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. 2019 Sep 5;10(10):4942-4963.
doi: 10.1364/BOE.10.004942. eCollection 2019 Oct 1.

Waveform analysis of human retinal and choroidal blood flow with laser Doppler holography

Léo Puyo  1   2 , Michel Paques  2   3   4 , Mathias Fink  1   2 , José-Alain Sahel  2   3   4 , Michael Atlan  1   2
Affiliations

Waveform analysis of human retinal and choroidal blood flow with laser Doppler holography

Léo Puyo et al. Biomed Opt Express. .

Abstract

Laser Doppler holography was introduced as a full-field imaging technique to measure blood flow in the retina and choroid with an as yet unrivaled temporal resolution. We here investigate separating the different contributions to the power Doppler signal in order to isolate the flow waveforms of vessels in the posterior pole of the human eye. Distinct flow behaviors are found in retinal arteries and veins with seemingly interrelated waveforms. We demonstrate a full field mapping of the local resistivity index, and the possibility to perform unambiguous identification of retinal arteries and veins on the basis of their systolodiastolic variations. Finally we investigate the arterial flow waveforms in the retina and choroid and find synchronous and similar waveforms, although with a lower pulsatility in choroidal arteries. This work demonstrates the potential held by laser Doppler holography to study ocular hemodynamics in healthy and diseased eyes.

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Conflict of interest statement

The authors declare that there are no conflicts of interest related to this article.

Figures

Fig. 1
Fig. 1
Analysis of the dynamic changes in power Doppler signal and mean Doppler frequency shift, which supposedly yield volume and velocity, respectively. (a) and (b): power Doppler image M0(x, y) and mean frequency shift fmean(x, y) temporally averaged; the red, blue, and green ROIs mark a retinal artery (RA), a retinal vein (RV), and the background (B), respectively. (c) and (d) temporal traces of M0 and fmean in the depicted ROIs. (e) and (f): temporal traces in the same ROIs when subtracting the spatially averaged signal over the entire image, i.e. M0 − 〈M0〉x,y, and fmean − 〈fmean〉x,y. See Visualization 1 and Visualization 2 for the juxtaposed movies of M0 and fmean corrected and not-corrected from the spatial average. Removing the spatial average allows to reveal the retinal flow waveforms.
Fig. 2
Fig. 2
Dependence of the retinal arterial waveform profile upon the Doppler frequency range. All curves are obtained from the same LDH measurements, only with different processing. (a) and (b): dynamic raw power Doppler and power Doppler corrected from the spatial average for three frequency ranges: 6–10 kHz in the pink solid line, 10–20 kHz in the red dashed line, and 20–37 kHz in the deep red dotted line. (c) and (d): waveform profile averaged over three cardiac cycle with variations normalized between 0 and 1. The waveform profile calculated with the frequency band 6–10 kHz shows a pulsatile signal tainted by bulk motion (attributed by unexpected oscillations); the normalized arterial waveform calculated with the very high frequency range appears steeper due to the velocity thresholding effect.
Fig. 3
Fig. 3
Venous and arterial retinal waveforms compared to the spatial average in three examples close to the ONH. Left column: normalized waveform in a retinal vein and artery (’RV’ in blue, and ’RA’ in red), and normalized waveform of the spatial average (over the entire image) in black. As seen from the red and black dashed lines indicating the end of systole, the venous minimum is more contemporary with the retinal arterial flow maximum than with the maximum of the spatial average. See Visualization 3 and Visualization 4.
Fig. 4
Fig. 4
Mapping in three different eyes of the local blood velocity, RI, and CV indices; all images are displayed on the same gray/color scale. First row: mean Doppler frequency shift fmean(x, y). Second row: resistivity map calculated according to the Pourcelot index on the flow variations corrected from the baseline signal RIM0−〈M0〉x,y ; the RI value in the arteries is around 0.7. Third row: coefficient of variation map of the raw signal CVM0.
Fig. 5
Fig. 5
Comparison of CV maps obtained from the variation of M0 and fmean in the right and left eye of the same subject. From top to down: M0(x, y), CVM0(x, y), fmean(x, y), and CVfmean(x, y). The coefficient of variation in the optic disc differs significantly between the two methods. The arrow ’1’ and ’2’ point to areas where the Doppler broadening is undersampled and to low frequency noise, respectively.
Fig. 6
Fig. 6
Laser Doppler measurements in choroidal arteries in the macular and peripheral regions. (a) and (b): Mean frequency images with ROIs on a large choroidal artery (’CA’, purple) and the background (’B’, green). (c) and (d): Raw power Doppler signal M0 in the ROIs. (e) and (f): Power Doppler signal in the same ROIs when subtracting the spatially averaged dynamic value, i.e., M0 − 〈M0〉x,y. In the peripheral region the power Doppler signal in ’CA’ corrected from the dominant signal yields a arterial-like waveform whereas the power Doppler signal measured in ’CA’ in the macular region shows only noise. This is probably because of the higher photoreceptors/RPE density, and because the dynamic signal measured in ’CA’ in the macula is exactly like the spatial average signal.
Fig. 7
Fig. 7
Pulsatile flow in the retina and choroid. (a) Power Doppler image M0(x, y) indicating the ROIs; the red, blue, green, purple boxes mark a retinal artery and vein, the background, and a choroidal artery, respectively. (b) Mean frequency shift image fmean(x, y). (c) Waveform of M0 − 〈M0〉x,y in the ROIs. (d) Coefficient of variation map CVM0(x, y): the choroidal artery has a coefficient of variation close to the values found in retinal veins, despite exhibiting an arterial waveform profile. See the power Doppler movie in Visualization 5.
Fig. 8
Fig. 8
Retinal and choroidal arterial waveforms compared to the spatial average in three examples in peripheral regions. Left column: normalized waveform of power Doppler corrected from the spatial average in a retinal and a choroidal artery (’RA’ in red, and ’CA’ in purple), and normalized waveform of the Doppler signal spatially averaged over the entire image (’D’ in black). The dominant signal waveform has an arterial waveform, which strongly resembles that of choroidal arteries.
Fig. 9
Fig. 9
Arteriovenous differentiation in the retina and choroid. (a) and (b): mean Doppler frequency fmean(x, y). (c) and (d): coefficient of variation CVM0 revealing retinal arteries and veins. (e) and (f): color composite images obtained by merging low frequency and high (2.5–6 kHz, 10–30 kHz) power Doppler images in cyan and red, allowing identification of choroidal arteries and veins (colorbars are only indicative).
See this image and copyright information in PMC

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