The impact of the image conversion factor and image centration on retinal vessel geometric characteristics

Carolin Schanner; Nina Hautala; Franziska G Rauscher; Aura Falck

doi:10.3389/fmed.2023.1112652

The impact of the image conversion factor and image centration on retinal vessel geometric characteristics

Front Med (Lausanne). 2023 Mar 17:10:1112652. doi: 10.3389/fmed.2023.1112652. eCollection 2023.

Authors

Carolin Schanner^{1

2

3}, Nina Hautala^{1

2}, Franziska G Rauscher³, Aura Falck^{1

2}

Affiliations

¹ Department of Ophthalmology and Medical Research Center, Oulu University Hospital, Oulu, Finland.
² PEDEGO Research Unit, University of Oulu, Oulu, Finland.
³ Institute for Medical Informatics, Statistics, and Epidemiology, Leipzig University, Leipzig, Germany.

Abstract

Background: This study aims to use fundus image material from a long-term retinopathy follow-up study to identify problems created by changing imaging modalities or imaging settings (e.g., image centering, resolution, viewing angle, illumination wavelength). Investigating the relationship of image conversion factor and imaging centering on retinal vessel geometric characteristics (RVGC), offers solutions for longitudinal retinal vessel analysis for data obtained in clinical routine.

Methods: Retinal vessel geometric characteristics were analyzed in scanned fundus photographs with Singapore-I-Vessel-Assessment using a constant image conversion factor (ICF) and an individual ICF, applying them to macula centered (MC) and optic disk centered (ODC) images. The ICF is used to convert pixel measurements into μm for vessel diameter measurements and to establish the size of the measuring zone. Calculating a constant ICF, the width of all analyzed optic disks is included, and it is used for all images of a cohort. An individual ICF, in turn, uses the optic disk diameter of the eye analyzed. To investigate agreement, Bland-Altman mean difference was calculated between ODC images analyzed with individual and constant ICF and between MC and ODC images.

Results: With constant ICF (n = 104 eyes of 52 patients) the mean central retinal equivalent was 160.9 ± 17.08 μm for arteries (CRAE) and 208.7 ± 14.7.4 μm for veins (CRVE). The individual ICFs resulted in a mean CRAE of 163.3 ± 15.6 μm and a mean CRVE of 219.0 ± 22.3 μm. On Bland-Altman analysis, the individual ICF RVGC are more positive, resulting in a positive mean difference for most investigated parameters. Arteriovenous ratio (p = 0.86), simple tortuosity (p = 0.08), and fractal dimension (p = 0.80) agreed well between MC and ODC images, while the vessel diameters were significantly smaller in MC images (p < 0.002).

Conclusion: Scanned images can be analyzed using vessel assessment software. Investigations of individual ICF versus constant ICF point out the asset of utilizing an individual ICF. Image settings (ODC vs. MC) were shown to have good agreement.

Keywords: diabetic retinopathy; ophthalmology; retina; retinal image analysis; retinal microvasculature; retinal vessel geometric characteristics (RVGC); retinal vessel parameter.

Grants and funding

CS was supported by Center for International Mobility and Oulu University Scholarship Foundation Fund of Helvi Hakulinen-Sipilä and Eino Sipilä. AF was supported by Duodecim Oulu grant from the Oulu Duodecim Society (https://oulunduodecimseura.yhdistysavain.fi/) and by a grant from Evald and Hilda Nissi Foundation. FGR was supported by a grant from the German Research Foundation (grant number: DFG 497989466). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.