Eye Clinic, Department of Biomedical and Clinical Science "Luigi Sacco," Sacco Hospital, University of Milan, Milan, Italy; Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, CA.
Doheny Image Reading Center, Doheny Eye Institute, Los Angeles, CA; Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, CA.
Can J Ophthalmol. 2020 Aug;55(4):317-322. doi: 10.1016/j.jcjo.2020.03.011. Epub 2020 May 18.
A variety of binarization strategies have been used to measure vessel density by optical coherence tomography angiography (OCT-A), but it is uncertain if they produce similar results. The purpose of the study was to evaluate the impact of different thresholding methods and contrast and brightness adjustment on OCT-A vessel density metrics.
Observational, cross-sectional case series.
Consecutive healthy volunteers.
Healthy volunteers underwent fovea-centred 3 mm × 3 mm OCT-A scans using PlexElite 9000. Images of the superficial vascular plexus were generated using the instrument's automated segmentation. Images were thresholded with 5 different threshold tools in ImageJ (Default, Huang, IsoDat, Mean, and Otsu), and the threshold grey level value defined by each method was recorded. Brightness and contrast were also increased or decreased by 50% compared with the default. Binarization was performed using the threshold values from each method, and vessel densities were computed and compared.
Superficial plexus vessel density was measured and compared using different adjust threshold tools and changing brightness and contrast.
Twenty eyes of 20 healthy participants were included. Different threshold strategies produced measurements with different mean values (p < 0.0001). Pairwise comparisons revealed differences between all groups (p < 0.0001) except between the IsoData and Otsu thresholding approaches (p > 0.270). Increasing or decreasing the brightness or to 50% of the mean value also yielded statistically significant differences (p < 0.0001).
The method of thresholding and adjustments in contrast and brightness can significantly impact retinal vessel density measurements. These findings highlight the importance of using consistent thresholding strategies for clinical studies.
通过光相干断层扫描血管造影术（OCT-A）测量血管密度的方法有多种，但是否会产生相似的结果尚不确定。本研究旨在评估不同阈值方法和对比度、亮度调整对 OCT-A 血管密度指标的影响。
观察性、横断面病例系列研究。
连续的健康志愿者。
健康志愿者接受基于 PlexElite 9000 的黄斑中心凹 3mm×3mm OCT-A 扫描。使用仪器的自动分割生成浅层血管丛图像。在 ImageJ 中使用 5 种不同的阈值工具（默认值、Huang、IsoDat、Mean 和 Otsu）对图像进行阈值化，并记录每种方法定义的阈值灰度值。与默认值相比，亮度和对比度分别增加或减少 50%。使用每种方法的阈值进行二值化，并计算和比较血管密度。
使用不同的调整阈值工具和改变亮度、对比度，测量并比较浅层血管丛血管密度。
20 名健康志愿者的 20 只眼纳入研究。不同的阈值策略产生的测量值平均值有差异（p<0.0001）。两两比较显示所有组之间均有差异（p<0.0001），但 IsoData 和 Otsu 阈值方法除外（p>0.270）。亮度增加或减少 50%也会产生统计学上的显著差异（p<0.0001）。
阈值方法和对比度、亮度调整会显著影响视网膜血管密度测量值。这些发现强调了在临床研究中使用一致的阈值策略的重要性。
