Imaging of hemoglobin oxygen saturation variations in single vessels in vivo using photoacoustic microscopy

Photoacoustic microscopy was used to noninvasively image variations in hemoglobin oxygen saturation $\left(\mathrm{S}{\mathrm{O}}_2\right)$ in the subcutaneous microvasculature of rats in vivo. In phantom tests, the calculated concentration fractions of red ink in double-ink mixtures matched the actual values with a 1% error. In ex vivo studies, the calculated $\mathrm{S}{\mathrm{O}}_2$ in bovine blood agreed with the standard spectrophotometric measurements within a 4% systematic difference. In in vivo studies, arteries and veins were separated based on the measured $\mathrm{S}{\mathrm{O}}_2$ values and variations in $\mathrm{S}{\mathrm{O}}_2$ between different physiological states (hyperoxia, normoxia, and hypoxia) were imaged in single blood vessels.