Impact of Binarization Thresholding and Brightness/Contrast Adjustment Methodology on Optical Coherence Tomography Angiography Image Quantification

• Published in: American journal of ophthalmology 2019-09, Vol.205, p.54-65
• Main Authors: Mehta, Nihaal, Liu, Keke, Alibhai, A. Yasin, Gendelman, Isaac, Braun, Phillip X., Ishibazawa, Akihiro, Sorour, Osama, Duker, Jay S., Waheed, Nadia K.
• Format: Article
• Language: English
• Subjects: Cross-Sectional Studies; Female; Fluorescein Angiography - methods; Fundus Oculi; Healthy Volunteers; Humans; Image Enhancement; Male; Medical imaging; Prospective Studies; Reproducibility of Results; Retinal Vessels - diagnostic imaging; Software; Tomography; Tomography, Optical Coherence - methods
• ISSN: 0002-9394; 1879-1891
• DOI: 10.1016/j.ajo.2019.03.008

Binarization is a critical technique in optical coherence tomography angiography (OCTA) image analysis, but there is no consistency in the method used in published OCTA studies. This study assessed whether differences in OCTA binarization and brightness and contrast adjustments affect quantification measurements. Prospective cross-sectional validity study. This was a single-center study examining 21 eyes of 11 healthy individuals. All eyes were imaged using a swept-source OCTA (Zeiss), and quantitative measurements resulting from five binarization thresholding and five brightness/contrast adjustment methods were compared. All measurements were calculated for the superficial plexus and choriocapillaris (CC), as well as unaveraged and averaged en face OCTA images. There were statistically significant differences between measurements from different binarization thresholding methods (P < 0.0001), as well as measurements from different histogram adjustments (P < 0.0001). The binarization thresholds yielded different measurements when combined with variable brightness/contrast adjustments. The method of analysis also affected the directionality of trends in imaging measurements between unaveraged and averaged CC images. The method of OCTA image binarization thresholding and histogram adjustment significantly alters quantitative measurements and the directionality of trends. Results obtained from different OCTA binarization methods should be seen as valid only for that given method. This has significant consequences for clinical trials using OCTA measurements as outcome measurements. A consensus is needed across the research community for a consistent method for OCTA image quantification and greater attention paid to fully describing methods in published studies.