Department of Ophthalmology, IRCCS San Raffaele Scientific Institute, Vita-Salute University, via Olgettina 60, 20132, Milan, Italy.
Sci Rep. 2021 Jul 20;11(1):14758. doi: 10.1038/s41598-021-94333-y.
Optical coherence tomography angiography (OCTA) provides several data regarding the status of retinal capillaries. This information can be further enlarged by employing quantitative metrics, such as vessel density (VD). A mandatory preliminary step of OCTA quantification is image binarization, a procedure used to highlight retinal capillaries on empty background. Although several binarization thresholds exist, no consensus is reached about the thresholding technique to be used. In this study, we tested thirteen binarization thresholds on a dataset made by thirty volunteers. The aim was to assess the impact of binarization techniques on: (I) detection of retinal capillaries, assessed by the calculation of overlapping percentages between binarized and original images; (II) quantitative OCTA metrics, including VD, vessel tortuosity (VT) and vessel dispersion (Vdisp); (III) foveal avascular zone (FAZ) detection. Our findings showed Huang, Li, Mean and Percentile as highly reliable binarization thresholds (p < 0.05), whereas the worst binarization thresholds were Intermodes, MaxEntropy, RenylEntropy and Yen (p < 0.05). All the thresholds variably underestimated VD metric and FAZ detection, with respect to the original OCTA images, whereas VT and Vdisp turned out to be more stable. The usage of a Fixed threshold resulted extremely useful to reduce VD and FAZ underestimations, although bound to operators' experience.
光学相干断层扫描血管造影术（OCTA）提供了有关视网膜毛细血管状态的多项数据。通过使用定量指标（如血管密度（VD））可以进一步扩大这些信息。OCTA 量化的强制性初步步骤是图像二值化，该过程用于突出显示空白背景上的视网膜毛细血管。尽管存在几种二值化阈值，但尚未就要使用的阈值技术达成共识。在这项研究中，我们在由三十名志愿者组成的数据集上测试了十三个二值化阈值。目的是评估二值化技术对以下方面的影响：（I）视网膜毛细血管的检测，通过计算二值化图像和原始图像之间的重叠百分比来评估；（II）定量 OCTA 指标，包括 VD、血管迂曲度（VT）和血管离散度（Vdisp）；（III）中心凹无血管区（FAZ）检测。我们的研究结果表明，Huang、Li、Mean 和 Percentile 是高度可靠的二值化阈值（p<0.05），而最差的二值化阈值是 Intermodes、MaxEntropy、RenylEntropy 和 Yen（p<0.05）。所有阈值都不同程度地低估了 VD 指标和 FAZ 检测，与原始 OCTA 图像相比，而 VT 和 Vdisp 则更为稳定。使用固定阈值可以极大地减少 VD 和 FAZ 的低估，尽管这取决于操作员的经验。
