03:27 PM Abstract No. 366 Quantification of the heat-sink effect during microwave ablation with 4D-flow MRI in an in-vivo porcine liver model

Abstract

Image-guided thermal ablation has become the standard of care for treating early stage liver cancer. However, a significant limitation to a successful ablation procedure is the heat-sink effect, which may lead to suboptimal thermal dose delivery. Currently, there is no reliable method for quantifying the heat-sink effect due to limited information on blood vessel flow and its associated anatomy relative to the ablation zone. The purpose of this study was to use 4D-flow MRI to map out liver flow patterns and correlate flow rates with ablation zone volumes. Female domestic swine (n=3) were anesthetized and prepared as per IACUC guidelines. A subject-specific map of the hepatic vasculature was generated via 4D-flow MRI. Microwave ablation zones were created in individual liver lobes near major vessels by applying 65 W for 5 minutes through a high-powered microwave antenna. For each ablation zone, the pre-ablation and post-ablation flow rates (mL/sec) of the encompassed vessels, as well as their corresponding ablation sizes (mL) were recorded and analyzed via logistic regression modeling and Student t-test. A total of n=9 ablation zones were created that encompassed individual portal and hepatic veins. There were 3/6 (50%) thrombosed portal veins and 0/8 (0%) thrombosed hepatic veins (p=0.21). Hepatic vein flow rate decreased significantly after ablation (2.3±0.7 mL/sec vs 1.5 ±0.4 mL/sec, p=0.01). Portal vein flow rate similarly decreased (2.1±0.9 mL/sec vs 1.8±1.1 mL/sec, p=0.72) after ablation, although not significantly so. Ablation zones that encompassed vessels with flow rates > 2.0 mL/sec were significantly smaller in volume than ablation zones encompassing vessels with flow rates < 2.0 mL/ sec (4.2±3.0 mL vs 9.3±2.5 mL, p=0.03). Microwave ablation zones were found to be significantly smaller in volume when encompassing vessels with flow rates greater than 2.0 mL/sec. Both portal veins and hepatic veins show decreased flow in ablation zones, likely relating to their response to thermal damage. Mapping out blood flow vasculature with 4D-flow MRI prior to ablation zones can assist clinicians in deciding how aggressively to treat liver tumors.