Evaluation of Absorbing Chromophores Used in Tissue Phantoms for Quantitative Photoacoustic Spectroscopy and Imaging

In this paper, the optical properties of absorbing compounds that are often used to construct tissue phantoms for quantitative photoacoustic spectroscopy and imaging are investigated. The wavelength dependence of the optical absorption of inorganic chromophores, such as copper and nickel chloride, and organic chromophores, such as cyanine-based near infrared dyes, was measured using transmittance spectroscopy and compared with that determined using photoacoustic spectroscopy. In addition, the relative change in the Grüneisen coefficient of these solutions with concentration was determined. The sound speed of aqueous gels and lipid emulsions as a function of concentration was also measured. It was found that copper and nickel chloride are suitable chromophores for the construction of photoacoustic tissue phantoms due to their photostability. By contrast, organic dyes were found unsuitable for quantitative photoacoustic measurements due to optically induced transient changes to their absorption spectrum and permanent oxidative photobleaching.