• point shear-wave elastography
• liver stiffness changes
• ex-vivo bovine liver tissue
• thermal effects

Purpose: In point shear wave elastography (pSWE), an acoustic radiation force impulse is used to generate shear ­waves in liver tissue. Shear wave velocity (SWV) reflects the underlying tissue stiffness. This study aims to (1) quantify the temperature dependence of liver tissue stiffness as measured with SWV (2) assess the repeatability of this measurement and (3) evaluate the irreversibility of stiffness changes.
Material and methods: Five samples of ex-­vivo bovine liver tissue were uniformly heated to target temperatures ranging 40°­-100°C and then cooled-down until 50°C was reached. B-­mode imaging and pSWE were acquired simultaneously (Virtual TouchTM Tissue Quantification, Siemens Healthcare) and SWV, expressed in m/s, was measured in a fixed region of interest (ROI, < 1cm2) at set temperatures (2.5-­5°C intervals). Tissue temperature was recorded by two thermocouples positioned at 1.5 cm from the ROI.
Results: A steep transition in liver stiffness was observed at 63.0±2.4°C with an average SWV value of 3.54±0.68 m/s (baseline value: 1.41±0.17 m/s at room temperature). A decrease in SWV was observed up to 42°C (­0.31±0.07 m/s with respect to baseline), a gradual increase was detected up to 55-­60°C and the described transition followed above 60°C. This pattern was observed in all experiments, with very similar SWV/temperature curves.
The changes in liver stiffness proved to be irreversible, as average SWV values of 4.40±0.41 m/s were measured in the cool­-down cycles.
Conclusion: Liver tissue stiffness is strongly affected by temperature changes. pSWE is a highly reproducible, non­-invasive technique that allows to assess ­in real-­time­ thermal effects on liver tissue.