Examining the Current Landscape of Liver Assessment by means of Viscosity and Shear Wave Elastography: A State-of-the-Art Review.

Ultrasound plays a central role in the diagnosis, monitoring, and management of liver diseases. Assessing hepatic fibrosis is essential in chronic liver disease, and several diagnostic modalities are available. The gold standard remains percutaneous liver biopsy, an invasive method using a 16-18-gauge needle. A breakthrough came in 2003 with transient elastography (TE), a non-invasive technique that measures liver stiffness (kPa) via elastic wave propagation. Later, shear wave elastography (SWE), integrated into modern ultrasound systems, was developed to assess tissue elasticity. SWE generates shear waves (SWs) through acoustic radiation force, assuming tissues to be linearly elastic and homogeneous, and provides quantitative stiffness data. Recent evidence shows hepatic tissue is viscoelastic, with wave propagation varying by frequency. Quantifying viscosity remains a challenge. Fibrosis affects viscoelastic properties and shear wave speed (SWS), while necroinflammation predominantly alters the viscous component, influencing the shear wave dispersion slope (SWDS). This review provides an overview of ultrasound elastography methods, including stiffness and viscosity assessment, their physical principles, and clinical applications in hepatology.