Quantitative viscoelastic assessment of copolymer-in-oil tissue-mimicking phantoms using plane-wave and ARFI-induced shear wave elastography.

Tissue-mimicking phantoms play a crucial role in evaluating new imaging modalities, simulating clinical scenarios, and ensuring the quality and reliability of imaging systems. Styrene-ethylene/butylene-styrene (SEBS) is an extremely stable and versatile material that has been recently used in ultrasound, elastography, and photoacoustic imaging across diverse applications. Despite its extensive use, a systematic viscoelastic characterization of different SEBS-based formulations reported in the literature, particularly using shear wave elastography (SWE), remains limited. To address this gap, this study investigates the viscoelastic properties of tissue-mimicking phantoms composed of SEBS, glycerol dispersions in SEBS gels, and mixtures of SEBS with low-density polyethylene (LDPE) in mineral oil, using gelatin phantoms as a reference for comparison. Viscoelastic parameters were estimated from shear wave velocity and attenuation dispersion curves using a Kelvin-Voigt model, based on SWE measurements with acoustic radiation force (ARF) excitation, shear plane-wave excitation, and complementary mechanical testing. SEBS-based phantoms exhibited broad, composition-dependent viscoelastic tunability. Increasing SEBS or LDPE content led to stiffer and more viscous responses, while glycerol primarily modulated viscosity and, at higher concentrations, also affected stiffness. Consistent and concordant values were obtained using both ARF and plane wave SWE techniques. The resulting stiffness (2-22 kPa) and viscosity (0.01-1.24 Pa⋅s) overlaps with the mechanical properties of several biological soft tissues, supporting use of these phantoms for SWE validation.