ARTICLE IN PRESS JID: JJBE [m5G;February 26, 2019;15:4] Medical Engineering and Physics xxx (xxxx) xxx Contents lists available at ScienceDirect Medical Engineering and Physics journal homepage: www.elsevier.com/locate/medengphy Ex vivo validation of microwave thermal ablation simulation using different flow coefficients in the porcine liver Frank Hübner a,∗ , Roland Schreiner a , Carolin Reimann b , Babak Bazrafshan a , Benjamin Kaltenbach a , Martin Schüßler b , Rolf Jakoby b , Thomas Josef Vogl a a Institute for Diagnostic and Interventional Radiology, Johann Wolfgang Goethe – University Hospital, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany b Institute for Microwave Engineering and Photonics, Technische Universität Darmstadt, Merckstrasse 25, 64283 Darmstadt, Germany a r t i c l e i n f o Article history: Received 5 April 2018 Revised 6 February 2019 Accepted 11 February 2019 Available online xxx Keywords: Microwave thermal ablation Simulation Liver tissue Flow coefficient Heat distribution a b s t r a c t The purpose of the study was to validate the simulation model for a microwave thermal ablation in ex vivo liver tissue. The study aims to show that heat transfer due to the flow of tissue water during ablation in ex vivo tissue is not negligible. Ablation experiments were performed in ex vivo porcine liver with microwave powers of 60 W to 100 W. During the procedure, the temperature was recorded in the liver sample at different distances to the applicator using a fiber-optic thermometer. The position of the probes was identified by CT imaging and transferred to the simulation. The simulation of the heat distribution in the liver tissue was carried out with the software CST Studio Suite. The results of the simulation with different flow coefficients were compared with the results of the ablation experiments using the Bland– Altman analysis. The analysis showed that the flow coefficient of 90,000 W/(K ∗ m 3 ) can be considered as the most suitable value for clinically used powers. The presented simulation model can be used to calculate the temperature distribution for microwave ablation in ex vivo liver tissue. © 2019 Published by Elsevier Ltd on behalf of IPEM. 1. Introduction Thermal ablation techniques such as radiofrequency ablation (RFA), microwave ablation (MWA) and laser-induced interstitial thermotherapy (LITT) can be used in interventional oncology for the treatment of liver malignancies. The application of hyperther- mic energy to destroy tumor cells is based on the denaturation of proteins and the subsequent loss of function leading to cell death. Proteins begin to denature already at about 40 °C, but irreversible coagulation necrosis occurs only from about 60 to 100 °C [1,2]. Microwave coagulation was developed in the early 1980s during hepatic resection in order to achieve hemostasis [3] and has sub- stantially changed the field of thermal ablation in interventional oncology [2]. In oncology, microwave tumor ablation is a minimally invasive treatment for early-stage HCC and oligonodular metastases (three or fewer lesions) and especially for non-resectable liver lesions. During the treatment, the applicator is positioned percuta- neously in the tumor under ultrasound or CT imaging. The emitted electromagnetic energy at the tip of the applicator excites water ∗ Corresponding author. E-mail address: frank.huebner@kgu.de (F. Hübner). molecules in the tissue, which results in heat and coagulates the tissue. As the success of the ablation highly depends on the po- sitioning of the applicator tip and the conspicuity of the target tumor, intensive research is currently being conducted on MR- compatible MWA systems. MR-guidance offers appealing charac- teristics such as excellent soft-tissue resolution, sometimes even without additional use of contrast agent, and the potential of real- time thermosensitive imaging [4]. For the development of these new microwave applicators, ex- perimental tests are carried out in ex vivo tissues in order to eval- uate their mode of action and efficiency [4]. Furthermore, theoret- ical models of the thermal therapy are used for the evaluation. For those models, the Maxwell’s equation set as well as the Pennes Bioheat equation is usually applied. The latter includes a term for the heat loss through the microvascular blood perfusion [5]. The heat loss through blood perfusion is often neglected in ex vivo samples because there is no perfusion [6]. However, heating in the microwave ablation leads to partial boiling and evaporation of tissue water. The extracellular and intra- cellular water flows through destroyed tissue cells and via vessels away from the ablation zone resulting in heat transfer. The flow of water can be clearly observed in MR imaging at high temporal resolution. Therefore, the heat transfer in an ex vivo liver is not negligible. https://doi.org/10.1016/j.medengphy.2019.02.007 1350-4533/© 2019 Published by Elsevier Ltd on behalf of IPEM. Please cite this article as: F. Hübner, R. Schreiner and C. Reimann et al., Ex vivo validation of microwave thermal ablation simulation using different flow coefficients in the porcine liver, Medical Engineering and Physics, https://doi.org/10.1016/j.medengphy.2019.02.007