Photoacoustic measurement of the Gruneisen parameter of tissue

The Gruneisen parameter, a constitutive parameter in photoacoustics, is usually measured from isobaric thermal expansion, which may not be valid for a biological medium due to its heterogeneity. Here, we directly measured the Gruneisen parameter by applying photoacoustic spectroscopy. Laser pulses at wavelengths between 460 and 1800 nm were delivered to tissue samples, and photoacoustic signals were detected by flat water-immersion ultrasonic transducers. Least-squares fitting photoacoustic spectra to molar optical absorption spectra showed that the Gruneisen parameter was 0.81 +/- 0.05 (mean +/- SD) for porcine subcutaneous fat tissue and 0.69 +/- 0.02 for porcine lipid at room temperature (22 degrees C). The Gruneisen parameter of a red blood cell suspension was linearly related to hemoglobin concentration, and the parameter of bovine serum was 9% greater than that of water at room temperature. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)