A copolymer-in-oil tissue-mimicking material with tuneable acoustic and optical characteristics for photoacoustic imaging phantoms

Photoacoustic imaging (PAI) standardisation demands a stable, highly reproducible physical phantom to enable routine quality control and robust performance evaluation. To address this need, we have optimised a low-cost copolymer-in-oil tissue-mimickingmaterial formulation. The base material consists of mineral oil, copolymer and stabiliser with defined Chemical Abstract Service numbers. Speed of sound c(f) and acoustic attenuation coefficient α (f) were characterised over 2-10 MHz; optical absorption μ a ( λ ) and reduced scattering μ s '( λ ) coefficients over 450-900 nm. Acoustic properties were optimised by modifying base component ratios and optical properties were adjusted using additives. The temporal, thermomechanical and photo-stabilitywere studied, alongwith intra-laboratory fabrication and field-testing. c(f) could be tuned up to (1516±0.6) ms-1 and \α (f) to (17.4±0.3)dB cm -1 at 5 MHz. The base material exhibited negligible μ a ( λ ) and μ s '( λ ), which could be independently tuned by addition of Nigrosin or TiO2 respectively. These properties were stable over almost a year and were minimally affected by recasting. The material showed high intra-laboratory reproducibility (coefficient of variation <4% for c ( f), α (f), optical transmittance and reflectance), and good photo- and mechanical-stability in the relevant working range (20-40°C). The optimised copolymer-in-oil material represents an excellent candidate for widespread application in PAI phantoms, with properties suitable for broader use in biophotonics and ultrasound imaging standardisation efforts.