Reconstruction of Viscosity Maps in Ultrasound Shear Wave Elastography

Change in viscoelastic properties of biological tissues may often be symptomatic of dysfunction that can be correlated with tissue pathology. Shear wave (SW) elastography is an imaging method mainly used to assess stiffness but with the potential to measure viscoelasticity of biological tissues. This can enable tissue characterization and, thus, can be used as a marker to improve the diagnosis of pathological lesions. In this study, a frequency-shift method-based framework is presented for the reconstruction of viscosity by analyzing the spectral properties of acoustic radiation force-induced SWs. The aim of this study was to investigate the feasibility of viscosity reconstruction maps in homogeneous as well as heterogeneous samples. Experiments were performed in four in vitro phantoms, two ex vivo porcine liver samples, two ex vivo fatty duck liver samples, and one in vivo fatty goose liver. Successful viscosity maps were reconstructed in homogeneous and heterogeneous phantoms with embedded mechanical inclusions having different geometries. Quantitative values of viscosity obtained for two porcine liver tissues, two fatty duck liver samples, and one goose fatty liver were (mean +/- SD) 0.61 +/- 0.21 and 0.52 +/- 0.35, 1.28 +/- 0.54 and 1.36 +/- 0.73, and 1.67 +/- 0.70 Pa.s, respectively.