Optical coherence tomography angiography uses motion contrast to detect flow from the optical coherence tomography (OCT) data; thus, flow is defined as the difference in signal between 2 sequential B-scans. Stationary tissue will show no variation between consecutive B-scans; however, blood flow will result in disparities between B-scans, resulting in a map of blood flow that appears as red pixels on the structural B-scan. A 3-dimensional (3D) angiogram is then created via evaluation of multiple motion contrast B-scans. Tandem viewing of OCT angiograms and B-scans allows for rapid identification and interpretation of retinal and choroidal pathologies (Figures 1-1 through 1-3).
Figure 1-1. Rapid acquisition of 2 sequential B-scans.
Figure 1-2. B-scan with flow overlay. Red pixelation represents blood flow within retina and choroid.
Figure 1-3. Angiogram.
En face angiograms are created by analyzing the flow information within the selected anatomic layer on the B-scan. Analyzing the en face images (OCT angiograms) provides blood flow information at different depths of the retina and choroid (Figure 1-4).
Figure 1-4. (A) Superficial capillary plexus: Internal limiting membrane to inner plexiform layer. (B) Deep capillary plexus : Inner plexiform layer to outer plexiform layer (OPL). (C) Outer retina: OPL to Bruch’s membrane. (D) Choriocapillaris.
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