Monitoring of Thermal-Induced Changes in Liver Stiffness During Controlled Hyperthermia and Microwave Ablation in an Ex Vivo Bovine Model Using Point Shear Wave Elastography

Purpose: To investigate liver stiffness changes—evaluated by point shear wave elastography (pSWE)—in controlled hyperthermia and microwave ablation (MWA) in an ex vivo animal model. Materials and Methods: Five samples of ex vivo bovine liver were uniformly heated to temperatures ranging from 40 to 100 °C. B-mode ultrasound imaging and pSWE were acquired simultaneously, and shear wave velocity (SWV) was measured in a region of interest (ROI). The threshold value of SWV at 60 °C (avg60) was identified. Subsequently, MWA was performed in 11 liver samples at 60 W until avg60 + 0.5 m/s was reached. SWV was measured in ROIs at 10–40 mm from the antenna feed. The correlation of mean values of SWV with location (within, border, or outside necrotic area) at gross pathology was evaluated. Results: In controlled hyperthermia experiments, a steep transition in liver stiffness was observed at 63.0 ± 2.4 °C (SWV 3.54 ± 0.68 m/s). Avg60 was of 2.5 m/s. In 8/9 MWA experiments, interrupted when SWV of 3 m/s was measured, the ROI was at the inner side of the necrotic area border at pathology (accuracy 89%). No correlation between SWV values for outside, border, and within necrosis could be identified. Conclusions: pSWE can provide a velocity threshold predictive of the presence of coagulation necrosis during MWA in ex vivo liver model. However, pSWE is not able to reliably capture changes in stiffness within, at the border, and outside the necrotic zone in this experimental model.