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Siyu Chen, Xiao Shu, Ji Yi, Amani A Fawzi, Hao F Zhang; Dual-band optical coherence tomography using a single supercontinuum laser source. Invest. Ophthalmol. Vis. Sci. 2016;57(12):471.
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© ARVO (1962-2015); The Authors (2016-present)
Though blood oxygen saturation (sO2) is a vital physiological indicator, OCT using near infrared (NIR) may not measure it accurately. Visible (Vis-) OCT can address the problem. However, concerns over its imaging capability still remains. We seek to answer this question by construction a dual-band OCT system, comparing them side-by-side.
A supercontinuum laser served as light source. We separated and delivered visible and NIR light to two interferometers. We employed free-space configuration for the visible interferometer. The NIR-OCT used the traditional fiber-based design. The two beams were recombined before entering the scanning mechanism, so the images were co-registered.We imaged mouse retina in vivo. In addition to structure images, we generated OCT angiography using complex de-correlation. Dual-ring scanning allowed us to measure retinal blood flow. Finally, we used spectral fitting to extract (sO2) from major retina vessels.
Our Vis- and NIR-OCT subsystems achieved depth resolution of 1.8 and 4.4 µm, respectively. Both structural images showed similar features. They also rendered the same retinal vascular network topography. We overlaid OCT angiography with structural B-scans and confirmed their physiological distribution. Besides similarities, the higher resolution of vis-OCT emphasized the fibrous features in the neural fiber layer. It also offered better separation between retinal layers.Blood flow measurements showed comparable results among two subsystems. The total flow rate was 2.71±0.27 and 2.53±0.27 µL/min for arteries and veins in Vis-OCT, respectively. NIR-OCT gave us 2.76±0.17 and 2.52±0.17 µL/min, respectively. No statistical difference was found between the values, further confirming our measurements.We successfully extracted sO2 from vis-OCT. The averaged arterial and venous sO2 was 98±3% and = 85±3%, respectively. However, we failed to extract sO2 from NIR-OCT using the same method. The relative weak absorption and strong scattering did not provide enough contrast to differentiate the two hemoglobin states.
We demonstrated a vis-/NIR dual-band OCT system capable of simultaneous imaging. The two systems have comparable performance in structural imaging, angiography and blood flow measurements. However, vis-OCT has higher resolution and further enables sO2 extraction.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Comparison of Vis- and NIR-OCT. (a, c, e, g) Vis-OCT images. (b, d, f, h) NIR-OCT images.
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