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-mimicking material 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 alpha(f) were characterised over 2-10 MHz; optical absorption mu(a)(lambda) and reduced scattering mu(s)'(lambda) 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-stability were studied, along with intra-laboratory fabrication and field-testing. c( f) could be tuned up to (1516 +/- 0.6)m.s(-1) and alpha(f) to (17.4 +/- 0.3)dB.cm(-1) at 5 MHz. The base material exhibited negligible mu(a)(lambda) and mu(s)'( lambda), 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), alpha (f), optical transmittance and reflectance), and good photo- and mechanical-stability in the relevant working range (20-40 degrees C). The optimised copolymer-in-oilmaterial represents an excellent candidate for widespread application in PAI phantoms, with properties suitable for broader use in biophotonics and ultrasound imaging standardisation efforts.