Robust quantitative single-exposure laser speckle imaging with true flow speckle contrast in the temporal and spatial domains

TL;DR

This paper introduces a robust method for laser speckle contrast imaging that accurately measures flow speed from single-exposure data by correcting for noise and static scattering, applicable across various speckle statistics.

Contribution

The authors develop a new true flow speckle contrast technique that improves linear sensitivity and accuracy in flow speed measurement, overcoming limitations of conventional contrast methods.

Findings

Enhanced linear sensitivity of flow index from 0 to 40 mm/s

Accurate flow speed recovery despite static scattering layers

Spatial contrast more susceptible to static scattering than temporal contrast

Abstract

A systematic and robust laser speckle contrast imaging (LSCI) method and procedure is presented, covering the LSCI system calibration, static scattering removal, and measurement noise estimation and correction to obtain a true flow speckle contrast and the flow speed from single-exposure LSCI measurements. We advocate to use as the speckle contrast instead of the conventional contrast K as the former relates simply to the flow velocity and is with additive noise alone. We demonstrate the efficacy of the proposed true flow speckle contrast by imaging phantom flow at varying speeds, showing that (1) the proposed recipe greatly enhances the linear sensitivity of the flow index (inverse decorrelation time) and the linearity covers the full span of flow speeds from 0 mm/s to 40 mm/s; and (2) the true flow speed can be recovered regardless of the overlying static scattering layers and the type of speckle statistics (temporal or spatial). The fundamental difference between the apparent temporal and spatial speckle contrasts is further revealed. The flow index recovered in the spatial domain is much more susceptible to static scattering and exhibit a shorter linearity range than that obtained in the temporal domain. The proposed LSCI analysis framework paves the way to estimate the true flow speed in the wide array of laser speckle contrast imaging applications.