Transmission-Based Monitoring of Dual-Applicator Microwave Ablation Discriminates Discontiguous from Contiguous Ablation Zones in an In Vivo Porcine Liver Model.

Abstract

Purpose: To determine the technical feasibility of discriminating discontiguous from contiguous ablation zones between a pair of microwave ablation (MWA) applicators using broadband microwave transmission signal measurements in an in vivo porcine liver model.

Methods: Dual applicator 2.45GHz MWA was performed using one directional and one omnidirectional applicator, spaced 3cm apart, under imaging guidance. The study involved 15 hepatic MWAs across four swine, with ablation durations of 200s (n=8) for discontiguous ablation and 600s (n=7), each at 60W; these ablation durations and applied power combinations were selected with the intent of creating discontiguous (200s) and contiguous (600s) ablation zones. A custom software periodically measured transmission signals between the applicators at 46-second intervals. Contrast-enhanced CT, gross pathology, and histopathologic analyses were used to assess the processed transmission signal (PTS).

Results: Statistical analyses revealed significant differences between contiguous and discontiguous ablation zones on CECT imaging (volume: 16.9±5.2cm³ vs. 3.9±1.5cm³, p=0.0002), gross tissue sections and histology (area: 10±3.3cm² and 6.5±1.3cm², p=0.001 and PTS datasets showed values of 85.1±11% and 37.3±12.9% (p=0.02). PTS values functioned well as predictors of complete vs incomplete ablation (area under curve of the receiver operating characteristic curve = 0.90), with a PTS threshold of 53% being optimal for indicating ablation zone contiguity. Ablation zone contiguity was strongly correlated with PTS (Spearman correlation coefficient 0.86, p<0.0001).

Conclusion: This study demonstrated that PTS between dual MWA applicators can distinguish between contiguous and discontiguous ablation zones.