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David Andrew Miller, Marta Grannonico, Mingna Liu, Xiaorong Liu, Hao Zhang; Enhancing visible-light optical coherence tomography image quality for mouse retinal nerve fiber analysis. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2523.
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© ARVO (1962-2015); The Authors (2016-present)
Our recent studies on visible-light optical coherence tomography (vis-OCT) make it possible to assess optic neuropathy progression in vivo based on retinal ganglion cell (RGC) axon bundle size. However, accurate quantification of these structures by vis-OCT is complicated by speckle noise. We thus implemented two techniques, temporal speckle averaging (TSA) and a novel resampling technique, to improve the visualization of RGC axon bundles in fibergrams and B-scans.
TSA images were acquired from an anesthetized C57BL/6 mouse using vis-OCT. We positioned the optic nerve head (ONH) in one corner of the field of view (FOV) and acquired 5 OCTA volumes consisting of 512 A-lines×512 B-scans with each B-scan repeated 5 times. We repeated this acquisition process with the ONH in each corner of the FOV. A single OCTA volume produced a fibergram, averaged five times, and an unaveraged angiogram. All fibergrams and angiograms at each location were registered and averaged using non-rigid demon registration. Speckle reduced circular scans were reconstructed from 4 rectangular OCT volumes acquired with the ONH positioned in each corner of the FOV. For each volume, an 11 pixel-thick (~15 μm) ring with a 400 μm radius centered on the ONH was plotted. A-lines located along the ring were sorted as a function of angle and averaged within 0.1° sectors to produce a speckle reduced B-scan (SRB-scan).
Fig. 1a shows a montaged fibergram after TSA. Compared to before (Figs. 1b-c), the fibergram and angiogram after TSA (Figs. 1d-e) show smoother structures with greater contrast. RGC axon bundle contrast to noise ratio (CNR) increased 1.5 dB after TSA. Compared to the traditional scan (Fig. 2(a)), individual RGC axon bundles are visible in the SRB-scan (Fig. 2(b)). RGC axon bundle CNR increased 2.4 dB using our novel resampling method.
The combined TSA and resampling greatly enahanced visualization of RGC axon bundles in fibergram and B-scan images, enabling more accurate bundle size analysis.
This is a 2021 ARVO Annual Meeting abstract.
Fig. 1. (a) Montaged speckle reduced fibergram (green) overlaid with angiogram (red). (b-c) Example fibergram and angiogram, respectively, before TSA. (d-e) Fibergram and angiogram, respectively, after TSA.
Fig. 2. (a) Traditional circumpapillary B-scan image (averaged 10 times). (b) Circumpapillary SRB-scan reconstructed from 4 rectangular OCT volumes.
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