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Jianlong Yang, Yali Jia, David Huang, Gangjun Liu; Polarization-multiplexed, dual-beam swept source optical coherence tomography angiography. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3811. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Optical coherence tomography angiography (OCTA) is a novel imaging modality that could be used to evaluate capillary dropout and neovascularization in diabetic retinopathy. In this application, a critical limitation is the narrow field of view of current commercial OCTA systems, which usually have an A-line speed of 70~100 kHz. Although faster swept sources (up to 2 MHz) are available commercially, the signal to noise ratio is limited because the beam power is limited by laser safety. A dual-beam OCT could allow the use of greater power to satisfy both speed, signal, and safety requirements.
A 100-kHz swept-source laser is employed. In the sample arm, the light is split into two orthogonal-polarized beams with a separation angle of 20 degrees by a Wollaston prism. The two beams are separated by 14 degrees on the corneal plane, corresponding to a separation of 4.2 mm on the retina (Fig. 1). The OCT images from the two beams are depth encoded. A 5-mm glass plate is used to set a constant path delay difference between the two beams. The split-spectrum amplitude &phase gradient angiography algorithm was used to compute flow signal.
The measured sensitivities for the orthogonal-polarized beams are 95 and 94 dB, respectively. With a scanning angle of 17 degrees, OCTA with a field of view of 5×5 mm2 (400×400 pixels) for each beam was captured in four seconds. By montaging the two 5×5 mm2 OCTAs from the two beams, a wide-field retinal OCTA with a field of view of about 5×8 mm2 (400×640 pixels) was obtained (Fig. 2).
Polarization multiplexing of OCT beams is an effective approach to improve the system speed without sacrificing the system sensitivity. With a dual-beam setup, capillary-resolution wide-field OCTA is possible using a 100 kHz swept laser.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Fig. 1. (A) Photography of the dual beam manipulation components in the OCTA system. (B) Schematic of the dual-beam OCTA system.
Fig. 2. (A) Overlaid structure (gray) and angiographic (red) cross-sectional OCT images from the 2 beams. (B) En face retinal OCT angiogram around the fovea by montaging the angiogram from the two beams.
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