using the large temperature dependent chemical shift coefficient for 23Na in Na(4)HTm[DOTP]. This coefficient is -0.5 ppm/ degrees C. Heating was highest where the phantom was closest to the surface coils, dropping off towards the center of the coil. No significant difference was observed in the heating patterns between the different surface coils. For the experimental setups used in this study, electric field 'hot spots' at the areas corresponding to the placement of the capacitor gaps were not observed.