Effects of wavelength-dependent fluence attenuation on the noninvasive photoacoustic imaging of hemoglobin oxygen saturation in subcutaneous vasculature in vivo

Due to wavelength-dependent optical attenuation in the skin, the local fluence at a subcutaneous vessel varies with the optical wavelength in a spectral measurement. Hence compensation for such a spectral attenuation is necessary in quantitative measurements of the oxygen saturation of hemoglobin (sO_2) in blood vessels in vivo using photoacoustic (PA)imaging. Here, by employing a simplified double-layer skin model, we find that although the absolute value of sO_2 in a vessel is seriously affected by the volume fraction of blood and the spatially averaged sO_2 in the dermis, the difference of sO_2 between neighboring vessels is minimally affected. Based on in vivo experiments, we demonstrate that the difference in sO_2 between a typical artery and a typical vein is conserved before and after an experimentally acquired spectral compensation. This conservation holds regardless of the animal's systemic physiological state.