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Franck Jaillon, Shuichi Makita, Masahiro Miura, Yoshiaki Yasuno; Choroidal Circulation Imaging with Variable Velocity Range Dual Beam Optical Coherence Angiography. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2116.
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We have demonstrated high-penetration dual beam Doppler optical coherence angiography (DB-OCA) using 1-micrometer wavelength probe beam. This system has extremely high Doppler sensitivity and can visualize fine details of choroidal vasculature. This paper aims at demonstrating a new version of high-penetration DB-OCA which contrasts choroidal vessels according to their hemodynamics by using newly implemented feature of variable velocity range.
Eight eyes of 4 normal subjects were examined using variable velocity range DB-OCA. This system uses a probe beam wavelength of 1020 nm, with a depth resolution of 5.3 μm in tissue and an acquisition speed of 47,000 A-lines/s. Several 3D volumes (1,000 A-lines x 256 B-scans) were acquired from each subject. After signal processing, en-face Doppler signal projections of choroidal vessels were obtained. En-face projections obtained at different positions were stitched together to create a wide-field high-sensitive OCA image. Velocity maps with 4 axial velocity ranges were obtained: axial velocity < 114 μm/s, < 360 μm/s, < 653 μm/s, and < 5330 μm/s.
In 6 eyes out of 8, distinguishable choroidal vasculatures were visible between measurements obtained with 4 different velocity ranges. Highest-velocity image is sensitive to high flow choroidal vessels (Fig. 1a) such as short posterior ciliary arteries. By decreasing the velocity range, small size choroidal vessels with low blood flow forming a more complex capillary network appear as shown in Fig.1b to 1d. In the remaining 2 eyes, high-flow vessels were visible but low-flow choroidal vessels were not discernible for the smallest velocity range case.
We have seen that high-penetration DB-OCA with variable velocity ranges allows non-invasive discrimination of choroidal vessels according to their blood velocity. Using all images acquired with different velocity ranges will provide a more complete visualization of choroidal vessels including its structural and velocity properties.
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