Temperature-dependent optoacoustic response and transient through zero Grüneisen parameter in optically contrasted media

Non-invasive optoacoustic mapping of temperature in tissues with low blood content can be enabled by administering external contrast agents. Some important clinical applications of such approach include temperature mapping during thermal therapies in a prostate or a mammary gland. However, the technique would require a calibration that establishes functional relationship between the measured normalized optoacoustic response and local tissue temperature. In this work, we investigate how a key calibration parameter – the temperature of zero optoacoustic response (T(0)) – behaves in different environments simulating biological tissues augmented with either dissolved or particulate (nanoparticles) contrast agents. The observed behavior of T(0) in ionic and molecular solutions suggests that in-vivo temperature mapping is feasible for contrast agents of this type, but requires knowledge of local concentrations. Oppositely, particulate contrast agents (plasmonic or carbon nanoparticles) demonstrated concentration-independent thermal behavior of optoacoustic response with T(0) defined by the thermoelastic properties of the local environment.