Retinal blood flow reversal quantitatively monitored in out-of-plane vessels with laser Doppler holography

Abstract

Laser Doppler holography is a planar blood flow imaging technique recently introduced in ophthalmology to image human retinal and choroidal blood flow non-invasively. Here we present a digital method based on the Doppler spectrum asymmetry that reveals the local direction of blood flow with respect to the optical axis in out-of-plane vessels. This directional information is overlaid on standard grayscale blood flow images to depict flow moving towards the camera in red and flow moving away from the camera in blue, as in ultrasound color Doppler imaging. We show that thanks to the strong contribution of backscattering to the Doppler spectrum in out-of-plane vessels, the local axial direction of blood flow can be revealed with a high temporal resolution, which enables us to evidence pathological blood flow reversals. We also demonstrate the use of optical Doppler spectrograms to quantitatively monitor retinal blood flow reversals.

Super-Resolution Ultrasound Localization Microscopy using High-Frequency Ultrasound to Measure Ocular Perfusion Velocity in the Rat Eye

“…Reversal of blood flow with IOP elevation has been seen in human retinal arteries with central retinal vein occlusions and elevated IOP using laser doppler holography [42]. Consistent with our study, using visible light optical coherence tomography, reversal of retinal arterial blood flow was noted in 4 month old Brown Norway rats at IOP magnitudes of 50 to 60 mm Hg [43].…”

Retinal blood flow imaging with combined full-field swept-source optical coherence tomography and laser Doppler holography

“…Compared with standard fullfield laser Doppler or laser speckle contrast imaging [8][9][10], the interferometric detection in LDH enables full-field retinal blood flow imaging with higher temporal resolution [11]. The phase sensitivity in LDH additionally enables the detection of the local axial direction of blood flow, i.e., color Doppler imaging [12]. Here, we report on adapting an FF-SS-OCT setup to allow OCT and LDH imaging to be performed on a single instrument, which we used to monitor retinal blood flow and better understand the hemodynamic signals measured by both modalities.…”

“…Then only positive and negative Doppler frequency shifts can be distinguished, enabling the directional information in Fig. 2(b) [12]. With a hue-saturation-value combination of images based on the symmetry or asymmetry of the power spectrum density, directional blood flow images can be obtained [12].…”

“…2(b) [12]. With a hue-saturation-value combination of images based on the symmetry or asymmetry of the power spectrum density, directional blood flow images can be obtained [12]. Therefore, the defocused measurement allows vessels carrying upward or downward flow to be revealed with a red and blue contrast.…”

“…The LDH average spectrogram in Fig. 3(f) enables monitoring of the eye axial velocity (arrow) [12]. Bulk motion is significantly filtered in LDH thanks to the SVD filtering [17].…”