Blood Flow Visualization by Means of Laser Speckle-Contrast Measurements under the Conditions of Nonergodicity
The influence of stationary structural inclusions in inhomogeneous strongly scattering media such as biotissues on the results of speckle-contrast measurements using temporal and spatial methods of image processing by means of laser speckle-contrast imaging is investigated. The limits of applicability of the method of laser speckle-contrast imaging are established in detail for the case in which ergodicity conditions are not fulfilled. Based on model experiments, it is demonstrated that an increase in the number of stationary scatterers relative to that of the dynamic ones in the sampling volume introduces substantial error into the results of spatial and temporal processing of speckle images for given exposure time of the detector. At the same time, analysis of spatial and temporal speckle contrasts, the values of the coefficient of speckle dynamics, along with the results of Monte-Carlo simulation of the sampling volume, revealed that the presence of a relatively thin, up to 30% of entire volume, static layer does not introduce considerable changes into the results of measurements by the method of laser speckle-contrast imaging. The exposure time of the camera, along with the number of frames used for image processing, can be varied and chosen individually for each experiment. The developed algorithms of spatial and temporal processing of images obtained by the method of laser speckle-contrast imaging were tested in the experiments on transcranial visualization of the cerebral blood flow of a mouse.
Univeristy of Oulu
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