Evaluation and Correction for Optical Scattering Variations in Laser Speckle Rheology of Biological Fluids

Abstract

Biological fluids fulfill key functionalities such as hydrating, protecting, and nourishing cells and tissues in various organ systems. They are capable of these versatile tasks owing to their distinct structural and viscoelastic properties. Characterizing the viscoelastic properties of bio-fluids is of pivotal importance for monitoring the development of certain pathologies as well as engineering synthetic replacements. Laser Speckle Rheology (LSR) is a novel optical technology that enables mechanical evaluation of tissue. In LSR, a coherent laser beam illuminates the tissue and temporal speckle intensity fluctuations are analyzed to evaluate mechanical properties. The rate of temporal speckle fluctuations is, however, influenced by both optical and mechanical properties of tissue. Therefore, in this paper, we develop and validate an approach to estimate and compensate for the contributions of light scattering to speckle dynamics and demonstrate the capability of LSR for the accurate extraction of viscoelastic moduli in phantom samples and biological fluids of varying optical and mechanical properties.

Assessing blood coagulation status with laser speckle rheology

“…In addition to the effects of sample mechanics, the evolution of the g 2 (t) curve is also influenced in part by factors such as the optical properties of blood (Eq. (2) and speckle contrast [19,43,44]. We have previously demonstrated that an increase in optical scattering can accelerate the decay rate of the measured g 2 (t) curve independent of sample mechanical properties due to an increase in the number of scattering events per optical path [19].…”

“…(2) and speckle contrast [19,43,44]. We have previously demonstrated that an increase in optical scattering can accelerate the decay rate of the measured g 2 (t) curve independent of sample mechanical properties due to an increase in the number of scattering events per optical path [19]. Also, absorption of light can reduce the contribution of longer optical paths resulting slower speckle decorrelation at initial times of g 2 (t) decay.…”

“…LSR is distinct in that as it measures the viscoelastic properties of blood from time-resolved laser speckle intensity fluctuations to determine blood coagulation status in patients. We have previously demonstrated the capability of LSR for characterizing the viscoelastic properties of phantom materials, bio-fluids, and solid tissue [13][14][15][16][17]19]. In LSR, the viscoelastic properties of a material are estimated by relating laser speckle intensity fluctuations with the viscoelastic susceptibility of the surrounding medium [21,[36][37][38].…”

“…Additionally temporal averaging is performed over multiple g 2 (t) curves that evolve in time to improve the statistical accuracy of the final g 2 (t) curve. The time scale of temporal speckle intensity fluctuations was measured by calculating the speckle autocorrelation time constant, τ, computed by fitting a single exponential model function to the g 2 (t) curve measured as above and calculating time constant of exponential model function [13][14][15][16][17]19]. Because the time scale of speckle fluctuations is directly related to the viscoelastic properties of the blood sample, the speckle autocorrelation time constant, τ, of the g 2 (t) curve provided an index of clot viscoelasticity.…”

“…In this study, we have investigated and validated a new optical approach, Laser Speckle Rheology (LSR) [13][14][15][16][17][18][19], for assessing the viscoelastic properties of blood during coagulation, therefore opening the opportunity to assess the patient's coagulation state rapidly using just a few drops of whole blood.…”