Noise Effects And Correction Methods In Laser Speckle Contrast Imaging

Laser speckle contrast imaging method as an optical imaging method can be used for detecting blood flow,with advantages of non-contact,high spatial and temporal resolution and simplicity,which has been applied to the field of monitoring the retina and cerebral blood flow.However,study about the effect of noise in imaging system and effect of the speckle dynamic changes for multiple scattering in biological tissue are not thorough.There are still many problems need to be solved.This article discussed the effect of CCD noise in laser speckle contrast imaging by theoretical analysis,numerical simulation and experimental measurement.Shot noise of CCD in laser speckle contrast imaging system as inherent noise of CCD,which can't be eliminated,is the main noise source of imaging system.Firstly,we create a shot noise theory model in order to study the effect of shot noise for the measurement of speckle contrast value.Due to the shot noise model,we consider that shot noise increases speckle imaging contrast and introduce an offset in the SC value,and the value of the offset will increase while the light intensity decrease.After that,we use dynamic speckle simulation method based on copula method to create speckle patterns.The results of contrast analysis of these patterns verify the validity of the theoretical analysis.Further experimental results show that under the condition of weak light the effect of shot noise for measurement accuracy is more serious.Then we get the value of convert gain by experiments,with which we can calculate the value of shot noise.Finally,combining the dark correction and shot noise correction we achieve a correction formula of speckle contrast.Considering the correction formula of speckle contrast can be used in the research field of multiple scattering in speckle contrast imaging.In this part,we do the research by theoretical formula derivation and experimental measurement.First of all,we derive a theoretical calculation formula of diffuse speckle contrast analysis based on the diffuse correlation spectroscopy.Then we set experiment device of diffuse speckle contrast imaging,and corrected the shot noise effect for the result of experimental measurement.We calculate the diffusion coefficients of two relationships,one is the relationship between the speckle contrast and the source-detector separation,the other one is the relationship between the speckle contrast and the exposure time,by fitting and comparing the results with the theoretical value.The results verify the effectiveness of diffuse speckle contrast imaging which can be used for quantitative measurement of scattering particle movement information.In this paper,the research results provide reference to improve measurement accuracy of laser speckle contrast imaging method.