Photoacoustic Detection of Protein Coagulation in Albumen-based Phantoms

Photoacoustic tomography provides good optical contrast with high spatial resolution making it an attractive tool for noninvasive imaging. While the mechanical parameters of tissue affect the photoacoustic signal, the differences in optical absorption mainly determines the contrast between different media. In this work we investigate how the variation in optical and mechanical properties during laser-induced coagulation can be detected by changes in the amplitude and temporal characteristics of photoacoustic signals. Photoacoustic pressure profiles are investigated for tissue equivalent albumen phantoms exposed to varying thermal doses, simulating thermal coagulation. Illumination is performed using an optical parametric oscillator (OPO) fed by a Q-switched Nd:YAG pulsed laser to illuminate at multiple wavelengths. The results of the study demonstrate that photoacoustic signals are sensitive to changes in delivered thermal dose and, hence, photoacoustic imaging has potential as a non-invasive monitoring tool for thermal therapy.