Abstract
Laser Doppler holography (LDH) is a full-field interferometric imaging technique recently applied in ophthalmology to measure blood flow, a parameter of high clinical interest. From the temporal fluctuations of digital holograms acquired at ultrafast frame rates, LDH reveals retinal and choroidal blood flow with a few milliseconds of temporal resolution. However, LDH experiences difficulties to detect slower blood flow as it requires to work with low Doppler frequency shifts which are corrupted by eye motion. We here demonstrate the use of a spatio-temporal decomposition adapted from Doppler ultrasound that provides a basis appropriate to the discrimination of blood flow from eye motion. A singular value decomposition (SVD) can be used as a simple, robust, and efficient way to separate the Doppler fluctuations of blood flow from those of strong spatial coherence such as eye motion. We show that the SVD outperforms the conventional Fourier based filter to reveal slower blood flow, and dramatically improves the ability of LDH to reveal vessels of smaller size or with a pathologically reduced blood flow.
Highlights
Retinal motion caused by fixational eye movements and pulsatile swelling of the choroid prove challenging in ophthalmic imaging
Laser Doppler holography (LDH) is a full-field interferometric imaging technique recently applied in ophthalmology to measure blood flow, a parameter of high clinical interest
LDH experiences difficulties to detect slower blood flow as it requires to work with low Doppler frequency shifts which are corrupted by eye motion
Summary
Retinal motion caused by fixational eye movements and pulsatile swelling of the choroid prove challenging in ophthalmic imaging. A technique based on the unfocused transmission of plane or diverging wave instead of the conventional focused emissions [14], has allowed the parallel measurement of blood flow, increasing the acquisition frame rate by more than an order of magnitude. This subsequently allowed to use spatio-temporal analysis of the Doppler fluctuations to filter tissue motion [15, 16], as it is done in x-ray computed tomography (CT) [17], and magnetic resonance imaging (MRI) [18].
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