Noninvasive monitoring of cerebral blood oxygenation in ovine superior sagittal sinus with novel multi-wavelength optoacoustic system

Noninvasive monitoring of cerebral blood oxygenation with an optoacoustic technique offers advantages over current invasive and noninvasive methods. We report the results of in vivo studies in the sheep superior sagittal sinus (SSS), a large central cerebral vein. We changed blood oxygenation by increasing and decreasing the inspired fraction of oxygen (FiO₂). Optoacoustic measurements from the SSS were performed at wavelengths of 700, 800, and 1064 nm using an optical parametric oscillator as a source of pulsed near-infrared light. Actual oxygenation of SSS blood was measured with a CO-Oximeter in blood samples drawn from the SSS through a small craniotomy. The amplitude of the optoacoustic signal induced in the SSS blood at λ = 1064 nm closely followed the changes in blood oxygenation, at λ = 800 nm was almost constant, and at λ = 700 nm was changing in the opposite direction, all in accordance with the absorption spectra of oxy- and deoxyhemoglobin. The optoacoustically predicted oxygenation correlated well with actual blood oxygenation in sheep SSS (R² = 0.965 to 0.990). The accuracy was excellent, with a mean difference of 4.8% to 9.3% and a standard deviation of 2.8% to 4.2%. To the best of our knowledge, this paper reports for the first time accurate measurements of cerebral venous blood oxygenation validated against the "gold standard" CO-Oximetry method.