Temperature dependence of the shear modulus of soft tissues assessed by ultrasound

Ultrasound-based techniques to monitor HIFU treatments, combining temperature and elasticity mapping, require better understanding of the thermal effects on soft tissues elasticity. Hence, the study aims to evaluate the temperature dependence of the shear modulus of bovine muscles. Nine ex vivo samples of bovine muscle were slowly heated into a thermally-controlled saline bath. Thermocouples were used to assess temperatures into muscles. Local elasticity was assessed using Supersonic Shear Imaging. Samples were heated from 20°C to 70°C by steps of 10°C and 20 min long and cooled back at room temperature. Elasticity assessment was achieved every minute along the muscular fibres. The shear modulus decreased linearly with increasing temperature up to 44°C, with a change in slope around 37°C. Then, it exponentially decreased from 44°C to 56°C. Finally, it exponentially increased for higher temperatures. The thermal-induced changes in the shear modulus of ex vivo bovine muscles using ultrasound are consistent with theoretical changes of myosin and collagen microstructure. Given the high sensitivity of the ultrasound-based technique to the behaviour of both myofibrilar proteins and collagen on heating, this study gives promising prospects for the use of a full-ultrasound-based technique to monitor thermal effects on tissues.