Assessment of Retinal Hemodynamics using Video Fluorescein Angiography Images

Abstract

Purpose : Fluorescein angiography (FA) is a routinely used technique where abnormal fluorescein patterns are qualitatively assessed for the diagnosis of retinal diseases. Quantitative assessment of FA usually faces challenges in variation of acquisition conditions and changes in field of view. We describe a reliable quantitative method to analyses video FA to estimate the retina blood flow (RBF), mean transition time (MTT) and the permeability in the retinal tissues in animal models to assist drug discovery programs.

Methods : Nine spontaneously dysmetabolic non-human primates (NHP) underwent monthly intravitreal administration anti-VEGF (ranibizumab) for 3 months and 6 Dutch belted rabbits with VEGF-induced retinal leakage for 3 days were used in this study. FA video were taken at baseline and post-treatment. Images were acquired at a high temporal resolution during first 1 min at 1~10 frames/sec, followed by acquisition at 1~3 frames/min for up to 10 min.. Images were registrated to achieve pixel-based spatiotemporal analysis. Major arteries and veins were then classified using the differences in fluorescein arrival time. Sudden changes of intensity due to gain change were corrected using a linear model. The videos were then divided into 3 time periods for the quantitative analysis. First period (0~30 sec.) is from the injection of fluorescein dye till re-circulation. RBF and the MTT were calculated using images from this period. Second period (30~60 sec.) and third period (1~10 min) were used to calculate the permeability. Permeability was assessed for each pixel by computing the slope of intensity curve normalized to arterial values. Finally, parametric maps of MTT, RBF and permeability were generated.

Results : The temporal profiles of the fluorescein signal was used to generate the MTT, RBF and permeability maps of the retina. These parametric maps delineated regions of high and low permeability. High permeability regions were observed to be co-localized with regions of hyperfluorescent. Additional hyperpermeable foci were also observed that could not be easily identified from the conventional FA images.

Conclusions : The proposed method for the analysis of video FA images affords an objective and sensitive assessment of retinal hemodynamics and permeability of both NHP and rabbit animal models.

This is a 2020 Imaging in the Eye Conference abstract.

 

MTT, RBF and permeability maps of rabbit eyes showed that the VEGF induced leakage 3 days post treatment.