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. Author manuscript; available in PMC: 2019 Mar 7.
Published in final edited form as: Prog Retin Eye Res. 2017 Dec 8;64:1–55. doi: 10.1016/j.preteyeres.2017.11.003

Fig. 4.

Fig. 4.

Sigmodal relationship between flow and OCTA signal. Motion contrast algorithms for OCTA typically have a sigmoidal relationship between flow and OCTA signal. Decorrelation signal (vertical axis) versus flow speed (horizontal) is shown for long (top) and short (bottom) interscan times. Current commercial instruments use long interscan times (top) and have good sensitivity to slow flows (slowest detectable flow). However, faster flows (above the fastest distinguishable flow) have a saturated OCTA signal and cannot be differentiated. If faster interscan times are used (bottom), the sensitivity to slow flow is lost, but faster flows are no longer saturated, enabling the detection of flow impairment. OCTA using slow interscan times (3.0 ms) detect large numbers of vessels, but poorly detect differences in faster flow. OCTA using fast interscan times (1.5 ms) do not detect vessels having slower flow speeds, but detect differences in faster flow. Using variable interscan times it is possible to differentiate flow impairment. The scale bars are 500 μm and the images are enlarged from a 6 mm × 6 mm field of view (Modified from Choi, Ophthalmology 2015).