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Charles A Reisman, Zhenguo Wang, Jonathan Jaoshin Liu, Qi Yang, Ying Dong, Kinpui Chan; Swept source OCT angiography based on ratio analysis. Invest. Ophthalmol. Vis. Sci. 2016;57(12):452. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To demonstrate an innovative OCT angiography method with improved detection sensitivity of low blood flow and reduced motion artifacts without compromising axial resolution using commercially available swept source OCT (SS-OCT).
We performed SS-OCT imaging (DRI OCT-1, Topcon, Tokyo, Japan) at 100,000 A-scans per second in both healthy and diseased eyes. Volumetric OCT scans were acquired with real-time tracking using infrared fundus images. OCT angiography scans were typically acquired over a 3mm x 3mm field of view on the retina and consisted of up to 320 A-scans x 320 B-scan positions where each B-scan position was repeatedly scanned 4 times.For SS-OCT angiography processing, our newly developed OCT Angiography Ratio Analysis (OCTARA) was performed. B-scan repetitions at each scan location were registered. The one-sided ratio analysis was computed between corresponding image pixels as defined in Fig. 1, where I(x, y) is the OCT signal intensity, N is the number of scanned B-scan combinations at the given location, and i and j represent the two frames within any given combination of frames. Motion artifacts were suppressed by active tracking during scan acquisition and by selectively averaging over multiple B-scan combinations.
The ratio analysis is a relative measurement of OCT signal amplitude change and enhances the minimum detectable signal compared to other techniques based on variance and decorrelation measurements. Our OCTARA method preserves the integrity of the entire spectrum and therefore does not suffer from compromised axial resolution, an inherent disadvantage of split-spectrum OCT angiography techniques. Using OCTARA, vascular structure is more uniformly visualized with better detection sensitivity of low flow compared to intensity differentiation-based optical microangiography (OMAG). The vascular network is also better visualized compared to split-spectrum amplitude-decorrelation angiography (SSADA) where differences in relative angiographic signal intensity are due both to the separate factors of full-spectrum versus split-spectrum and of ratio versus amplitude decorrelation calculations.
Our innovative OCT angiography processing method, based on a ratio calculation, demonstrates improved detection sensitivity of microvasculature while preserving axial resolution.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Figure 1: Ratio Analysis Calculation
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