Optical and acoustic characterization of freeze-thawed polyvinyl alcohol gels

Preclinical validation of non-invasive photoacoustic imaging of carotid artery atherosclerosis requires vessel phantoms that imitate optical, acoustic and mechanical properties of vascular tissue. Polyvinyl alcohol (PVA) phantoms that are widely used as ultrasound phantoms due to their elastic properties are also promising for photoacoustics. This study contributes to the field by quantifying the optical and acoustic properties of PVA gel, and aims at the characterization of realistic phantoms for future studies. In this study, we investigated the relation between acoustic scatterers and optical absorbers to quantify optical and acoustic properties of the PVA phantoms. Four different concentrations of orgasol acoustic scatterers, and varying concentration of Indian ink and molecular dye absorbers were added to a 15 wt% PVA solution. Samples were subjected to 1 to 5 freeze-thaw cycles and were examined after each cycle to quantify the effect on the optical and the acoustic properties. Optical attenuation was measured between 400 nm and 990 nm using a plate reader. Additionally, pulse-echo plane wave ultrasound was used for acoustic characterization. Changing the concentration of orgasol between 0.5 wt% and 4 wt% increased the mean optical attenuation of PVA by 35% after the first freeze thaw cycle. Likewise, each freeze-thaw cycle increased the optical attenuation due to scattering of light by the microstructure of PVA. The absorbance of pure PVA increased 40% between the first and second cycle and 3% between the fourth and fifth cycle. While the orgasol concentration and the freeze-thaw cycles altered the acoustic speed and attenuation, the ink and the dye inclusions did not significantly affect the acoustic properties of PVA.