In vivo functional microangiography by visible-light optical coherence tomography.

Although hemoglobin oxygen saturation (sO2) in the microvasculature is an essential physiological parameter of local tissue functions, non-invasive measurement of microvascular sO2 is still challenging. Here, we demonstrated that visible-light optical coherence tomography (vis-OCT) can simultaneously provide three-dimensional anatomical tissue morphology, visualize microvasculature at the capillary level, and measure sO2 from the microvasculature in vivo. We utilized speckle contrast caused by the moving blood cells to enhance microvascular imaging. We applied a series of short-time inverse Fourier transforms to obtain the spectroscopic profile of blood optical attenuation, from which we quantified sO2. We validated the sO2 measurement in mouse ears in vivo through hypoxia and hyperoxia challenges. We further demonstrated that vis-OCT can continuously monitor dynamic changes of microvascular sO2.