title: Assessment of viscous and elastic properties of sub-wavelength layered soft tissues using shear wave spectroscopy: theoretical framework and in vitro experimental validation.
abstract: In elastography, quantitative imaging of soft tissue elastic properties is provided by local shear wave speed estimation. Shear wave imaging in a homogeneous medium thicker than the shear wavelength is eased by a simple relationship between shear wave speed and local shear modulus. In thin layered organs, the shear wave is guided and thus undergoes dispersive effects. This case is encountered in medical applications such as elastography of skin layers, corneas, or arterial walls. In this work, we proposed and validated shear wave spectroscopy as a method for elastic modulus quantification in such layered tissues. Shear wave dispersion curves in thin layers were obtained by finite-difference simulations and numerical solving of the boundary conditions. In addition, an analytical approximation of the dispersion equation was derived from the leaky Lamb wave theory. In vitro dispersion curves obtained from phantoms were consistent with numerical studies (deviation <1.4%). The least-mean-squares fitting of the dispersion curves enables a quantitative and accurate (error < 5% of the transverse speed) assessment of the elasticity. Dispersion curves were also found to be poorly influenced by shear viscosity. This phenomenon allows independent recovery of the shear modulus and the viscosity, using, respectively, the dispersion curve and the attenuation estimation along the propagation axis.
authors.affiliation: Institut Langevin Ondes et Images, Ecole Supérieure de Physique et de Chimie de Paris (ESPCI, ParisTech), Paris, France. thu-mai.nguyen@espci.fr
authors.forename: Thu-Mai
authors.initials: TM
authors.lastname: Nguyen
authors.forename: Mathieu
authors.initials: M
authors.lastname: Couade
authors.forename: Jeremy
authors.initials: J
authors.lastname: Bercoff
authors.forename: Mickael
authors.initials: M
authors.lastname: Tanter
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D003238:Connective Tissue / Q000000981:diagnostic imaging* / Q000502:physiology*; D055119:Elastic Modulus / Q000502:physiology; D054459:Elasticity Imaging Techniques / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008954:Models, Biological; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014783:Viscosity