Flow-dependent vascular heat transfer during microwave thermal ablation

Abstract

Microwave tumor ablation is an attractive option for thermal ablation because of its inherent benefits over radiofrequency ablation (RFA) in the treatment of solid tumors such as hepatocellular carcinoma (HCC). Microwave energy heats tissue to higher temperatures and at a faster rate than RFA, creating larger, more homogenous ablation zones. In this study, we investigate microwave heating near large vasculature using coupled fluid-flow and thermal analysis. Low-flow conditions are predicted to be more likely to cause cytotoxic heating and, therefore, vessel thrombosis and endothelial damage of downstream tissues. Such conditions may be more prevalent in patient with severe cirrhosis or compromised blood flow. High-flow conditions create the more familiar heat-sink effect that can protect perivascular tissues from the intended thermal damage. These results may help guide placement and use of microwave ablation technologies in future studies.

Figure 1

A) Potential of cytotoxic heat transfer in microwave tumor ablations near vessels. B) Thrombus formation during an-vivo study of high-powered microwave ablation

Figure 2

Numerical results depicting decreased heat transfer while increasing distance between applicator and vessel from A) 1 cm to 3 cm. B) Temperature map of ablation at different velocities, with the 53°C isotherm highlighted to indicate location of immediate cellular necrosis. Increasing blood velocity is associated with a decrease in intravascular heat transfer near ablation zones.

Figure 3

Phantom modeling results (n=6) demonstrating significantly higher temperature elevation (p<0.05) at 0.003 m/sec compared to all other perfusion rates at vessel locations 4-6 cm downstream from the ablation zone.