Monitoring heat-induced changes in soft tissues with 1D transient elastography

In this paper 1D transient elastography was employed in fresh bovine skeletal muscle samples to assess the shear elastic modulus μ while the tissue was locally heated by means of an electrical resistance. The investigation is based on the study of the time shift of the shear wave propagation produced by the local temperature variation. The experiments show that the thermal expansion contribution to the time shift is negligible when compared with the shear wave speed variation. In such a case, the quantification of μ as a function of temperature becomes possible. Repeated experiments in different samples lead to a reproducible behavior of μ as a function of temperature. Irreversible elasticity changes are produced when the temperature exceeds a certain critical value Tc. The proposed method allows estimating this value as well as the spatial extension of the resulting thermal lesion. This point is important when considering applications in monitoring focused ultrasound surgery (FUS) because the surrounding normal tissue should remain unaffected.