| As the basic structure and functional unit of living organisms,cell is an important research topic in life science,the movement and change of internal structure and tissue in the metabolism of living biological cells has become a hot research topic in biomedicine.Most biological cells are transparent or translucent phase objects,and the traditional optical imaging method can only record the amplitude information of the object,so it is unable to effectively image biological cells.Digital holography,as a new imaging technology,has the advantages of high sensitivity,high resolution,rapid and non-destructive measurement,and can be widely used in medical diagnosis and microstructure detection,etc.In addition,digital holographic imaging combined with and microfluidic control technique can be effectively applied to medical detection and blood detection.Compared with conventional optical imaging,digital holography can not only obtain the amplitude information of the object but also its phase information.As compared with optical holography,the storage,reproduction and transmission for images in digital holographic imaging technology is very convenient and flexible,which can realize the rapid processing and numerical analysis on the object's phase information,and the recorded phase information can reflect the object's internal structure and refractive index distribution.So,the digital holographic imaging can be used to rapidly and efficiently perform non-invasive and non-damaging phase imaging for living biological cells.In this thesis,we investigate the changes of the internal tissue structure of living onion epidermal cells during the decay of its life period based on the spatio-temporal digital holographic microscopy.In the first part,the characteristics on image resolution and field of view in spatio-temporal digital holography are studied experimentally.Firstly,in the off-axis digital holographic imaging system,a motor-controlled linear translation stage is used to drive a resolution test target to move horizontally,and its moving speed is matched with the acquisition speed of the CCD array in the imaging system to realize digital holographic recording for the target object by spatial-temporal scanning.The scanning hologram recorded on CCD is spliced in chronological sequence by Matlab to obtain the spatio-temporal scanning synthetic hologram.Furthermore,the four-step phase shift method is used to eliminate the interference items in the spectrum of the synthetic hologram,and the phase-shifted synthetic hologram is reconstructed numerically by digital hologram reconstruction algorithm.The results show that in the splicing process of spatio-temporal digital holography,the holograms with x-y distribution are arranged in a time sequences to form a synthetic hologram with y-t distribution,so the field of view in the scanning direction in the composite hologram can be extended by lengthening the scanning duration.By comparing the reconstruction results of the resolution test target in spatio-temporal scanning holography with those in conventional static digital holography,it is obvious that the reconstruction images of synthetic holograms have higher image resolution in the scanning direction.In the second part of the thesis,the wide field of view and high resolution microscopic phase imaging for living biological cells is performed by combining digital holographic microscopy and spatio-temporal digital holography.Firstly,the experiments show that the combination of spatio-temporal digital holography and digital holographic microscopy can effectively expand the field of view and improve the image resolution.Then,the living onion cells are scanned and recorded in multiple groups during a period of time,the recorded holograms are spliced into synthetic holograms and then reconstructed numerically to obtain the dynamic phase image of living onion cells.The reconstruction images of the synthetic holograms obtained at different periods show the changes of the internal tissue structures such as nucleus and actin microfilaments in living onion cells during natural decay.Moreover,the plasmolysis occurred in the process of cell dehydration is observed in the imaging results of some onion cell samples.The experimental results show that the spatio-temporal digital holography can effectively expand the field of view and optimize the imaging resolution,and is very suitable for the real-time imaging of the internal tissues of living biological cells. |
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