Ultrasound shear wave elastography for evaluation of boundary of liver lesions ablated with microwave

Abstract

Objective To explore the feasibility and accuracy of ultra-high speed shear wave elastography (SWE) in quantitative evaluation of the boundary of liver lesions ablated with microwave. Methods Fifteen healthy five-month-old Wuzhishan pigs weighing (15±0.5) kg underwent microwave ablation under an open laparotomy. The ablation power was selected at 40 W, and the ablation time was set at 15 s, 30 s, and 60 s. Immediately after ablation, SWE was used to measure the elastic modulus of the lesion. The degree of liver tissue damage was assessed by HE staining and nicotinamide adenine dinucleotide (NADH)-diaphorase histochemical staining. Results In the study, 156 effective ablation procedures were performed, 740 effective SWE measurements were performed, and 131 effective pathological results were obtained. The elastic modulus of the lesions was distributed in a regional stepped concentric circle, which can be divided into three regions from the center to the outer circumference. At the same ablation time, the elastic modulus value increased stepwise from the surrounding normal tissue region to the ablation boundary region and ablation center region (P 0.05), regardless of the ablation time (15 s, 30 s, and 60 s); however, the elastic modulus values in the ablation region showed a significantly stepwise decrease with the decrease in the ablation time [60 s: (97.16±14.58) kPa, 30 s: (77.84±9.64) kPa, 15 s: (38.92±3.12) kPa; F=2131.832, P<0.01]. The elastic modulus values of the ablation boundary regions at different ablation time points were maintained at 22.68 to 23.56 kPa. Conclusion The range of elastic modulus in the boundary region of microwave ablated lesions is relatively fixed. SWE can help quantitatively evaluate the effective damage range and type of liver microwave ablation, and has practical value in monitoring and evaluation of microwave ablation. Key words: Elasticity imaging techniques; Shear wave; Microwaves; Ablation techniques; Elastic modulus; Liver