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Shaohua Pi, Acner Camino, Xiang Wei, William Cepurna, David Huang, John C Morrison, Yali Jia; Automated Measurement of Oxygen Saturation in Retinal Blood Vessels with Visible-light OCT. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1971.
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To automatically determine oxygen saturation (sO2) in rat retina objectively and reliably using visible-light optical coherence tomography (vis-OCT).
A 1.7-µm axial resolution, fiber-based vis-OCT system centered at 560 nm was built and used to image the retina of brown Norway rats (17 weeks old). Volumetric scans were acquired over 2.2 × 2.2 mm2 disc regions by using 3 repeated B-scans at each of 512 raster positions; each B-scan comprised of 512 A-lines. Posterior borders (bottoms) of retinal arteries and veins were automatically detected on structural OCT. Bottom pixels were spectroscopically analyzed to measure hemoglobin absorption and calculate sO2. Circular Doppler scans (d=0.9 mm) consisting of 4096 A-lines were also acquired around disc. Doppler phase shift were calculated between adjacent A-lines. Vessels identified as arteries and veins by oximetry using vis-OCT were compared to those from fundus images and Doppler OCT images (Fig. 1). The oxygen concentration in the inhalation gas was decreased from 100% to 50% and to 21%, and then back to 50% and finally 100%. Arterial sO2 (A-sO2) and venous sO2 (V-sO2) were measured and oxygen extraction (A-V sO2) were derived at the different inhaled oxygen concentrations. All experiments were repeated 4 weeks later to test inter-session reproducibility.
One eye of each rat was randomly selected and six eyes were imaged. Arteries, with a higher sO2 by vis-OCT oximetry, could be distinguished from veins. This arteriovenous distinction agreed Doppler OCT flow direction and with morphologic appearance in fundus images (Fig. 1). A-sO2 measured by vis-OCT mirrored systemic arterial oxy-hemoglobin saturation (SaO2) as determined by pulse oximetry (correlation: 0.92, p-value<0.001). In hyperoxia (100% O2) (Fig. 2 and Table 1), A-sO2 was 99% ± 1% (mean ± population standard deviation) and the V-sO2 was 87% ± 2%. In normoxia (21% O2), A-sO2 dropped to 92% and V-sO2 dropped to 69%, suggesting an increased oxygen extraction from 12% to 23%. A-sO2 and V-sO2 returned to original levels when the inhalation gas was returned to 100%. The inter-session reproducibility (pooled standard deviation) of A-sO2 and V-sO2 was good at all 3 conditions (Table 1).
Automated oximetry based on vis-OCT reliably differentiates oxygen saturation between arteries and veins and detects a greater tissue oxygen extraction at normoxia than that at hyperoxia.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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