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Jason Tokayer, Ou Tan, David Huang; Spatial Frequency Filtering Algorithms to Enhance the Visualization of Retinal Vessels in Doppler Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1712.
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© ARVO (1962-2015); The Authors (2016-present)
To improve the identification of retinal blood vessels using spatial frequency domain filtering for Fourier-domain optical coherence tomography (FD-OCT).
Normal eyes were scanned using the RTVue FD-OCT system (Optovue, Inc. Fremont, CA), which performs 26,000 axial scans per second and has 5-micron depth resolution. A double circle scanning protocol (DCSP) centered at the optic disc was used with diameters 3.4 mm and 3.75 mm, respectively. After removing bulk motion artifacts, we employed both the standard phase-resolved (PR) algorithm and spatial high-pass filtering to detect flow in retinal vessels.
Accurate vessel centers are required for Doppler angle using DCSP. In many cases, the PR method fails to illustrate a clear image of a vessel on both circles. In these cases, spatial frequency filtering can be used to enhance vessel identification on one of the frames. On the attached images the vessels labeled 1 and 2 can be clearly identified using spatial-frequency filtering, whereas for the phase-resolved method vessel 1 has irregular shape and vessel 2 cannot be seen at all.
Spatial Frequency high-pass filtering can be used to improve the visualization of some retinal vessels near the optic disc. In contrast to the PR algorithm, the high-pass filtering algorithm is phase-insensitive and is therefore more robust to high system phase noise. Spatial frequency filtering may provide a method for calculating Doppler angle in cases with noisy PR signal.
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