Study of flow effects on temperature-controlled radio-frequency ablation using phantom experiments and forward simulations

Abstract

PurposeBlood perfusion is known to add variability to hepatic radiofrequency ablation (RFA) treatment outcomes. Simulation-assisted treatment planning taking into account blood perfusion may solve this problem in the future. Hence, this study aims to study perfusion effects on RFA in a controlled environment and to compare the outcome to a prediction made using finite volume simulations. MethodsAblation zones were induced in tissue-mimicking, thermochromic ablation phantoms with a single flow channel, using a RF generator with needle temperature controlled power delivery and a monopolar needle electrode. Channel radius and saline flow rate were varied and the impact of saline flow on the ablated cross-sectional area, on a potential occurrence of directional effects as well as on the delivered generator power input was studied. Finite-volume simulations reproducing the experimental geometry, flow conditions and generator power input were conducted in a second step and compared to the experimental ablation outcomes. ResultsVessels of different radii affected the ablation result in different manners. For the channel radius of 0.275 mm both the ablated area and energy input reduced with increasing flow rate. For radius 0.9 mm the ablated area reduced with increasing flow rate but the energy input increased. An increasing area and energy input were observed towards larger flow rates for the channel radius of 2.3 mm. Directional effects, i.e., shrinking of the lesion upstream of the needle and an extension thereof downstream, were observed only for the smallest channel radius. The simulations qualitatively confirmed these observations. When using the simulations to make a prediction of ablation outcomes with flow, the mean absolute error between experimental and predicted ablation outcomes was reduced from 23% to 12% as compared to neglecting flow effects. ConclusionSimulations can improve the prediction of RFA ablation regions in the presence of various blood flow effects. Our findings therefore underline the potential of simulation-assisted, patient-individual RFA treatment planning and guidance for the prediction of RFA outcomes in the presence of blood flow. Additional comments-Teresa Nolte and Nikhil Vaidya contributed equally to this work. -Volkmar Schulz and Karen Veroy contributed equally to this work. -A single reference experiment, i.e., not using a flow channel, and the image in the upper left corner of Figure 4 were included into a publication submitted to Int. J. Hyperthermia for model validation purposes. O_FIG O_LINKSMALLFIG WIDTH=178 HEIGHT=200 SRC="FIGDIR/small/172957v1_fig4.gif" ALT="Figure 4"> View larger version (122K): org.highwire.dtl.DTLVardef@935182org.highwire.dtl.DTLVardef@1cc4eedorg.highwire.dtl.DTLVardef@51ad9aorg.highwire.dtl.DTLVardef@5c9625_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFig. 4C_FLOATNO Experimentally obtained ablation zones for all RFA experiments and the corresponding reference experiments. The experimental and simulated 70{degrees}C temperature contours are marked by a blue and a black line, respectively. The ablation needle was inserted from the left side. Saline flow was established from right to left through the flow channel located below the ablation area. Radius and flow rate for each experiment were as specified within the figure below the ablation zones. In four experiments, the experimental ablation zone shows an unexpected bump structure, which we marked by white arrows. The numbering of the experiments refers to Table 1. C_FIG