Quantitative Model Of Diffuse Speckle Contrast For Extracting Multiple Parameters

Diffuse speckle contrast analysis(DSCA),i.e.,the combination of laser speckle contrast imaging(LSCI)and diffuse correlation spectroscopy,has the advantages of visualizing the deep tissue.DSCA has emerged as a powerful technique for monitoring deep tissue blood flow with the advantages of simplicity,full field and high spatio-temporal resolution.However,DSCA does not have an analytical expression to describe the relation between speckle contrast and blood flow information in the exiting studies.It is difficult to quantitatively obtain blood flow information from speckle contrast measurements and study the influence of optical property of the tissue on the measurements of blood flow information.Therefore,the quantitative model of DSCA for measuring blood flow information and extracting multiple parameters are studied by theoretical analysis,numerical calculation and experiment in this dissertation.Firstly,based on the correlation diffusion equation,the speckle contrast expressions of different velocity model(Brownian motion and ordered flow)for the homogeneous parallel plane slab and the semi-infinite medium are deduced.Therefore,the inversion optimization algorithm can be used to measure the particle diffusion coefftcient ?DB=2.14×10-8 cm2/s with a priori knowledge of optical property of the tissue(the absorption coefficient ?a and the reduced scattering coefficient ?s')and the constant factor ? by the dependence of speckle contrast on the exposure time T or the source-detector(SD)separation ?.The experimental measurements of ?DB are in agreement with the measurements of DB-Einstein=2.04×10-8 cm2/s by the dynamic light scattering method.Second,the linear approximation equation is further deduced based on the speckle contrast model.The results show that the slope ksiope of this linear approximation equation has a linear relation with ?DB and the Brownian diffusion coefficient ?DB=2.12×10-8cm2/s can be determined from the measurements of ksiope with a priori knowledge of ?a,?s' and ?·It has been demonstrated that ksiope is equal to the inverse of correlation time of the electric field autocorrelation function by theoretical analysis and numerical calculation.Therefore,we have theoretically quantified the influence of optical property on the aDB measurements based on the fact that ksiope=1/?c.The theoretical results agree well with experimental results.Finally,we develop the model of multi-distance and multi-exposure DSCA(MDME-DSCA)to obtain multiple parameters(?a,?s',?DB and ?)by DSCA.MDME-DSCA is able to decouple the large cross-talk between these parameters and further confine the solution to a smaller area.Therefore,MDME-DSCA can simultaneously obtain multiple parameters by the numerical calculation and the experiment.Besides,the sensitivity of multiple parameters of MDME-DSCA is discussed.It is found that the reduced scattering coefficient ?s' has a greater influence on the speckle contrast and the sensitivity of the absorption coefficient ?a is much less than ?s' and ?DB,which result in that the measurements of ?a has a higher error.The outcome of this dissertation can provide theoretical basis for monitoring the blood flow in deep tissue under a variety of pathological conditions.