Quantitative, depth-resolved determination of particle motion using multi-exposure, spatial frequency domain laser speckle imaging

Abstract

Laser Speckle Imaging (LSI) is a simple, noninvasive technique for rapid imaging of particle motion in scattering media such as biological tissue. LSI is generally used to derive a qualitative index of relative blood flow due to unknown impact from several variables that affect speckle contrast. These variables may include optical absorption and scattering coefficients, multi-layer dynamics including static, non-ergodic regions, and systematic effects such as laser coherence length. In order to account for these effects and move toward quantitative, depth-resolved LSI, we have developed a method that combines Monte Carlo modeling, multi-exposure speckle imaging (MESI), spatial frequency domain imaging (SFDI), and careful instrument calibration. Monte Carlo models were used to generate total and layer-specific fractional momentum transfer distributions. This information was used to predict speckle contrast as a function of exposure time, spatial frequency, layer thickness, and layer dynamics. To verify with experimental data, controlled phantom experiments with characteristic tissue optical properties were performed using a structured light speckle imaging system. Three main geometries were explored: 1) diffusive dynamic layer beneath a static layer, 2) static layer beneath a diffuse dynamic layer, and 3) directed flow (tube) submerged in a dynamic scattering layer. Data fits were performed using the Monte Carlo model, which accurately reconstructed the type of particle flow (diffusive or directed) in each layer, the layer thickness, and absolute flow speeds to within 15% or better.

Spatial versus temporal laser speckle contrast analyses in the presence of static optical scatterers

“…4(a)] and the sensitivity of speckle contrast decreased with an increase in TLT [ Fig. Collectively, these results strongly suggest the potential of temporal LSI at a single-exposure time to assess the changes in blood flow even in the presence of substantial static optical scattering, which can ultimately be combined with methods to improve the localization of speckle contrast such as spatial frequency domain 25,26 or magnetomotive techniques. With temporal speckle contrast analysis (Fig.…”

Momentum transfer Monte Carlo for the simulation of laser speckle imaging and its application in the skin

“…Here, we used a modified version of the C# Command Line Monte Carlo model developed by the Virtual Photonics Initiative at Beckman Laser Institute to track photon scattering using a discrete absorption weighting scheme [34][35][36][37][38]. We calculate the momentum transfer that occurs at each scattering event of a simulated photon [39][40][41]. All photons have a momentum (ρ), described by ρ = ħk, where ħ is the reduced Planck's constant and k the wavenumber, which has both a magnitude and a direction.…”

Spatial frequency domain imaging in 2019: principles, applications, and perspectives

“…8(b)]. 76 , [80][81][82] The concept has been extended to real-time measurements using SSOP combined with speckle flow measurement into coherent-SSOP (c-SSOP), which has been validated onto arm-cuff occlusions in human subject and is now tested clinically. 83,84…”