University of Oulu

Schanner C, Hautala N, Rauscher FG and Falck A (2023) The impact of the image conversion factor and image centration on retinal vessel geometric characteristics. Front. Med. 10:1112652. doi: 10.3389/fmed.2023.1112652

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

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Author: Schanner, Carolin1,2,3; Hautala, Nina1,2; Rauscher, Franziska G.3;
Organizations: 1Department of Ophthalmology and Medical Research Center, Oulu University Hospital, Oulu, Finland
2PEDEGO Research Unit, University of Oulu, Oulu, Finland
3Institute for Medical Informatics, Statistics, and Epidemiology, Leipzig University, Leipzig, Germany
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.8 MB)
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Language: English
Published: Frontiers Media, 2023
Publish Date: 2023-08-11


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.

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Series: Frontiers in medicine
ISSN: 2296-858X
ISSN-E: 2296-858X
ISSN-L: 2296-858X
Volume: 10
Article number: 1112652
DOI: 10.3389/fmed.2023.1112652
Type of Publication: A1 Journal article – refereed
Field of Science: 3121 General medicine, internal medicine and other clinical medicine
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 ( 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.
Copyright information: © 2023 Schanner, Hautala, Rauscher and Falck. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.