Application of acoustoelasticity to evaluate non-linear modulus in ex vivo kidneys

Dynamic elastography techniques estimate the elastic shear modulus in order to evaluate the health of different soft tissues. However, the diagnostic potential of these methods is limited as the knowledge of shear elasticity may not be sufficient to reach a clinical diagnosis. To better understand pathologies, new methods that investigate non-linear tissue mechanical properties have been proposed. It has previously been shown that shear wave speed changes with respect to an applied stress, a phenomenon called acoustoelasticity (AE). Using AE by compressing a medium and measuring the shear wave speed at different compression levels, we can estimate the third order non-linear modulus, A. The goal of this study was to evaluate the feasibility of performing AE in ex vivo kidneys. We evaluated the non-linear characteristics of ten ex vivo porcine kidneys embedded in 10% gelatin. Measurements were performed under three different conditions: a) presence or absence of a plate attached to the transducer, b) progressive or regressive compression and (c) views of the kidney (longitudinal and transverse). The results obtained demonstrated that it is possible to recover the non-linear modulus A by monitoring changes in strain and shear modulus during kidney deformation.