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Rainer A Leitgeb, Cedric Blatter, Branislav Grajciar, Bilal Farooq; Reliable Orientation Independent Pulsatile Retinal Flow Assessment with Doppler OCT. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5021.
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© ARVO (1962-2015); The Authors (2016-present)
To overcome the Doppler angle dependence of single beam as well as dual beam Doppler OCT for stable quantitative retinal and choroidal blood flow measurement and fast sampling of pulsatile flow
Traditional Doppler OCT allows to determine quantitatively pulsatile blood flow if the precise orientation of the vessel is known. Thus, it is highly sensitive to motion artifacts which limits its reproducibility in clinical practice. Dual beam Doppler OCT allows to solve the axial dependence of the measured flow, but still relies on determining the vessel orientation in the en-face plane. We introduce a new fully angle independent dual beam Doppler approach: when integrating the difference velocities of both illumination channels over the vessel cross sections the resulting flow value is completely independent of the vessel orientation, both in the en-face plane as well as with respect to the Doppler angle. This dramatically improves the stability of the method with respect to motion artifacts as well as improves the precision of the determined flow value. The principle was implemented with Swept Source OCT at 100,000 A-Scans/s. Since the method operates on single tomograms, it is capable to sample pulsatile blood flow in selected retinal vessels.
We demonstrate the complete angle independence of the flow calculation in a flow phantom as well as in-vivo. Whereas the flow obtained with standard dual beam and single beam DOCT varies with the orientation of the capillary, the now flow method proofs to be fully angle independent. The only condition for the method to work is, that the scanning direction is orthogonal to the plane of incidence of the two probing beams. For circumpapillary scans we employ a Dove prism that rotates the plane of incidence during circular scan, thus keeping the condition of staying orthogonal or radial to the scanning direction for each angle. We demonstrate pulsatile blood flow in five healthy volunteers for circumpapillary scans and calculate the total retinal blood flow. The values of 30-45µl/min fit well with previously published data.
We introduce for the first time a fully angle independent measurement system for absolute and motion stable assessment of pulsatile retinal flow. The method is demonstrated in-vitro as well as in-vivo and is based on dual beam Doppler OCT. Operation at 1060nm allows assessing both retinal as well as choroidal perfusion.
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