Image Analysis of Optical Coherence Tomography Angiography.

Optical coherence tomography (OCT) angiography (OCT-A) is a transformative approach in imaging ocular vessels based on flow rather than simple reflectance intensity. It is therefore a functional extension of OCT that can be used to visualize microvasculature by detecting motion contrast from flowing blood. As OCT-A is a depth-resolved examination, it needs careful axial segmentation in order to preserve important data on perfused structures and to avoid the risk of generating superimposed images, which are typical of dye angiographies. An automated segmentation algorithm for both retinal and choroidal layers is provided by the majority of different OCT-A devices. In the case of accentuated macular retinal/choroidal disruptions causing potential segmentation errors, specific manual correction allows one to modify the shape and the localization of each layer. In the case of manual segmentation, the thickness of every C-scan may be modified in order to provide a constant thickness of tissue slices at different retinal or choroidal levels. OCT projection artifacts also occur from superficial retinal vessels, which can be seen in deeper retinal layers, or retinal and choroidal vessels, which can even be seen in the scleral tissue. These projection artifacts are almost always present and are visible in any layer that is located below the perfused vasculature.