Quantitative techniques for extraction of blood oxygenation from multispectral optoacoustic measurements

We report on the comparison of two approaches to the reconstruction of oxygen saturation (StO₂) within blood vessels from multispectral optoacoustic (OA) measurements. The spatially-resolving approach is based on determination of the optical absorption coefficient µ _a from OA signal amplitudes, while the calibration-free approach is based on evaluation of the effective optical attenuation coefficient µ _eff derived from the in-depth OA signal decay. Both approaches were verified in phantom experiments as well as in in vitro and in vivo measurements. The results demonstrate good agreement of µ _a spectra derived from OA signal amplitudes with the published data indicating this approach to be preferable for the in vivo determination of StO₂. Reconstruction of µ _a spectra from the in vivo measured OA signal amplitudes in a rat yields StO₂ values of 0.57  ±  0.08 and 0.50  ±  0.07 for two veins of the thoracic spine. We demonstrate that for cost-effective measurements a dual-probing wavelength scheme can be employed instead of multiple wavelength probing. We found that the probing wavelength of 700 nm combined with a wavelength from the range of 850–1069 nm provides reconstructed StO₂ values close to the reference ones derived from multiple wavelength measurements in the entire range of 658‒1069 nm. (letter)