Attenuation correction assisted automated choroidal vessel visualization and quantification in eyes with atrophy

Abstract

Purpose : To develop automated visualization and quantification of choroidal vessels in the entire scanning volume of eyes with geographic atrophy using SS-OCT, with improved attenuation correction to overcome the issues of choroidal hypertransmission.

Methods : Subjects with geographic atrophy (GA) were imaged using a SS-OCT (PLEX® Elite 9000; ZEISS, Dublin, CA; central wavelength: 1050 nm, scanning rate: 100 kHz). 6x6 mm macular scans were obtained and processed by the improved attenuation correction algorithm. Choroid slab was segmented automatically from Bruch’s membrane to the outer boundary of choroidal vessels. Choroidal vessels were further segmented using Otsu’s thresholding method and volumetric choroidal vascularity index (CVI) was calculated. The en face CVI mapping calculates the ratio of vessel pixels to the full depth of choroid in each A-scan. CVIs were compared on eyes under and outside atrophy with and without attenuation correction as well as between GA patients and age-matched normals.

Results : 30 patients with GA were recruited in the study. Histogram of OCT signals demonstrated that choroidal hypertransmission caused uneven illumination of choroid structure under and outside atrophy. This resulted in shadows of atrophy in en face vasculature map when extracting dark lumens that correspond to choroidal vessels, leading to failure of Otsu’s method to segment vessels (Fig 1. A-E). With attenuation correction, we observed identical pixel intensity distributions under and outside atrophy both in B-scans and in 3D choroid slabs. En face choroidal vasculature showed continuous vessels across GA region, meeting the requirement of Otsu’s method to segment choroid vessels (Fig 1. F-J). Statistical analysis showed significantly reduced CVI in eyes with atrophy compared with age-matched normals.

Conclusions : The improved attenuation correction approach can be used to better visualize and quantify choroidal vessels in eyes with atrophy. This technique overcomes the issues with hypertransmittion and provides reliable CVI quantifications. It may be useful to provide better understanding of the role that choroid plays in atrophy-related pathologies.

This is a 2020 ARVO Annual Meeting abstract.

 

Figure 1. Choroidal vessels visualization and quantification with and without attenuation correction.