Analysis of different approaches for blood oxygenation determination from multispectral optoacoustic measurements

We present the comparison of two approaches of blood oxygen saturation determination from multispectral optoacoustic measurements: a calibration-free approach based on evaluation of the effective optical attenuation coefficient derived from in-depth OA signal decay, and an approach based on determination of optical absorption coefficient from OA signal amplitudes. Both approaches were tested in in vitro and in vivo experiments. The results of in vitro and in vivo experiments demonstrated the large difference between experimentally obtained μeff spectra and the literature data, that indicates much lower potential of the OA signal decay approach as compared to OA amplitudes approach. In vivo measurements of the μa spectrum experimentally obtained from OA signal amplitudes give the saturation values of 0.57±0.08 and 0.50±0.07 for two veins of the thoracic spine that agree well with physiological values for venous blood oxygenation in rat. Instead of multiple wavelengths measurements, a pair of wavelengths can be employed for OA measurements. In this case, the saturation maps were obtained at all wavelength pairs from the 658‒1069 nm range. The results demonstrated that the most accurate oxygenation values can be achieved at wavelength pairs of 700 nm and a wavelength from the range 850-1069 nm.