Optical properties of blood at various levels of oxygenation studied by time-resolved detection of laser-induced pressure profiles

Time resolved detection of laser-induced pressure profiles permits sensitive and high-resolution measurements of distribution of absorbed optical energy in optically scattering and opaque media, such as blood. We report experimental measurements of optical properties in the whole blood of animals at various levels of oxygen saturation and analytical calculations of relative concentrations of oxy- and deoxy- hemoglobin. The results show that optoacoustic profiles are sensitive to small variations in optical properties of blood. When measured with absolutely calibrated acoustic transducers at two different laser wavelengths, 757-nm and 1064-nm, the total hemoglobin concentration and its oxygenation level can be determined from the optoacoustic profiles. The value of thermoacoustic efficiency of pressure wave generation by laser irradiation was also determined from experiments. Erythrocyte sedimentation and aggregation rate was studied, since these phenomena affect spatial distribution of optical energy in blood upon laser irradiation. Erythrocyte sedimentation rate was calculated from kinetic changes in optoacoustic profiles. The results encourage development of various applications of optoacoustic spectroscopy in monitoring of blood properties in vitro and in human tissues.