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Jason Dwight, Christina Y. Weng, Michal Pawlowski, Tomasz Tkaczyk; Dye-free angiography of the eye using retinal oximetry. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4659. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Fluorescein angiography (FA) is the gold standard for assessing retinal vasculature; however, its invasive nature can deter its use. The ongoing development of OCT angiography (OCTA) may lead to a non-invasive replacement for FA. Here we present an alternative non-invasive angiography in the form of oxygen abundance extraction from retinal tissue through hyperspectral (HS) imaging. HbO2 values are mapped to intra-vessel and outer-vessel regions to produce an angiographic utility. Its advantage over FA is its dye-free functionality. Its advantage over OCTA is its ability to visualize stagnant blood pooling in the absence of motion contrast.
Using the Image Mapping Spectrometer (IMS), we require no scanning to collect a datacube of 350x350 spatial values and 43 spectral channels (x,y,λ) over 470-670 nm. On a pixel-by-pixel basis, all HS spectra acquired are decomposed using a blind source separation technique to extract HbO2 absorbance spectra (Figure 1). A patient cohort was imaged with the IMS and validated with FA and OCTA. HS data was collected for all 21 eyes of which FA and OCTA were performed for 19 and 6 eyes, respectively. Four eyes are featured here.
We compared HbO2 maps to FA frames (arterial, venous, and late-phase) for eyes with exudative age-related macular degeneration (ARMD), proliferative diabetic retinopathy (PDR), and retinal vein occlusion (RVO). In the eye with ARMD, we observed hyperfluorescence and increased HbO2 (outlined in red) in areas that appear to correspond with drusen. In the eye with RVO, leakage of the disk correlates with increased HbO2 signal (red circle). In the eye with PDR, hyperfluorescence from microvascular leakage is observed in the nasal macula and correlates with increased HbO2 signal (outlined in red). Additionally, laser photocoagulation scars (red arrows) were hypofluorescent on FA with absent HbO2 signal as expected.
Venous-phase FA and HbO2 maps generally exhibit good agreement whereas OCTA and FA findings do not always seem to correlate. We were able to spatially co-locate increased HbO2 signal with regions of FA hyperfluorescence in this study. While our current hardware lacks high spatial sampling and depth-resolved data, future systems can provide these improvements with the integration of higher quality detectors and structured illumination. This preliminary dataset supports IMS as a promising non-invasive alternative to conventional FA.
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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