Study Of Low-Dose 3D Imaging Of Biomaterials With Synchrotron Radiation

Since Rontgen discovered X-rays while studying cathode rays in 1895,X-rays have been widely used in the field of imaging due to short wavelength and strong penetrating ability.X-ray imaging can be used as a non-destructive and high-resolution imaging method,and it can achieve three-dimensional imaging of thick samples,making up for many shortcomings of traditional optical microscope imaging and electron microscopy imaging and filling the gap between them.At present,the third-generation synchrotron radiation source,which provides soft X-rays and hard X-rays with stable and superior performance,has been continuously developing.Compared to ordinary light sources,synchrotron radiation has the characteristics of high collimation,high brightness and wide spectrum,and has been widely applied in physics,materials science,biology and environmental science fields.Synchrotron radiation X-ray imaging is an important method for studying the three-dimensional structure and organization of biological samples.However,the imaging of biological samples currently has some problems that need to be improved.For example,how to decrease the radiation damage of the sample;how to image aqueous sample since the X-ray absorption of the biological sample is poor;and how to choose proper parameters of the three-dimensional reconstruction algorithm.In view of the above issue of synchrotron radiation X-ray imaging,using the Shanghai synchrotron radiation source research platform,a three-dimensional imaging study of cells and blood vessels has been carried out.The main contents are described as followings:(1)Study on reconstruction effects of three-dimensional reconstruction EST algorithm parameters.Combined with the cell morphology of the yeast needed for subsequent experiments,a three-dimensional reconstruction sample model was created in MATLAB software and a series of projections were generated.The three-dimensional reconstruction of the sample was performed based on an equally sloped tomography reconstruction algorithm(EST),and three-dimensional reconstruction of different numbers of projections,whose numbers varies from 6 to 360 was performed.The reconstruction of these different numbers of projections was performed.After the reconstruction,the reconstruction results were compared with the original model.The influence of the number of reconstruction projections on the reconstruction error was analyzed,and the missing wedge effect that would influence sample morphology after reconstruction was explored.For EST reconstruction,as the number of projections increased and reached a certain value,the error between the reconstruction structure and the original model remained constant.There would be significant errors and more pronounced artifacts in the presence of misssing wedges.The missing wedge caused the shape of the reconstructed sample to have a certain degree of deformation,which is difficult to be corrected by increasing the number of projections within the non-missing wedge area.In addition,the curved structure perpendicular to the missing projection surface would be difficult to distinguish.The simulation provided guidance for the subsequent reconstruction of the experiment.(2)Three-dimensional low-dose scanning transmission X-ray microscopy(STXM)and three-dimensional reconstruction of scanning CDI(ptychography)of fission yeast cells.Combined with the STXM experimental method and equally sloped projection reconstruction method,low-dose and high-resolution 3D reconstruction of fission yeast fission yeast was performed.The projection angle was distributed from 58.0° to-72.6°with a pixel resolution of 30nm.After EST reconstruction,the cylindrical shape,distorted splitting structure and internal pore structure could be observed.The radiation dose of the sample was reduced using the scanning transmission imaging method and the EST reconstruction algorithm.Based on the STXM experimental platform,a three-dimensional imaging study of yeast CDI scanning was performed.Scanning CDI imaging was performed according to the equally sloped projection angle selected in the STXM experiment.After obtaining the diffraction data,the phase of the scanning CDI was restored and the resolution of the pixel in real space is 4.69 nm.The modulus values and phases of the complex matrix elements reflect the X-ray absorption and electronic density information of the sample respectively.The projection of modulus and the projection of phase were reconstructed by EST algorithm,and the results of the two reconstructions were compared.Results showed that the modulus-reconstruction results had higher resolution and reflected more detail,and the structure boundary of phase-reconstruction results was clearer.(3)Synchrotron radiation X-ray whole field transmission imaging studies of mouse blood capillary.The blood capillary of mice was studied using synchrotron radiation hard X-rays,and 1080 projections were acquired under 12 keV energy for CT three-dimensional reconstruction to achieve three-dimensional submicron imaging of blood vessels.Coaxial phase-measuring X-ray imaging of blood vessels was performed during the experiment,demonstrating the advantage to absorption-weighted imaging referring to weakly absorbing samples.What is more,three-dimensional imaging of single-cell entrapped capillaries was achieved using.In addition,the whole-field transmission imaging experiment was performed on water-containing blood vessels.The aorta of the water-containing blood vessels and the surrounding water environment were not well-weighed,while the capillary vessels were reconstructed well.A similar"bamboo" structure was found inside.This proves that this kind of structure exists in the in situ aqueous capillary.