Can laser speckle flowmetry be made a quantitative tool?

Abstract

The ultimate objective of laser speckle flowmetry (and a host of specific implementations such as laser speckle contrast analysis, LASCA or LSCA; laser speckle spatial contrast analysis, LSSCA; laser speckle temporal contrast analysis, LSTCA; etc.) is to infer flow velocity from the observed speckle contrast. Despite numerous demonstrations over the past 25 years of such a qualitative relationship, no convincing quantitative relationship has been proven. One reason is a persistent mathematical error that has been propagated by a host of workers; another is a misconception about the proper autocorrelation function for ordered flow. Still another hindrance has been uncertainty in the specific relationship between decorrelation time and local flow velocity. Herein we attempt to dispel some of these errors and misconceptions with the intent of turning laser speckle flowmetry into a quantitative tool. Specifically we review the underlying theory, explore the impact of various analytic models for relating measured intensity fluctuations to scatterer motion, and address some of the practical issues associated with the measurement and subsequent data processing.

Statistical studies on optical vortices in dynamic speckle fields

“…In this work we have related the observed dynamics of the optical vortices in a simulated speckle field, to the type and rate of decorrelation in the field. This decorrelation is a representative of the dynamic behavior of scatterers that, under coherent illumination, produced the speckle field under observation [29].…”

“…The second behavior was one that displayed a Gaussian decorrelation line shape. This decorrelation behavior has generally been understood to be associated with ordered dynamics [29]. The third behavior examined, Lorentzian decorrelation, is linked to Brownian dynamics.…”

‘Go with the flow ’: A review of methods and advancements in blood flow imaging

“…The time-varying component of speckle may be quantified by comparisons of like pixel intensities recorded in successive scans of the subject, thus forming 2D maps of flow across the region of interest. A successful approach was developed using laser speckle contrast analysis (LASCA), which assumes that (considering a Lorenztian flow profile) the speckle contrast could be related to correlation time t C (and hence RBC V ) [110,112]:…”

Improved Cerebral Blood Flow Measurement with Multiexposure Speckle Imaging

“…As such, the exact quantitative relationship between speckle contrast and blood flow velocity has not been precisely defined. 7,8 The sensitivity of LSCI to nonflow parameters is particularly problematic in long-term studies where nonflow parameters are more likely to vary between imaging sessions.Recently, traditional single-exposure LSCI was extended with a multiexposure speckle imaging (MESI) protocol that improved quantitative accuracy in microfluidic flow simulations and in vivo imaging in rodents. 9,10 Using improved mathematical models and instrumentation to acquire speckle contrast images at multiple, defined exposures, MESI accurately estimates flow changes associated during acute ischemic stroke, contrary to the underestimates of flow changes associated with traditional single-exposure LSCI.…”

“…As such, the exact quantitative relationship between speckle contrast and blood flow velocity has not been precisely defined. 7,8 The sensitivity of LSCI to nonflow parameters is particularly problematic in long-term studies where nonflow parameters are more likely to vary between imaging sessions.…”