Elsevier

Ophthalmology

Volume 124, Issue 7, July 2017, Pages 944-952
Ophthalmology

Original article
Impact of Multiple En Face Image Averaging on Quantitative Assessment from Optical Coherence Tomography Angiography Images

https://doi.org/10.1016/j.ophtha.2017.02.006Get rights and content

Purpose

To investigate the impact of multiple en face image averaging on quantitative measurements of the retinal microvasculature using optical coherence tomography angiography (OCTA).

Design

Prospective, observational, cross-sectional case series.

Participants

Twenty-one healthy individuals with normal eyes.

Methods

Macular OCTA images were acquired from all participants using the Zeiss Cirrus 5000 with Angioplex OCTA software (Carl Zeiss Meditec, Dublin, CA). Nine OCTA cube scans per eye were obtained and 9 superficial retinal layer (SRL) and deep retinal layer (DRL) en face OCTA image slabs were averaged individually after registration. Quantitative parameters from the retinal microvasculature were measured on binarized and skeletonized OCTA images and compared with single OCTA images without averaging.

Main Outcome Measures

Vessel density (VD), vessel length density (VLD), vessel diameter index (VDI), and fractal dimension (FD).

Results

Participants with artifact or poor image quality were excluded, leaving 18 eyes for the analysis. After averaging, qualitatively there was apparent reduction in background noise, and fragmented vessels in the images before averaging became continuous with smoother walls and showed sharper contrast in both the SRL and DRL. Binarized and skeletonized derivates of these averaged images also showed fewer line fragments and dots in nonvascular areas and more continuous vessel images than those of images without averaging. In both SRL and DRL, VD (P = 0.0010 and P = 0.0003, respectively), VLD (P < 0.0001 for both), and FD (P < 0.0001 for both) significantly decreased and VDI significantly increased after averaging (P < 0.0001 for both).

Conclusions

Averaging of multiple en face OCTA images improves image quality and also significantly impacts quantitative measurements. Reducing noise that could be misinterpreted as flow and annealing discontinuous vessel segments seem to be major mechanisms by which averaging may be of benefit.

Section snippets

Methods

This was a prospective, observational, cross-sectional case series. This study was approved by the Institutional Review Board of the University of California, Los Angeles, and was conducted in accordance with the tenets of the Declaration of Helsinki and in compliance with the regulations set forth by the Health Insurance Portability and Accountability Act. Written informed consent was obtained from all examined healthy individuals before they participated in the study.

Results

Two eyes with off-center scans and 1 eye with nonuniform illumination in some scans did not meet the prespecified quality criteria and were excluded from the analyses. Thus, 18 eyes from 18 participants were included in the final analysis. These participants had an average age of 34.9±5.9 years (range, 24–49 years). Eight participants were men and 10 were women.

Image quality assessment by masked reading center graders (S.B. and E.B.) revealed that in all cases, the averaged image was rated to

Discussion

In this study, we evaluated the impact of multiple en face image averaging on quantitative parameters commonly derived from OCTA images. Our findings showed a significant difference in quantitative measurements between the original image and averaged images, suggesting that the noise and vessel discontinuities apparent in unaveraged images do have a significant impact on these quantitative parameters. Considering that current OCTA measurements are highly dependent on the result of binarization,

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    Financial Disclosure(s): The author(s) have made the following disclosure(s): S.R.S.: Consultant – Carl Zeiss Meditec, Optos, Allergan, Genentech, Alcon, Novartis, Roche, Regeneron, Bayer, Thrombogenics, Stemm Cells, Inc, Avalanche; Financial support – Carl Zeiss Meditec, Optos, Allergan, Genentech

    Supported by the Astellas Foundation for Research on Metabolic Disorders (A.U.).

    Author Contributions:

    Conception and design: Uji, Sadda

    Analysis and interpretation: Uji, Balasubramanian, Lei, Baghdasaryan, Al-Sheikh, Sadda

    Data collection: Uji, Balasubramanian, Lei, Baghdasaryan, Al-Sheikh

    Obtained funding: none

    Overall responsibility: Uji, Sadda

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