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
$\alpha $

(f)
were characterised over 2–10 MHz; optical absorption
$\mu _{\mathrm {a}}$
(
$\lambda $
) and reduced scattering
$\mu _{\mathrm {s}}$
’(
$\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-stabilitywere studied, alongwith intra-laboratory fabrication and field-testing.
c(f)
could be tuned up to (1516±0.6)
$\text{m}\cdot \text{s}^{-1}$
and
$\alpha $

(f)
to (17.4±0.3)dB
$\cdot $
cm
$^{-1}$
at 5 MHz. The base material exhibited negligible
$\mu _{\mathrm {a}}$
(
$\lambda $
) and
$\mu _{\mathrm {s}}$
’(
$\lambda $
), which could be independently tuned by addition of Nigrosin or TiO
₂
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°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.