Garg Itika, Miller John B
Retina Service, Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA.
Harvard Retinal Imaging Lab, Boston, MA, USA.
Quant Imaging Med Surg. 2023 Jun 1;13(6):3688-3702. doi: 10.21037/qims-21-1175. Epub 2023 Mar 20.
The clinical application of optical coherence tomography angiography (OCTA) has been well documented in literature with its promising potential in dye-less evaluation of various retinal vascular pathologies. Recent advances in OCTA help us gather wider field of view with 12 mm × 12 mm and montage compared to the standard dye-based scans, which has a higher accuracy and sensitivity in detection of peripheral pathologies. The aim of this study is to build a semi-automated algorithm to precisely quantify the non-perfusion areas (NPAs) on widefield swept-source optical coherence tomography angiography (WF SS-OCTA).
All subjects underwent imaging on 100 kHz SS-OCTA device acquiring 12 mm × 12 mm angiograms centered on fovea and optic disc. After a comprehensive literature review, a novel algorithm using FIJI (ImageJ) was designed to calculate the NPAs (mm) after excluding the threshold and segmentation artifact areas from the total field of view. Segmentation and threshold artifacts were first removed from enface structure images using the spatial variance and mean filter respectively. Vessel enhancement was achieved by using 'Subtract Background' followed by directional filter. The cut off for Huang's fuzzy black and white thresholding was defined from the pixel values based of the foveal avascular zone. Then, the NPAs were calculated using the 'Analyze Particles' command with a minimum size of ~0.15 mm. Finally, the artifact area was subtracted from to give the corrected NPAs.
Our cohort had 44 eyes of 30 control patients and 107 eyes of 73 patients with diabetes mellitus (both median age 55 years, P=0.89). Of 107 eyes, 21 eyes had no evidence of diabetic retinopathy (DR), 50 eyes had non-proliferative DR and 36 eyes had proliferative DR. The median NPA was 0.20 (0.07-0.40) in controls, 0.28 (0.12-0.72) in no DR, 5.54 (3.12-9.10) in non-proliferative DR and 13.38 (8.73-26.32) in proliferative DR eyes. Using mixed effects-multiple linear regression analysis adjusting for age, there was significant progressive increase in NPA with increasing DR severity.
This is one of the first study to use the directional filter for WFSS-OCTA image processing which is known to be superior to other Hessian based multiscale, linear, and non-linear filters especially for vascular analysis. Our method could greatly refine and streamline the calculation of signal void area proportion, while being much quicker and accurate than manual delineation of NPAs and subsequent estimation. This combined with the wide field of view can have a great prognostic and diagnostic clinical impact for future applications in DR and other ischemic retinal pathologies.
光学相干断层扫描血管造影（OCTA）的临床应用在文献中已有充分记载，其在无染料评估各种视网膜血管病变方面具有广阔前景。与标准的基于染料的扫描相比，OCTA的最新进展使我们能够获得12毫米×12毫米的更宽视野和拼接图像，在检测周边病变方面具有更高的准确性和敏感性。本研究的目的是建立一种半自动算法，以精确量化广角扫频源光学相干断层扫描血管造影（WF SS-OCTA）上的无灌注区（NPA）。
所有受试者均在100kHz SS-OCTA设备上进行成像，获取以黄斑和视盘为中心的12毫米×12毫米血管造影图像。在全面的文献综述之后，设计了一种使用FIJI（ImageJ）的新型算法，在从总视野中排除阈值和分割伪影区域后计算NPA（平方毫米）。首先分别使用空间方差和均值滤波器从正面结构图像中去除分割和阈值伪影。通过使用“减去背景”然后进行方向滤波来实现血管增强。基于黄斑无血管区的像素值定义了黄氏模糊黑白阈值的截止值。然后，使用“分析粒子”命令计算NPA，最小尺寸约为0.15平方毫米。最后，从其中减去伪影区域以得到校正后的NPA。
我们的队列包括30名对照患者的44只眼和73名糖尿病患者的107只眼（中位年龄均为55岁，P = 0.89）。在107只眼中，21只眼没有糖尿病视网膜病变（DR）的证据，50只眼有非增殖性DR，36只眼有增殖性DR。对照组的中位NPA为0.20（0.07 - 0.40），无DR组为0.28（0.12 - 0.72），非增殖性DR组为5.54（3.12 - 9.10），增殖性DR组为13.38（8.73 - 26.32）。使用调整年龄后的混合效应多元线性回归分析，随着DR严重程度的增加，NPA有显著的逐渐增加。
这是首批使用方向滤波器进行WFSS-OCTA图像处理的研究之一，已知该滤波器优于其他基于黑森矩阵的多尺度、线性和非线性滤波器，特别是在血管分析方面。我们的方法可以极大地优化和简化信号空洞面积比例的计算，同时比手动描绘NPA和后续估计更快、更准确。这与宽视野相结合，对于未来在DR和其他缺血性视网膜病变中的应用可能具有重大的预后和诊断临床影响。
