11/4/2023 0 Comments Optical coherence angiographyFlowing red blood cells causes more variation in the OCT signal between repeated scans than static tissue. OCTA identifies blood vessels by detecting the blood flow-induced change in the OCT reflectance signal. In this review article, we discuss the history of OCTA as well as its technical principles and clinical applications. Despite its insensitivity to leakage and the relatively small field of view, the development of OCTA has the potential to improve our knowledge of the physiology and pathophysiology of the eye. OCTA detects the motion of blood using intrinsic signals to capture the location of blood vessels. It has the capability of producing high-resolution, 3D angiograms of the retinal and choroidal vascular networks. OCT angiography (OCTA) is a more recent development. DOCT is sensitive to blood flow parallel to the OCT beam, whereas flow in the retinal microvasculature is mainly perpendicular to the OCT beam. However, DOCT is less suitable for investigating the retinal microvasculature. Doppler OCT (DOCT) uses the Doppler frequency shift resulting from the movement of red blood cells to quantify volumetric blood flow in large vessels, as well as for total retinal blood flow measurement. However, their clinical use has been limited by their complexity, poor reproducibility, and wide population variation.įunctional extensions of OCT have also been explored for vascular imaging of the eye. Other imaging modalities such as laser Doppler flowmetry and velocimetry, blue field entoptic technique, and laser speckle assessment have been used extensively to study vascular retinal physiology. While they were able to provide good tissue penetration, they did not receive much clinical attention in ophthalmology due to poor resolution and measurement reproducibility. Ultrasound color Doppler and functional magnetic resonance imaging have been previously used for research purposes. Multiple noninvasive imaging technologies have been employed in the last few decades to visualize and quantify ocular circulations. Moreover, FA and ICGA provide two-dimensional (2D) images of ocular circulations, limiting depth perception and detailed investigation of the retinal and choroidal vasculatures. They require intravenous injection of contrast agents, which is time-consuming and can have potentially serious side effects. Conventionally, fluorescein angiography (FA) and indocyanine green angiography (ICGA) are used for qualitative clinical assessment of retinal and choroidal circulations, respectively. Given that many ocular diseases are associated with vascular abnormalities, the ability to visualize and quantify blood flow in the eye is of high importance to the global ophthalmic community. However, structural OCT cannot be used to monitor vascular changes because of the low contrast between capillaries and retinal tissue. It generates high-resolution, cross-sectional images from backscattered light, enabling clinicians to assess structural changes in different retinal diseases. OCT is a noninvasive imaging technology based on low-coherence interferometry. Since its invention in the early 1990s, optical coherence tomography (OCT) has become one of the most important imaging modalities in ophthalmology.
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