Biological Imaging Studies Use X-Ray Phase Contrast Technologies

In the past century,traditional X-ray imaging based on beam attenuation plays an important role in various disciplines,including but not limited to medicine,material engineering,informatics and life science.With the advances in x-ray generation and detection technologies,X-ray phase contrast imaging shows great promise in expanding the horizon of current X-ray applications.Both theoretical and experimental researches reveal that X-ray phase contrast imaging is able to simultaneously provide absorption,refraction and scattering contrast images of the scanned sample.Compared to the conventional method,X-ray phase contrast imaging substantially enhances the image contrast,especially for materials with low atomic numbers,and thus is attractive for biological studies.Investigations have shown that when hard X-ray passes through samples of light elements,the phase change of X-ray is thousands of times higher than the absorption change.As such,X-ray phase contrast imaging is theoretically more sensitive and accurate in imaging of biological samples than the traditional X-ray imaging.The study of X-ray phase contrast imaging can be traced back to the 1990s.In this dissertation,we carried out researches based on two different kinds of X-ray phase contrast imaging technologies,transmission hard X-ray Zernike phase contrast microscopy and X-ray grating phase contrast imaging.Cell is the basic unit of the life activities.The research on three-dimensional cell imaging with a nanometer spatial resolution is one of the most important topics in the field of cell biology.For example,many different imaging techniques have been used to study the structure and morphology of different species of pollen grains.However,these imaging techniques have various limitations on obtaining the high resolution of a whole pollen grain.In the case of the optical microscope,the resolution is limited by the wavelength of the visible light.Another widely used instrument is the electron microscope(EM).Its drawback is that it cannot get a real 3D structure.This dissertation demonstrates that the Transmission X-ray Microscope(TXM)can get 3D ultrastructure of a whole rice pollen at high spatial resolution without sectioning,and obtain the volume percentage of each kind of organelles rapidly.This technique bridges the resolution gap between optical and electron microscopy.Regarding the imaging research,the use of X-ray can be divided into two categories:soft and hard X-ray microscopy.Due to the high depth of focus and the strong penetration power,the hard X-ray can overcome the shortage that soft X-ray cannot imaging most eukaryotic cells,whose typical dimensions are larger than 10?m.Beijing Synchrotron Radiation Facility built a zone plate based hard X-ray Microscopy beamline and a station that may reach 30 nm of spatial resolution.Based on the beamline 4W1A,we have carried out experiments to image rice pollen cells and developed methodology of transmission X-ray microscope.Another X-ray imaging technology----X-ray grating phase contrast imaging has substantial improvements in recent years.National Synchrotron Radiation Laboratory has independently designed one X-ray grating interferometer system,and carried out systematic researches on theoretical testing and small animal imaging.In this dissertation,we performed imaging experiments of a fresh cherry tomato and a dry umeboshi by using X-ray Talbot-Lau interferometer.Absorption,refraction and scattering contrast images were provided from a single set of projection images efficiently.There are different structural information in these three images which can help to realize the structure characteristics of the sample.Through comparing fruits images with animal tissues images,we found that X-ray grating interferometer have more advantages on fruits nondestructive testing(NDT).The main researches and innovations of the dissertation are as follows:1.A new phase shift information separation methods was put forward.We introduced the application and development of different kinds of X-ray imaging technologies and focused on transmission hard X-ray Zernike phase contrast microscopy and X-ray grating phase contrast imaging.We expounded some information separation methods and experiments skills of X-ray phase contrast imaging and put forward a new method which can separate phase contrast information easily and quickly on Transmission X-ray microscopy by using double frequency grating with reference to differential interference contrast.2.Methodology of Transmission hard X-ray Zenike phase contrast microscope was developed here.We developed one kind of cell imaging method on Transmission X-ray Zenike phase contrast microscope.We figured out a suitable cell preparation process and finished pollen imaging experiments on the Beamline 4W1A of the BSRF.After reconstruction and segmentation from a series of two-dimensional projections,a 3D tomography of a whole rice pollen grain about 35?m was presented with the resolution of?100nm.3.3D analysis of the rice pollen grain through X-ray imaging.The different subcelluar structures of rice pollen grain were precisely obtained from 3D reconstruction slices,including aperture,lipid body,mitochondrion,nucleus and vacuole.The whole rice pollen cell and the distribution of organelles are presented in the 3D figures.Furthermore,quantitative information about the distribution of the cytoplasmic organelles and the volume percentage of each kind of organelles was obtained,the lipid body occupies the highest volume percentage,i.e.98%.Mitochondria and vacuole occupy 2.37%and 3.54%of the pollen volume,respectively,and the volume of the nucleus is about 2.25%of the entire cellular volume..4.NDT of fruits by using X-ray grating phase contrast imaging.Even X-ray grating contrast imaging was treated as a prospect technology on Medical imaging,but it developed slowly in these years as the produced high doses beyond people's acceptance.Based on X-ray grating interferometer,we performed imaging experiments of a fresh cherry tomato and a dry umeboshi.Compared with the traditional X-ray image,X-ray grating interferometer provided much more useful structure information.The obvious advantages showed on this research demonstrated that we should give priority to fruit NDT than animal imaging.