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Hao Zhou, Jie Lu, Kelly Chen, Yingying Shi, Giovanni Gregori, Philip J Rosenfeld, Ruikang Wang; Accurate measurement of choroidal vascularity index in eyes with hyper/hypo transmission defects using SS-OCT. Invest. Ophthalmol. Vis. Sci. 2021;62(11):29.
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Choroidal vascularity index (CVI) has been reported to associate with choroid-related pathologies. Because CVI is calculated as volume/area ratio of binarized vessel in choroid, signal intensity alternation due to hyper/hypo-transmission defects (HTD) from drusen, PED, RPE tear or atrophy will affect the thresholding of choroid vessels. Therefore, we developed a simulation model to verify CVI quantification in eyes with HTDs and demonstrated that accurate CVI can be achieved after attenuation correction on SS-OCT 3D datasets.
6×6 mm scans were acquired (PLEX® Elite, Carl Zeiss Meditec Inc) from normal subjects. Signal intensity in a cylindrical region below BM was altered with a hyper/hypo-transmission ratio (HTR) to mimic HTD. Signals below background noises and above saturation level were randomized. CVIs were calculated using the Otsu’s method before and after attenuation correction. Patients with geographic atrophy (GA) or initially had drusen, which later collapsed were recruited. CVI of eyes with GA or drusen were compared with and without attenuation correction.
10 normal eyes were recruited to generate the HTD simulation model and CVI from the original scans were used as “ground truth”. CVIs were overestimated in eyes with hypo-TD and underestimated in eyes with hyper-TD (Fig.1). After attenuation correction, the uneven distribution of signal intensity was eliminated and the resulting CVI showed no significant difference with the ‘ground truth’ (Fig. 2). Attenuation correction successfully eliminated the HTD caused by GA or drusen. No significant difference was found in CVIs of eyes before and after drusen collapse.
The proposed simulation model should be useful in revealing the impact of HTD in CVI quantification, providing a standard to verify CVI methodologies, which are useful to study choroid-involved ocular diseases. CVIs of eyes with GA or drusen demonstrated the importance of attenuation correction to ensure accurate choroidal vessel segmentation.
This is a 2021 Imaging in the Eye Conference abstract.
Fig 1. A simulation model of HTD. Enface sub-RPE slab (A), representing B-scan (B), histogram of signal intensity (C) and enface CVI map (D) from simulated scans with HTR of 0.70, 1.00 and 1.30.
Fig.2. Attenuation correction eliminated choroidal HTD as seen from enface sub-RPE slab (A) and representing B-scan (B), resulting in similar histogram of signal intensity (C) and enface CVI map (D).
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