Research On Laser Speckle Contrast Imaging Technology Through Scattering Media Based On Wavefront Modulation Technology

Laser speckle contrast imaging technology has been developed into a wide-field velocity imaging technology with real-time,non-scanning,non-contact,high spatial and temporal resolution,and low cost.It has a wide range of applications in parameter detection in biological tissue physiology,disease detection,and drug evaluation.However,the high scattering property of biological tissue makes the application of laser speckle contrast imaging technology limit to the velocity information of the surface layer,which leads to the undetectable blood flow information of deep tissue.Therefore,it becomes more important to achieve laser speckle contrast imaging of deep tissue.The main reason for limiting the depth of imaging in biological tissues is due to the scattering of light.Scattering media(such as biological tissue,etc.)disturbs the propagating wavefront,resulting in ambiguous imaging.In this paper,the phase modulation characteristic of the liquid crystal spatial light modulator is used to compensate the wavefront disturbed by scattering media to minimize the influence of the scattering light.Further more,combining the laser speckle contrast imaging technology,the map of the relative velocity changes through the scattering media is obtained.The main results of this thesis include:(1)A method of imaging the relative velocity changes of moving objects through scattering media by combining wavefront modulation technique with laser speckle contrast analysis method is proposed.It utilizes the phase modulation characteristic of the liquid crystal spatial light modulator to compensate the wavefront disturbed by scattering media.Combining the laser speckle contrast analysis method,the velocity of the moving object through scattering media is detected.(2)A laser speckle contrast imaging system based on wavefront modulation technology is built,which is mainly composed of laser wide field illumination,liquid crystal spatial light modulator(LC-SLM)wavefront modulation and CCD camera image acquisition unit.Among them,the wide field illumination unit uses a helium gas laser as the illumination source,which passes through the beam expanding system and becomes the wide field uniform illumination.The wavefront modulation unit adopts an electrically addressable reflective pure phase liquid crystal spatial light modulator in the visible light band as the main modulation device.The phase modulation characteristic is used to modulate the wavefront to correct the distortion caused by scattering media.The image acquisition unit adopts the area array CCD camera in the visible light band as the light detector component for optimization and imaging.(3)A software system for wavefront modulation and laser speckle contrast imaging is developed,which mainly includes the control program part of the liquid crystal spatial light modulator,the image acquisition program part of the CCD camera and the genetic optimization algorithm part.Among them,the phase map is loaded on the liquid crystal spatial light modulator by the control program part;the camera parameter configuration and image acquisition,display and preservation are done by the image acquisition program part of the CCD camera;the genetic optimization algorithm mainly includes the fitness calculation,selection operator,crossover operator and mutation operators,et al.The software system and the optical imaging system form a closed-loop feedback wavefront modulation system.After iterative optimization,the correlation coefficient between the final optimized image and the preset target image can reach 0.88,which results in a phase map that compensates the wavefront distortion caused by scattering media.(4)The imaging system performance analysis and system parameter optimization are carried out.The moving rigid body experimental model and the fluid experimental model are used to verify that the imaging system can realize the velocity imaging of moving objects through scattering media,and the experimental results show that the measured relative velocity index is linear with the actual velocity.