Aperture phase modulation with adaptive optics: a novel approach for speckle reduction and structure extraction in optical coherence tomography

Abstract

Speckle is an inevitable consequence of the use of coherent light in imaging and acts as noise that corrupts image formation in most applications. Optical coherence tomographic imaging, as a technique employing coherence time gating, suffers from speckle. We present here a novel method of suppressing speckle noise intrinsically compatible with adaptive optics (AO) for confocal coherent imaging: modulation of the phase in the system pupil aperture with a segmented deformable mirror (DM) to introduce minor perturbations in the point spread function. This approach creates uncorrelated speckle patterns in a series of images, enabling averaging to suppress speckle noise while maintaining structural detail. A method is presented that efficiently determines the optimal range of modulation of DM segments relative to their AO-optimized position so that speckle noise is reduced while image resolution and signal strength are preserved. The method is active and independent of sample properties. Its effectiveness and efficiency are quantified and demonstrated by both ex vivo non-biological and in vivo biological applications.

Crosstalk-free volumetric in vivo imaging of a human retina with Fourier-domain full-field optical coherence tomography

“…Deformable membranes/mirrors and diffusers have also been used in scanning confocal OCT systems to achieve similar goals -to reduce speckles [44,45] or/and contribution of multiply scattered light [46]. However, unlike in scanning systems, DM does not introduce aberrations in FF-OCT when added before the interferometer because the illumination does not have to be spatially coherent as it does in confocal microscope.…”

Spatio-temporal optical coherence tomography provides full thickness imaging of the chorioretinal complex

“…Our approach is similar to the iterative weighted shift-and-add method 51 and a method that uses a modulation of the phase in the system pupil aperture by deformable mirror (DM). 52 …”

Comparative study of phase unwrapping algorithms based on solving the Poisson equation

“…When measuring the rough surface/object with interferometry, the speckle or coherent noise widely exists, such as in ESPI [70][71][72], OCT [53,[73][74][75], etc. The speckle is the result of the interference among multiple beams with random phase differences [76], which heavily degrades the fringe or image contrast.…”