Study of flow effects on temperature‐controlled radiofrequency ablation using phantom experiments and forward simulations

Medical Physics, vol. 48, pp. 4754–4768

Abstract

Abstract Purpose Blood flow is known to add variability to hepatic radiofrequency ablation (RFA) treatment outcomes. However, few studies exist on its impact on temperature‐controlled RFA. Hence, we investigate large‐scale blood flow effects on temperature‐controlled RFA in flow channel experiments and numerical simulations. Methods Ablation zones were induced in tissue‐mimicking, thermochromic phantoms with a single flow channel, using an RF generator with temperature‐controlled power delivery and a monopolar needle electrode. Channels were generated by molding the phantom around a removable rod. Channel radius and saline flow rate were varied to study the impact of flow on (i) the ablated cross‐sectional area, (ii) the delivered generator power, and (iii) the occurrence of directional effects on the thermal lesion. Finite volume simulations reproducing the experimental geometry, flow conditions, and generator power input were conducted and compared to the experimental ablation outcomes. Results Vessels of different channel radii affected the ablation outcome in different ways. For mm, the ablated area decreased with increasing flow rate while the energy input was hardly affected. For mm and mm, the energy input increased toward larger flow rates; for these radii, the ablated area decreased and increased toward larger flow rates, respectively, while still being reduced overall as compared to the reference experiment without flow. Directional effects, that is, local shrinking of the lesion upstream of the needle and an extension thereof downstream, were observed only for the smallest radius. The simulations qualitatively confirmed these observations. As compared to performing the simulations without flow, including flow effects in the simulations reduced the mean absolute error between experimental and simulated ablated areas from 0.23 to 0.12. Conclusion While the temperature control mechanism did not detect the heat sink effect in the case of the smallest channel radius, it counteracted the heat sink effect in the case of the larger channel radii with an increased energy input; this explains the increase in ablated area toward high flow rates (for mm). The experiments in a simple phantom setup, thus, contribute to a good understanding of the phenomenon and are suitable for model validation.

Authors 8

1. Teresa Nolte Aachen Department of Physics of Molecular Imaging Systems Institute for Experimental Molecular Imaging Department of Physics of Molecular Imaging Systems Institute for Experimental Molecular Imaging

   RWTH Aachen University

   Affiliation as printed

   Department of Physics of Molecular Imaging systems Institute for Experimental Molecular Imaging RWTH Aachen University Aachen Germany

   Department of Physics of Molecular Imaging systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany

2. Nikhil Vaidya corresponding Aachen Faculty of Civil Engineering

   RWTH Aachen University

   Affiliation as printed

   Faculty of Civil Engineering RWTH Aachen University Aachen Germany

   Faculty of Civil Engineering, RWTH Aachen University, Aachen, Germany

3. Marco Baragona
   Affiliation as printed

   Philips Research Europe Eindhoven The Netherlands

   Philips Research Europe, Eindhoven, The Netherlands

4. Aaldert Elevelt
   Affiliation as printed

   Philips Research Europe Eindhoven The Netherlands

   Philips Research Europe, Eindhoven, The Netherlands

5. Valentina Lavezzo
   Affiliation as printed

   Philips Research Europe Eindhoven The Netherlands

   Philips Research Europe, Eindhoven, The Netherlands

6. Ralph Maessen
   Affiliation as printed

   Philips Research Europe Eindhoven The Netherlands

   Philips Research Europe, Eindhoven, The Netherlands

7. Volkmar Schulz Aachen Department of Physics of Molecular Imaging Systems Institute for Experimental Molecular Imaging Physics Institute III B Department of Physics of Molecular Imaging Systems Institute for Experimental Molecular Imaging

   Fraunhofer Institute for Digital Medicine · RWTH Aachen University

   Affiliation as printed

   Department of Physics of Molecular Imaging systems Institute for Experimental Molecular Imaging RWTH Aachen University Aachen Germany

   Fraunhofer Institute for Digital Medicine MEVIS Bremen Germany

   Hyperion Hybrid Imaging Systems GmbH Aachen Germany

   Physics Institute III B RWTH Aachen University Aachen Germany

   Department of Physics of Molecular Imaging systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany

   Fraunhofer Institute for Digital Medicine MEVIS, Bremen, Germany

   Hyperion Hybrid Imaging Systems GmbH, Aachen, Germany

   Physics Institute III B, RWTH Aachen University, Aachen, Germany

8. Karen Veroy

   Eindhoven University of Technology

   Affiliation as printed

   Center for Analysis Scientific Computing, and Applications Eindhoven University of Technology Eindhoven The Netherlands

   Center for Analysis, Scientific Computing, and Applications, Eindhoven University of Technology, Eindhoven, The Netherlands