Acoustoelasticity in transversely isotropic soft tissues: Quantification of muscle nonlinear elasticity

International audienceRecent developments in the field of elastography aim at developing the quantification of new mechanical propertiesof tissues, that are complementary to the shear modulus, which is characteristic of the linear elastic properties of aquasi-incompressible medium. In this context, measurement of the elastic nonlinearity of tissues was recently proposedbased on acoustoelasticity. Up to now, most of the experimental applications of acoustoelasticity theory usingLandau formalism in human tissues have assumed isotropy. However, this strong hypothesis does not hold in allhuman tissues, such as muscles that are generally considered as transversely isotropic (TI). In this work, afterreviewing the constraints imposed by TI symmetry on the linear and nonlinear elastic properties of TI media, theacoustoelasticity theory in TI incompressible media is developed and implemented experimentally on a TI polyvinylalcohol phantom and on ex vivo muscular tissues. Based on this theory and on the evolutions of the shear wavespeed, with respect to uniaxial static stress, the nonlinear elastic parameter A is experimentally quantified. The estimationsof A in ex vivo bovine and porcine muscles are on the order of hundreds of kPa. This work paves the wayfor more thorough muscle mechanical properties characterization as well as for the development of a potential newbiomarker