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Laurin Ginner, Andreas Wartak, Matthias Salas, Michael Niederleithner, Lara Wurster, Rainer A Leitgeb; In-vivo angle independent Doppler flow calculations using synthetic subapertures in a line field OCT system. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1270.
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We demonstrate a synthetic subaperture based angle independent Doppler flow calculation, using a line field SD-OCT system. High phase stability over the volume is provided by the speed increase due to parallelization, which is necessary to apply synthetic subapertures in the aperture plane. The absolute flow component can be calculated in post processing.
A line-field spectral domain OCT system is used to image a flow phantom and healthy volunteers. At each slow scanning position four cross-sectional images are acquired at the same lateral position to perform OCT angiography and Doppler flow calculations over these four time points. Synthetic subapertures are applied in parallel and in scanning direction to study the effect of parallel and temporal acquisition. Absolute blood flow was calculated by measuring the Doppler signal in each subaperture individually and analyzing their difference.
Angle independent Doppler flow calculation worked well in the parallel direction. In scanning direction however the spatial information is mixed with the Doppler shift induced by the flow itself and makes a differentiation more difficult. We demonstrated the ability to calculate angle independent Doppler flow in the parallel dimension for a flow phantom and in-vivo retinal vasculature. Due to the relatively slow B-scan rate observation were limited to smaller capillaries in the retina.
In conclusion we demonstrate the first angle independent software based Doppler flow calculations in-vivo by using synthetic subapertures in post processing. This allows flow calculations without costly hardware separations of different detection channels as implemented in standard angle independent Doppler calculations. Absolute blood flow was calculated in smaller retinal capillaries and flow phantoms. The results are promising for future Doppler analysis on a purely post processing basis.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Fig. 1 (a) shows an intensity B-scan. The zoom-in shows a vessel and its orientation in reference to the illumination direction, resulting in the angles α1 and α2. (b) presents the en-face angiography over the red marked depth section in (a) red circles mark the segmented vessel. (c) Angiography B-scan and in (d) the color-coded phase difference tomogram between two B-scans are shown, where an upward movement can be seen encoded in red and downward movement encoded in blue.
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