Fluid-modulated RF ablation:: In-vitro experiments

Purpose: To evaluate the potential of different fluids to enhance the effect of radiofrequency ablation. Materials and Methods: A bipolar radiofrequency system with an internally cooled needle electrode was used to heat three samples of 16 different fluids. Each sample had a volume of 20 ml. The generator output was set to 20 watt as recommended by the vendor. Energy was applied until the temperature of the sample reached 80 degrees C or the duration of heating exceeded 30 minutes. If a fluid was not able to be heated because the resistance was too high, 15 ml of the fluid were mixed with 5 ml of a 1-mol saline solution. During energy deposition, the temperature was measured every 15 seconds. The applied energy, impedance, resistance, voltage and flowing current were recorded continuously. Results: The ionic contrast agent Telebrix (R) Gastro was heated to 80 degrees C within 620 +/- 95 seconds which was the shortest time needed. It was not possible to heat the contrast agents Solutrast 300 (R), Isovist 240 (R), Gadovist (R) and Lipiodol (R) as well as a 40% glucose solution and 95% ethanol. The longest time was needed to heat the 40% glucose solution + the 1-mol saline solution (1755 +/- 26 seconds). The correlation coefficients (Pearson) showed only a marginal connection between resistance and maximum temperature (r=0.52) and duration for heating up to 80 degrees C, respectively (r= -0.54). The same is true for the connection between impedance and maximum temperature (r=0.52) as well as duration for heating up to 80 C (r= -0.57). Conclusion: The selection of an appropriate fluid allows an increase in the effect of radiofrequency ablation or the generation of a protective effect. Especially HAES, Magnevist (R) and Telebrix (R) Gastro are suitable for enhancing heating. Glucose solution or non-ionic contrast agents could be used to generate a protective effect during radiofrequency ablation. The heating of fluids by means of a bipolar radiofrequency ablation system is not only influenced by the electric properties but also by other parameters such as the specific heat capacity.