Copolymer-in-oil phantoms for photoacoustic imaging

Photoacoustic imaging is a hybrid imaging modality, where ultrasound waves are generated from the interaction between light and biological tissue. Therefore, the image contrast is based on the optical absorption properties of tissues. A useful approach for studying photoacoustic imaging methods is through tissue-mimicking phantom experiments. Water-based materials are commonly used in phantoms for photoacoustic imaging. However, these materials have disadvantages such as easy degradation and low temporal stability. In this paper, copolymer-in-oil phantoms are presented for ultrasound and photoacoustic techniques, with the advantage of presenting low temporal degradation. Oil-based materials made of mixtures of styrene-ethylene/butylene-styrene (SEBS) and low-density polyethylene (LDPE) using paraffinic mineral oil as solvent was prepared, and annatto dye was used as optical absorber. Acoustic and optical characterization of the material was performed, where speed of sound, attenuation coefficient, optical absorption and scattering coefficients were evaluated. The phantom material showed tissue-mimicking optical and ultrasonic properties. A cubic phantom with a spherical absorber inclusion for photoacoustic imaging was manufactured. The photoacoustic signal from the inclusion showed the highest intensities at 532 nm with consistent variation for other wavelengths according to the measured absorption spectrum. In this case, the absorption spectrum acquired for the material containing annatto showed band between 350-550nm. Therefore, the results suggest the phantoms of SEBS and LDPE are promising for photoacoustic imaging.