Laiginhas Rita, Cabral Diogo, Falcão Manuel
Department of Ophthalmology, CHEDV, Portugal.
PDICSS, Faculty of Medicine of the University of Porto, Porto, Portugal.
Quant Imaging Med Surg. 2020 Oct;10(10):1994-2005. doi: 10.21037/qims-20-340.
In this paper, we evaluate the different thresholding strategies that have been used for the quantification of the choriocapillaris (CC) and explore their repeatability and the interchangeability of the measurements resulting from its application.
Observational study. Eighteen eyes from nine healthy volunteers aged >18 years were imaged four consecutive times with a SD-OCTA system (Heidelberg Engineering, Germany) using a 10°×10° high-resolution protocol centered on the fovea. Projection artifacts were removed, and the CC was bracketed between 10 and 30 µm below Bruch's membrane. For the quantification of CC, we used four flow deficits (FD) parameters: FD number, mean FD size, total FD area and FD density. We performed a systematic review of literature to collect the thresholding methods that have been used for the quantification of CC. The CC quantification parameters were then evaluated after applying each of the thresholding strategies. Intraclass correlation coefficient (ICC) and Pearson's correlation analysis were used to compare the repeatability and interchangeability among the different thresholding strategies for quantifying the CC.
A total of 72 optical coherence tomography angiography (OCTA) examinations were considered. The systematic review allowed us to conclude that three local thresholding strategies (Phansalkar, mean and Niblack) and three global thresholding strategies (mean, default, Otsu) have been used for CC quantification. These strategies were evaluated in our observational study. We found a high agreement within the same method in the quantification of FD number, mean FD size, total FD area and FD density but a poor agreement with different strategies. Local strategies achieved a significantly superior ICC than global ones in CC quantification.
In conclusion, the interchangeability of the CC quantification using different thresholding strategies is low, and direct comparisons should not be performed. Local thresholding strategies are significantly superior to global ones for quantifying CC and should be preferred. There is an unmet need for a uniform strategy to quantify CC in future studies.
在本文中，我们评估了用于脉络膜毛细血管（CC）定量分析的不同阈值策略，并探讨了它们的可重复性以及应用这些策略所产生测量结果的互换性。
观察性研究。使用德国海德堡工程公司的谱域光学相干断层扫描血管造影（SD-OCTA）系统，以黄斑为中心采用10°×10°高分辨率方案，对9名年龄大于18岁的健康志愿者的18只眼睛进行连续4次成像。去除投影伪影，将CC定位在布鲁赫膜下方10至30μm之间。为了对CC进行定量分析，我们使用了四个血流缺失（FD）参数：FD数量、平均FD大小、总FD面积和FD密度。我们对文献进行了系统回顾，以收集用于CC定量分析的阈值方法。然后在应用每种阈值策略后评估CC定量参数。使用组内相关系数（ICC）和皮尔逊相关分析来比较不同阈值策略在量化CC时的可重复性和互换性。
共纳入72次光学相干断层扫描血管造影（OCTA）检查。系统回顾使我们得出结论，三种局部阈值策略（Phansalkar、均值和Niblack）和三种全局阈值策略（均值、默认、大津）已用于CC定量分析。这些策略在我们的观察性研究中进行了评估。我们发现在FD数量、平均FD大小、总FD面积和FD密度的定量分析中，同一方法内具有高度一致性，但不同策略之间的一致性较差。在CC定量分析中，局部策略的ICC显著优于全局策略。
总之，使用不同阈值策略进行CC定量分析的互换性较低，不应进行直接比较。在量化CC方面，局部阈值策略显著优于全局策略，应优先选用。未来研究中迫切需要一种统一的策略来量化CC。
