Schanner Carolin, Hautala Nina, Rauscher Franziska G, Falck Aura
Department of Ophthalmology and Medical Research Center, Oulu University Hospital, Oulu, Finland.
PEDEGO Research Unit, University of Oulu, Oulu, Finland.
Front Med (Lausanne). 2023 Mar 17;10:1112652. doi: 10.3389/fmed.2023.1112652. eCollection 2023.
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.
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.
With constant ICF ( = 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 ( = 0.86), simple tortuosity ( = 0.08), and fractal dimension ( = 0.80) agreed well between MC and ODC images, while the vessel diameters were significantly smaller in MC images ( < 0.002).
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.
本研究旨在利用长期视网膜病变随访研究中的眼底图像资料，识别因成像方式或成像设置改变（如图像居中、分辨率、视角、照明波长）而产生的问题。研究图像转换因子与成像中心对视网膜血管几何特征（RVGC）的关系，为临床常规获取的数据进行纵向视网膜血管分析提供解决方案。
使用新加坡-I-血管评估法，在扫描的眼底照片中分析视网膜血管几何特征，采用恒定图像转换因子（ICF）和个体ICF，并将其应用于黄斑中心（MC）和视盘中心（ODC）图像。ICF用于将像素测量值转换为微米以进行血管直径测量，并确定测量区域的大小。计算恒定ICF时，纳入所有分析视盘的宽度，并将其用于一组人群的所有图像。而个体ICF则使用所分析眼睛的视盘直径。为研究一致性，计算个体ICF和恒定ICF分析的ODC图像之间以及MC和ODC图像之间的Bland-Altman平均差异。
采用恒定ICF（52例患者的104只眼）时，动脉的平均中央视网膜等效值（CRAE）为160.9±17.08μm，静脉的平均中央视网膜等效值（CRVE）为208.7±14.74μm。个体ICF得出的平均CRAE为163.3±15.6μm，平均CRVE为219.0±22.3μm。在Bland-Altman分析中，个体ICF的RVGC更正，导致大多数研究参数的平均差异为正。动静脉比（=0.86）、简单迂曲度（=0.08）和分形维数（=0.80）在MC和ODC图像之间一致性良好，而MC图像中的血管直径明显较小（<0.002）。
扫描图像可使用血管评估软件进行分析。个体ICF与恒定ICF的研究指出了使用个体ICF的优点。图像设置（ODC与MC）显示出良好的一致性。
