Experimental Evaluation of the Heat Sink Effect in Hepatic Microwave Ablation

Abstract

PurposeTo demonstrate and quantify the heat sink effect in hepatic microwave ablation (MWA) in a standardized ex vivo model, and to analyze the influence of vessel distance and blood flow on lesion volume and shape.Materials and Methods108 ex vivo MWA procedures were performed in freshly harvested pig livers. Antennas were inserted parallel to non-perfused and perfused (700,1400 ml/min) glass tubes (diameter 5mm) at different distances (10, 15, 20mm). Ablation zones (radius, area) were analyzed and compared (Kruskal-Wallis Test, Dunn’s multiple comparison Test). Temperature changes adjacent to the tubes were measured throughout the ablation cycle.ResultsMaximum temperature decreased significantly with increasing flow and distance (p<0.05). Compared to non-perfused tubes, ablation zones were significantly deformed by perfused tubes within 15mm distance to the antenna (p<0.05). At a flow rate of 700ml/min ablation zone radius was reduced to 37.2% and 80.1% at 10 and 15mm tube distance, respectively; ablation zone area was reduced to 50.5% and 89.7%, respectively.ConclusionSignificant changes of ablation zones were demonstrated in a pig liver model. Considerable heat sink effect was observed within a diameter of 15mm around simulated vessels, dependent on flow rate. This has to be taken into account when ablating liver lesions close to vessels.

Microwave ablation of primary and secondary liver tumours: ex vivo, in vivo, and clinical characterisation

“…On the other side, however, slower (i.e. low power) depositions are more likely affected by blood perfusion and heat sinks in in vivo applications [23]. Delivering MW energy in vivo at intermediate power and time settings (60 W for 5 or 10 min) may therefore supply the best trade-off between ablation volume and sphericity.…”

The impact of frequency on the performance of microwave ablation

“…Most studies of MWA have been conducted at 915 MHz [8,[11][12][13][14] and 2.45 GHz [2,3,6,7,9,10,[15][16][17][18][19][20]. Similarly, most if not all commercial MWA systems to date operate at one of these two frequencies.…”

A comparison between 915 MHz and 2450 MHz microwave ablation systems for the treatment of small diameter lung metastases

“…Although microwave ablations have been shown to be less susceptible towards the heat-sink effect, its influence on the therapy success is still significant using the current generation of MWA devices (26,27). The significantly higher LTP rate after the ablation of perivascular tumors with both systems confirms these observations.…”