High A-scan rate optical coherence tomography angiography for blood flow speed quantification in the retina

Abstract

Optical coherence tomography angiography (OCTA) offers non-invasive and depth-resolved imaging of the retinal vasculature. While OCTA is widely used to study retinal disease, it traditionally provides limited information about blood flow speed. This thesis introduces a second-generation variable interscan time analysis (VISTA) OCTA, designed to evaluate a quantitative surrogate marker for blood flow speed in the vasculature. At the capillary level, spatially compiled OCTA and a simple temporal autocorrelation model, ρ(τ) = exp(-ατ), are used to evaluate a temporal autocorrelation decay constant, α, as a marker for blood flow speed. A 600 kHz A-scan rate swept-source OCT prototype instrument provides short interscan time OCTA and fine A-scan spacing acquisition, while maintaining multi mm2 field-of-views for human retinal imaging. The cardiac pulsatility in α is demonstrated and its synchronization across retinal capillaries is quantified. The repeatability of α measurements is evaluated at multiple spatial levels. This new approach reveals varying α values across different retinal capillary plexuses in healthy eyes, and demonstrates spatial correspondence between high blood flow speeds and the centers of choriocapillaris lobules. VISTA OCTA images of eyes with diabetic retinopathy and age-related macular degeneration are also presented. By providing blood flow speed information, the second-generation VISTA aims to enhance and complement traditional structural vasculature imaging offered by OCTA. These advancements promise to enable clinical studies of blood flow speed alterations in retinal diseases, offering earlier markers for disease detection, progression, and response to treatment.