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Zhang Miao, Thomas S Hwang, J. Peter Campbell, Steven T Bailey, David J Wilson, David Huang, Yali Jia; Projection-Resolved Optical Coherence Tomographic Angiography. Invest. Ophthalmol. Vis. Sci. 2016;57(12):450. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To describe a novel method to remove shadowgraphic projection artifacts in optical coherence tomography angiography (OCT-A)
3x3 mm OCT-A were obtained with a 70 kHz commercial OCT (RTVue-XR) and the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. A novel projection-resolved (PR) resolves the ambiguity between in-situ flow and projected flow by comparing the decorrelation value of each voxel to all shallower voxels within the same axial scan. Slab subtraction (SS), a common method to suppress projection, is used for comparison.
One eye each of 13 healthy human participants (age 25 to 58 years) were scanned in the macula. The average PR results in the parafoveal region show 3 peaks of vessel density that corresponds to the superficial (nerve fiber and ganglion cell layers), intermediate (between inner plexiform and inner nuclear layers [INL]), and deep (between INL and outer plexiform layer [OPL]) plexuses. These vessel density peaks could not be identified on the OCT angiogram without projection suppression or with SS suppression. In OCT-A without projection suppression, deeper slabs are dominated by projection artifacts from the superficial slab. SS suppression removed most projection artifacts from the deeper slabs, but fragmented the capillary network in the intermediate and deep plexuses. PR OCT-A successfully removed projection artifacts while preserving vascular network continuity in the deeper plexuses. PR OCT-A is the only algorithm able to produce truly depth-resolved cross-sectional angiograms with discrete vessels without long tails.
PR OCT-A effectively suppresses the projection artifact while preserving vascular detail in deeper layers. This novel technique is able to, for the first time, resolve 3 distinct retinal vascular plexuses of the human eye non-invasively in vivo. The location of the 3 plexuses agree with previous histology results.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Fig. 1. Cross-sectional angiograms (Row A) and en face superficial plexus (Row B), intermediate plexus (Row C), deep plexus (Row D), and outer retinal slab (Row E) angiograms of unprocessed (Column 1), slab-subtracted (SS, Column 2), and projection-resolved (PR, Column 3) OCT-A.
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