Characterization of tissue-mimicking polyvinyl alcohol phantoms for shear wave viscoelastography: effects of aluminum oxide and cryoprotectant concentration

Introduction Polyvinyl alcohol (PVA) phantoms are under development for quality control and evaluation of shear wave elastography. These are typically formulated with aluminum oxide to mimic soft-tissue attenuation. Further, cryoprotectants, such as ethylene glycol (EG) and propylene glycol (PG), suppress ice crystal formation during freeze-thaw cycling and improve homogeneity. This study systematically assesses the effects of aluminum oxide and the cryoprotectants EG and PG on the acoustic and viscoelastic properties of PVA phantoms for elastography applications. Methods Phantoms were fabricated from 10% (w/v) PVA, with aluminum oxide varied from 0%–10% (w/v), and with EG or PG varied from 0%–20% (v/v). Microstructure was examined by scanning electron microscopy. Density, longitudinal sound speed, and attenuation were measured for each phantom (n = 5 each). Shear-wave viscoelastography was performed to estimate shear modulus and viscosity. Results Longitudinal sound speed (1576–1583 m/s) and viscosity (1.58–2.15 Pa s) did not change significantly with increasing aluminum oxide concentration. On the other hand, attenuation increased from 0.12–0.54 dB/cm/MHz (r = 0.98; p < 0.001), density rose from 1.03–1.14 g/cm 3 (r = 0.91, p < 0.001), and shear modulus increased from 3.05 to 5.32 kPa (r = 0.79; p < 0.001). Longitudinal sound speed and attenuation measurements increased with increasing cryoprotectant concentration. Sound speed measurements spanned 1535–1643 m/s for EG (r = 0.99, p < 0.001) and 1535–1666 m/s for PG (r = 0.99; p < 0.001). Attenuation spanned 0.27–0.40 dB/cm/MHz for EG (r = 0.84; p < 0.001) and 0.27–0.39 dB/cm/MHz for PG (r = 0.82; p < 0.001). Shear modulus estimates changed non-monotonically with cryoprotectant concentration, decreasing from 6.94 kPa at 0% EG to 3.81 kPa at 15%, and increasing to 8.01 kPa at 20%. The shear modulus decreased from 0% to 10% PG and remained constant from 10% to 20%. Viscosity decreased from 0%–5% but was not significantly different between 5%-20% for both EG and PG phantoms. Discussion Aluminum oxide doping simultaneously increases attenuation and alters viscoelastic properties, while cryoprotectants drive nonlinear shifts in mechanical properties. These results demonstrate how the additives concomitantly influence the acoustic and viscoelastic properties of PVA phantoms. These findings support efforts to standardize phantom fabrication protocols and control confounding variables.