Optical tuning of tissue-mimicking copolymer-in-oil gel for multispectral photoacoustic imaging

Background, Motivation, and ObjectiveThe demand for tissue-mimicking materials (TMMs) is increasing alongside the advancement of hybrid imaging such as photoacoustic imaging (PAI). Developing suitable TMMs for PAI is challenging due to the need to mimic both optical and acoustic tissue properties. The TMMs with tunable properties are needed for the calibration of these imaging modalities, as well as the development and assessment of new quantitative methods and clinical training in applying quantitative PAI. This study aimed to develop and characterize long-lasting TMMs by mixing a styrene-ethylene/butylene-styrene (SEBS) copolymer and mineral oil, and using this SEBS-gel, assessing their fabrication, stability, and control of optical properties, while also describing the novel manufacturing process.Statement of Contribution/MethodsA TMM was fabricated by mixing a SEBS copolymer and mineral oil, supplemented with artists’ oil-based ink dissolved and diluted in balsam turpentine to tune its optical absorption independently. Next, the optical and acoustic properties of this TMM with various concentrations of oil-based inks (carbon black, prussian blue, light green, and rubine magenta) such as optical absorption, optical scattering, speed of sound, and acoustic attenuation were investigated. PAI was conducted using the VisualSonics Vevo LAZR-X imaging platform within the 680–970 nm wavelength range. The photoacoustic amplitude at each wavelength was then averaged over the specific region of interest to compute the spectrum. Finally, the potential of these PAI phantoms employing TMMs comprising mineral oil SEBS gel with oil-based inks as additives for preparing heterogeneous smiley phantoms was studied.Results/DiscussionFigure a shows the PAI on the oil-based ink SEBS-gel in prussian blue, which proved effective in tuning the optical absorption properties of mineral oil SEBS-gel with high accuracy. Figure b shows the optical extinction coefficient of the same phantom series with increasing mass fraction of the oil-based inks. TMMs Incorporating oil-based inks into SEBS gel had a negligible impact on the speed of sound. However, the acoustic attenuation coefficient decreased with increasing mass fractions of two of the oil-based inks (carbon black and light green). Pure SEBS gel yielded minimal photoacoustic signal whereas SEBS gel with added oil-based inks exhibited distinct photoacoustic spectra, indicating significant potential for future use as photoacoustic phantom material. Increasing the mass fraction of oil-based inks led to higher photoacoustic amplitude without affecting the spectral shapes, as the amplitude increased linearly with the oil-based ink mass fraction (Figure c). Figure d shows a photograph of one smiley phantom, and Figure (e) presents the results of spectral unmixing on the corresponding phantom. These findings suggest that this TMM facilitates the development of more sophisticated phantoms of arbitrary shapes. The TMMs demonstrated long-term stability and suitability for producing phantoms that could be stored at room temperature without requiring special storage conditions.