Visualization of Radial Peripapillary Capillaries Using Optical Coherence Tomography Angiography: The Effect of Image Averaging

Abstract

ObjectivesTo assess the effect of image registration and averaging on the visualization and quantification of the radial peripapillary capillary (RPC) network on optical coherence tomography angiography (OCTA).MethodsTwenty-two healthy controls were imaged with a commercial OCTA system (AngioVue, Optovue, Inc.). Ten 10x10° scans of the optic disc were obtained, and the most superficial layer (50-μm slab extending from the inner limiting membrane) was extracted for analysis. Rigid registration was achieved using ImageJ, and averaging of each 2 to 10 frames was performed in five ~2x2° regions of interest (ROI) located 1° from the optic disc margin. The ROI were automatically skeletonized. Signal-to-noise ratio (SNR), number of endpoints and mean capillary length from the skeleton, capillary density, and mean intercapillary distance (ICD) were measured for the reference and each averaged ROI. Repeated measures analysis of variance was used to assess statistical significance. Three patients with primary open angle glaucoma were also imaged to compare RPC density to controls.ResultsQualitatively, vessels appeared smoother and closer to histologic descriptions with increasing number of averaged frames. Quantitatively, number of endpoints decreased by 51%, and SNR, mean capillary length, capillary density, and ICD increased by 44%, 91%, 11%, and 4.5% from single frame to 10-frame averaged, respectively. The 10-frame averaged images from the glaucomatous eyes revealed decreased density correlating to visual field defects and retinal nerve fiber layer thinning.ConclusionsOCTA image registration and averaging is a viable and accessible method to enhance the visualization of RPCs, with significant improvements in image quality and RPC quantitative parameters. With this technique, we will be able to non-invasively and reliably study RPC involvement in diseases such as glaucoma.

Multiple enface image averaging for enhanced optical coherence tomography angiography imaging

“…Multiple B-scan averaging technique is a commonly used method to decrease speckle noise and enhance SD-OCT image quality improving visualization of the fine structures in OCT B-scan (Sander et al 2005;Jorgensen et al 2007;Sakamoto et al 2008;Pappuru et al 2012). Our group and others have shown that averaging can also be applied to enface OCTA images (Maloca et al 2017;Mo et al 2017;Uji et al 2017) and can have an impact on quantitative OCTA metrics. In this study, we evaluate the impact of averaging on image quality, both subjectively and objectively, and propose a level of averaging for optimal image quality.…”

“…Even in images with minimum artefact, background noise or small discontinuities in the microcirculation are common. Our group and others have shown that averaging can also be applied to enface OCTA images (Maloca et al 2017;Mo et al 2017;Uji et al 2017) and can have an impact on quantitative OCTA metrics. lower resolution) OCTA images, whether the discontinuity of the vessels is further accentuated due to decrease in decorrelation signals per unit area is obvious.…”

Microvasculature dropout detected by the optical coherence tomography angiography in nonarteritic anterior ischemic optic neuropathy

“…It has the ability to show both structural and blood flow information. Split‐spectrum amplitude‐decorrelation angiography (SSADA) algorithm (a vital component of OCTA software) helps to quantified the ONH perfusion and retinal vasculature . Published studies describe potential efficacy for OCTA in the evaluation of some ocular diseases such as NAION, glaucoma, multiple sclerosis, diabetic retinopathy, age related macular degeneration (AMD), and so on .…”

Optical coherence tomography angiography of the peripapillary capillaries in primary open-angle and normal-tension glaucoma

“…Although glaucoma has been investigated intensely over the years, the elucidation of blood flow and microvasculature in the optic discs of patients with glaucoma remains a challenging research topic. Previous studies of glaucoma often reported fluorescein angiography findings of filling defects (no contrast enhancement) in the intrapapillary capillaries and the disappearance of radial peripapillary capillaries (RPCs) accompanied by an RNFL defect, generating discussions about whether these defects precede or follow visual field loss [ 7 , 8 ]. In addition, reduced intrapapillary, peripapillary, and macular blood flow was recently reported in patients with glaucoma, based mostly on laser speckle flowgraphy (LSFG) findings [ 9 , 10 ].…”