Purpose
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A tool for grading micro-aneurysms and the Foveal Avascular Zone (FAZ) in Fluorescein Angiography (FA) and OCT Angiography (OCTA) has been developed. With this tool the user can compare visibility and grade micro-aneurysms by displaying early FA, late FA and inner, intermediate and outer OCTA images in a synchronized view.
Methods
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The user can register the images in two steps by clicking on corresponding landmarks: early and late FA should be registered, as well as early FA to OCTA. A least-squares approximation to the affine transform that best matches the annotated point sets is calculated. Visual feedback is available during this stage by blending the images that need to be registered.
Once the images are registered, a synchronized cursor helps the user in finding and comparing micro-aneurysms in all five images. The FAZ, for which the area is automatically calculated, can be drawn onto each image as well.
Results
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Early and late FA and OCTA images, segmented into an inner, intermediate and outer layer, have been acquired for 31 eyes of 24 patients with Diabetic Macular Edema (DME). In every set of images, enough landmarks could be found for successful registration. The affine transform was sufficiently accurate to compare micro-aneurysms in the different images. The tool has been used for grading visibility and leakage of 567 micro-aneurysms. The FAZ could be delineated accurately in each image except the late FA where it was not visible.
Conclusion
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We developed a tool that can help researchers in comparing properties of FA and OCTA images, by registration of 5 different images (early and late FA, inner, intermediate and outer OCTA). The tool has been used for grading micro-aneurysms and delineating the FAZ for patients with DME.