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Background. The impact of vascular cooling effects in hepatic microwave ablation (MWA) is controversially discussed. The objective of this study was a systematic assessment of vascular cooling effects in hepatic MWA ex vivo. Methods. Microwave ablations were performed in fresh porcine liver ex vivo with a temperature-controlled MWA generator (902-928 MHz) and a non-cooled 14-G-antenna. Energy input was set to 9.0 kJ. Hepatic vessels were simulated by glass tubes. Three different vessel diameters (3.0, 5.0, 8.0 mm) and vessel to antenna distances (5, 10, 20 mm) were examined. Vessels were perfused with saline solution at nine different flow rates (0-500 mL/min). Vascular cooling effects were assessed at the largest cross-sectional ablation area. A quantitative and semi-quantitative/morphologic analysis was carried out. Results. 228 ablations were performed. Vascular cooling effects were observed at close (5 mm) and medium (10 mm) antenna to vessel distances ( P < .05). Vascular cooling effects occurred around vessels with flow rates ≥1.0 mL/min ( P < .05) and a vessel diameter ≥3 mm ( P < .05). Higher flow rates did not result in more distinct cooling effects ( P > .05). No cooling effects were measured at large (20 mm) antenna to vessel distances ( P > .05). Conclusion. Vascular cooling effects occur in hepatic MWA and should be considered in treatment planning. The vascular cooling effect was mainly affected by antenna to vessel distance. Vessel diameter and vascular flow rate played a minor role in vascular cooling effects.

Purpose: Radiofrequency ablation (RFA) for primary liver tumors and liver metastases is restricted by a limited ablation size. Multipolar RFA is a technical advancement of RFA, which is able to achieve larger ablations. The aim of this ex vivo study was to determine optimal ablation parameters for multipolar RFA depending on applicator distance and energy input., Methods: RFA was carried out ex vivo in porcine livers with three internally cooled, bipolar applicators in multipolar ablation mode. Three different applicator distances were used and five different energy inputs were examined. Ablation zones were sliced along the cross-sectional area at the largest ablation diameter, orthogonally to the applicators. These slices were digitally measured and analyzed., Results: Sixty RFA were carried out. A limited growth of ablation area was seen in all test series. This increase was dependent on ablation time, but not on applicator distance. A steady state between energy input and energy loss was not observed. A saturation of the minimum radius of the ablation zone was reached. Differences in ablation radius between the three test series were seen for lowest and highest energy input ( P < .05). No differences were seen for medium amounts of energy ( P > .05)., Conclusions: The ablation parameters applicator distance and energy input can be chosen in such a way, that minor deviations of the preplanned ablation parameters have no influence on the size of the ablation area.