Research On Erythrocyte Inline Digital Holographic Reconstruction

Blood detection has always played an important role in the diagnosis and treatment of clinical diseases.As the largest number of blood cells,changes in the number and morphology of erythrocytes are closely related to the physiological and pathological changes of the human body,so erythrocyte detection has become an important part of blood routine detection.The current blood routine detection technology mainly includes qualitative observation of blood cell morphology based on microscopic examination and quantitative measurement of blood cell parameters represented by electrical impedance method,light scattering method and flow cytometry.However,there is a lack of a qualitative and quantitative detection in one,easy operation,small and portable automated blood cell detection device,to meet the needs of application scenarios such as home doctor visits.The digital holographic imaging technology that has emerged in recent years,uses image sensors to record cell holograms,and by means of computers,numerical reconstruction was completed.It can realize clear three-dimensional imaging of microscopic cells with a large field of view and has unique advantages such as quantification,non-damage,simple hardware structure,and low cost.Especially,it has great potential in combining cell morphology observation and parameter measurement,and has been widely concerned.Numerical reconstruction is the key to obtain clear and accurate cell reconstruction images.This article has carried out a comprehensive and systematic analysis and research on erythrocyte holograms reconstruction,reconstruction algorithms,reconstruction distance,reconstruction size and other factors that affect the reconstruction quality,the method to obtain best reconstruction distance,objective quality evaluation of the reconstruction target,the reconstruction speed and other aspects.Firstly,the theory of digital holographic imaging is explained,and three classical reconstruction algorithms of Fresnel,Angular Spectrum and Convolution reconstruction are derived.The algorithms are programmed on the MATLAB platform and the programming correctness is verified.Then two methods to obtain the best reconstruction distance,the formula method and the auto focus method,are introduced.Taking erythrocyte holograms taken by the inline digital holography device as an example,after determining auto-focusing representative area according to focusing results of different positions and different sizes,a comparative experiment is conducted on two acquisition methods.Combined with algorithm transfer function simulation experiment,the effects of reconstruction algorithm,reconstruction distance and reconstruction size on the quality of erythrocyte reconstruction image are discussed.Finally,considering algorithm reconstruction performance evaluation,two indexes principle of erythrocyte reduction and image clarity are expounded,and applied to the quality evaluation of reconstruction image.The algorithm reconstruction speed is combined to comprehensively evaluate the algorithms.The experimental results show that the best reconstruction distance obtained by the auto focus method is more accurate,and appropriate auto-focusing representative area is the center 512×512 size.It is found that Fresnel and Convolutional reconstruction algorithms have limitations on reconstruction size,whose maximum normal reconstruction sizes are about 512×512 and 960×960,respectively.However,Angular Spectrum reconstruction algorithm has no limitations on reconstruction size,and can directly realize full-scale holographic reconstruction.Therefore,a block reconstruction method is proposed to achieve full-scale normal reconstruction of erythrocyte hologram by Fresnel and Convolution reconstruction algorithms.Among three full-scale reconstruction image quality evaluations,Fresnel algorithm has the worst reconstruction effect,and the other two algorithms have better reconstruction quality.In addition,running time of Angular Spectrum algorithm is less than Fresnel algorithm,and Convolution algorithm takes the most time.Therefore,Angular Spectrum reconstruction algorithm combined with the auto focus method can realize high-quality real-time full-scale reconstruction of erythrocyte inline holograms,which lays the foundation for the subsequent application of inline hologram such as blood cells.