Real-time control of bulk ultrasound thermal ablation using echo decorrelation imaging feedback

Abstract

In this study, the feasibility of controlling bulk ultrasound (US) thermal ablation using echo decorrelation imaging feedback was assessed in ex vivo bovine liver. US exposures (5–5.4 MHz, 8.2–8.5 s/cycle, 70–73% duty, 31–41 W/cm2 spatial-peak, temporal-peak intensity) and echo decorrelation imaging were performed by a linear image-ablate array. Preliminary experiments (N=86) were carried out to optimize a control region of interest (ROI) and determine the ablation control threshold. In controlled trials (N=13), 9 sonication cycles at 31.5 W/cm2 were followed by up to 9 cycles at 35.3 W/cm2, with treatments ending when the average cumulative echo decorrelation within the ROI exceeded the selected threshold. Controlled trials were compared with uncontrolled trials employing 9 (N=10) or 18 (N=10) cycles of the same sonication sequence. Resulting lesion dimensions and areas under receiver operating characteristic (ROC) curves (AUC) were statistically compared. The control threshold was selected as −1.576 (log 10 -scaled decorrelation per ms), and was exceeded in 10 of the 13 controlled trials. Successfully controlled trials showed significantly greater average lesion area (3.66 cm2) and depth (14.7 mm) than 9-cycle (2.14 cm2, p=3×10−4; 8.3 mm, p=2×10−4) uncontrolled trials, less treatment time (113.1 s) than 18-cycle (147.6 s, p=2×10−5) uncontrolled trials, and greater prediction capability (AUC=0.858) than the combined 20 uncontrolled trials (AUC=0.628). These results indicate that echo decorrelation imaging is an effective approach to bulk US ablation control.