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Hansford C. Hendargo, Al-Hafeez Dhalla, Ryan P. McNabb, Joseph A. Izatt; Overcoming High Flow Rate Imaging Limitations in Doppler Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1756.
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© ARVO (1962-2015); The Authors (2016-present)
Doppler optical coherence tomography (DOCT) allows for quantitative measurement of blood flow in the retinal vasculature. By summing flow rates from all vessels radiating from the optic nerve head, the total retinal blood flow may be estimated. Previous DOCT methods based on commercially available spectral-domain OCT (SDOCT) systems were unable to measure high speed flows in the major branch retinal arteries due to signal washout and phase wrapping artifacts. We theoretically and experimentally demonstrate the potential of high-speed swept-source OCT (SSOCT) combined with image processing to overcome both of these artifacts, allowing inclusion of all retinal vessels in quantitative analysis of total retinal flow.
A high-speed SSOCT system based on a commercially available miniaturized swept laser source (Axsun, 1050 nm, 100 kHz sweep rate) was used for this study. DOCT data from that system was compared with that obtained with a custom high-speed SDOCT system which employed a superluminescent diode (Superlum, 830 nm) and a line-scan camera (Basler, 100 kHz). DOCT comparison experiments used a 1% intralipid flow at velocities varying from 0 - 176 mm/sec. Phase unwrapping was performed with a quality-guided phase map based on minimum gradients.
The highest detectable velocity in OCT is fundamentally limited by the detector integration time per wavelength sampled. Due to the rapidly sweeping wavelength, the detectable velocity range in SSOCT is several orders of magnitude larger than in SDOCT systems operating at the same acquisition rate. Experimental measurements show that even a high-speed SDOCT system suffered fringe washout artifacts, degrading average velocity measurements as low as 80 mm/sec. The SSOCT system accurately measured flow up to the maximum speed tested (176 mm/sec) after phase unwrapping.
We demonstrated the potential of Doppler SSOCT to remove fringe washout effects in fast flow rates to overcome limitations in quantifying flow in major retinal vessels. This technique will be applied to demonstrate the ability to measure high speed total retinal blood flow in all retinal vessels.
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