# Phase-sensitive interferometry of decorrelated speckle patterns

## TL;DR

This paper introduces a novel method inspired by astronomic speckle interferometry that enables phase-sensitive imaging of decorrelated speckle patterns, allowing detection of tiny structural changes in biological tissues despite decorrelation.

## Contribution

It demonstrates that phase comparison is possible during decorrelation by using multiple images, extending phase-sensitive imaging capabilities to dynamic biological samples.

## Key findings

- Effective phase retrieval during decorrelation demonstrated with simulated data.
- Successful imaging of photoreceptor activity using phase-sensitive OCT.
- Method applicable to various phase-based interferometric imaging modalities.

## Abstract

Phase-sensitive coherent imaging exploits changes in the phases of backscattered light to observe tiny alterations of scattering structures or variations of the refractive index. But moving scatterers or a fluctuating refractive index decorrelate the phases and speckle patterns in the images. It is generally believed that once the speckle pattern has changed, the phases are scrambled and any meaningful phase difference to the original pattern is removed. As a consequence, diffusion and tissue motion below the resolution handicap phase-sensitive imaging of biological specimen. Here, we show that, surprisingly, a phase comparison between decorrelated speckle patterns is still possible by utilizing a series of images acquired during decorrelation. The resulting evaluation scheme is mathematically equivalent to methods for astronomic imaging through the turbulent sky by speckle interferometry. We thus adopt the idea of speckle interferometry to phase-sensitive imaging in biological tissues and demonstrate its efficacy for simulated data and for imaging of photoreceptor activity with phase-sensitive optical coherence tomography. The described methods can be applied to any imaging modality that uses phase values for interferometry.