In vivo depth-resolved oxygen saturation by dual-wavelength photothermal (DWP) OCT

Microvasculature hemoglobin oxygen saturation (SaO₂) is important in the progression of various pathologies. Non-invasive depthresolved measurement of SaO₂ levels in tissue microvasculature has the potential to provide early biomarkers and a better understanding of the pathophysiological processes allowing improved diagnostics and prediction of disease progression. We report proof-of-concept in vivo depth-resolved measurement of SaO₂ levels in selected 30 μm diameter arterioles in the murine brain using Dual-Wavelength Photothermal (DWP) Optical Coherence Tomography (OCT) with 800 nm and 770 nm photothermal excitation wavelengths. Depth location of back-reflected light from a target arteriole was confirmed using Doppler and speckle contrast OCT images. SaO₂ measured in a murine arteriole with DWP-OCT is linearly correlated (R²=0.98) with systemic SaO₂ values recorded by a pulse-oximeter. DWP-OCT are steadily lower (10.1%) than systemic SaO₂ values except during pure oxygen breathing. DWP-OCT is insensitive to OCT intensity variations and is a candidate approach for in vivo depth-resolved quantitative imaging of microvascular SaO₂ levels.