Effect of backscattering in phase contrast imaging of the retina

Abstract

The observation of retinal cellular structures is fundamental to the understanding of eye pathologies. However, except for rods and cones, most of the retinal microstructures are weakly reflective and thus difficult to image with state of the art reflective optical imaging techniques such as optical coherence tomography. Recently, we demonstrated the possibility of obtaining the phase contrast of retinal cells in the eye using oblique illumination of the retina. Indeed, by illuminating the eye with incoherent oblique illumination, we obtain a secondary oblique illumination from the backscattered light which can then be used to obtain phase contrast in an effective transmission-like configuration. In this technique, a weak phase signal is modulated over an intense background. Maximizing this phase contrast is thus crucial for the image quality. Here, we investigate the parameters that affect phase contrast by modelling image formation with the backscattered light. We find that the key parameter for maximizing contrast is the intensity profile of the backscattered light. Specifically, the gradient of the profile is found to be proportional to the phase contrast. We validate the model by comparing simulations with experimental results on ex-vivo retina samples.

Noninvasive white blood cell quantification in umbilical cord blood collection bags with quantitative oblique back‐illumination microscopy

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Epi-mode tomographic quantitative phase imaging in thick scattering samples

“…Here we achieve a dramatic increase in obliquity of light incident on the target by positioning our fibers at a canted vertical angle [19], typically 45 degrees ( Fig. 1(a)), positioned 9 mm away from the center of the microscope objective, which improves phase contrast and sensitivity to fine detail [20]. The angle of the incident fibers and their horizontal distance from the source are degrees of freedom to control the effective source distribution, offering flexibility in illumination.…”

Non-Invasive High-Resolution Imaging of In Vivo Human Myelinated Axons

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