Spatial And Temporal First Order Photon Correlation X-ray Imaging

In statistical optics theory,the correlation characteristics of optical field can be divided into first-order correlation characteristics and higher-order correlation characteristics.In fact,in the traditional optical imaging,only the first-order correlation effect of the light field is used,that is,the spatial or temporal correlation formed by the intensity and phase of the light field is used to obtain the information of the imaged sample.X-ray phase contrast imaging has higher resolution and higher signal-to-noise ratio than absorption imaging in biological soft tissue or lighter element materials.However,the phase contrast imaging of hard X-ray often has certain requirements for the first-order spatial coherence of the light source.For example,the In-line X-ray phase contrast imaging,the Interferometry X-ray phase contrast imaging,the Diffraction Enhanced Imaging,the Grating Differentiation Imaging and Speckle Tracking Imaging.Among them,speckle tracking method has attracted extensive attention in recent years due to its simplicity and low cost of imaging devices,high efficiency,and high phase sensitivity.However,the obstacle restricting the practical application of this method has not been solved,that is,the second-derivative effect of the phase will produce the edge enhancement effect at the sharp change of the phase of the sample and interfere with the precision of phase recovery at these positions.In the field of first-order time-dependent correlation imaging,time-subtraction angiography has always been the gold standard for the diagnosis and treatment of vascular diseases.In this method,the blood vessel image is obtained by subtraction of two frames of images in time interval by using the properties of contrast agent perfusion in time.However,due to the interference of complex motion in living organisms,this subtraction method often has more artificial artifacts and lower imaging resolution and signal to noise ratio.Therefore,the current X-ray first-order time-space correlation imaging still needs further development and improvement.This paper proposes an innovative solution to the shortcomings of the above Xray imaging methodology.The details are as follows:1.The imaging method and system of speckle phase contrast of X-ray sandpaper based on first order spatial light field correlation was firstly designed and successfully established in BL13 W beamline of Shanghai Synchrotron Radiation Facility.At present,the platform has verified the feasibility,effectiveness and practicability of the experimental method through a series of verification experiments.In traditional speckle tracking phase contrast imaging,either single exposure method or sandpaper stepping scanning method,the edge enhancement effect caused by the second derivative of the sample phase will interfere with the phase recovery at the abrupt phase change and worsen the imaging quality.This paper creatively proposed the double-exposed speckle tracking method based on the imaging principle.By integrating the information of the phase second derivative in the in-line X-ray phase contrast imaging,it fundamentally solved the defect of the traditional speckle imaging method that the edge enhancement effect reduced the imaging quality.By qualitative and quantitative standards,the phase information of the sample was reconstructed accurately and the image signal-to-noise ratio and resolution were significantly improved on the premise of only increasing one exposure of the data acquisition amount and radiation dose with the double-exposed method.It solves a key technical problem for the practical application and popularization of speckle tracking phase contrast imaging.2.Based on the first-order time light field correlation,this paper proposed the concept and method of moving contrast and this concept was applied to the field of X-ray angiography,namely moving contrast angiography(MCA).This method uses the signal processing method to separate the blood flow signal and the movement tissue signal as well as the stray noise signal,it is a highly sensitive imaging technique to track the movement of contrast agents in vivo.Its purpose is to reconstruct the complete perfusion trajectory of contrast agents,including constant or pulsive moving of it.Combined with the hemodynamic characteristics of each blood vessel and the phase information of the dynamic signal reflecting the time of contrast agent perfusion,MCA method can reconstruct the entire perfusion process of contrast agent.In this way,the independent enhancement imaging of arterial and venous vessels can be realized.MCA method provides another reliable choice for clinical angiography.3.The above first-order time-space correlation imaging of X-ray is a twodimensional imaging method,which needs to be combined with the corresponding CT algorithm to expand the method to three dimensions.However,due to the large amount of data required for CT imaging,it is not suitable for real-time imaging in vivo.In order to solve this problem,an X-ray stereo imaging system based on the concept of higher level spatial correlation and principle of human vision is established in this paper on the BL13 W beamline of Shanghai Synchrotron Radiation Facility.The system uses two capillaries to extract and divide the synchrotron radiation into two crossed X-ray beams,and a CCD detector is used to record two projections of the sample.The capillary scheme is simple and feasible,and the spot quality meets the imaging requirements.The calculation formula of depth information of two projectors recorded by a single CCD detector was derived,and a set of reconstruction algorithm program of stereo information was written.Numerical simulation and experimental results show that the proposed scheme has good imaging results.Compared with other three-dimensional X-ray imaging methods,X-ray stereo imaging has its own advantages and application range.It can be used as another alternative imaging method for the BL13 W beamline of Shanghai Synchrotron Radiation Facility.4.This paper also briefly introduces the second-order correlation imaging method.Because the pseudo thermal light source with controllable coherent time is generally required for the second order correlation imaging,different from the visible light,it is difficult to obtain the pseudo thermal light source for X-ray.Based on the simulation of the second order thermo-optical correlation imaging system and the compressed sensing image restoration algorithm,the paper selects the real speckle pattern of sandpaper collected by the experiment as the X-ray pseudo-thermo light source to verify the effectiveness and practicability of it in the simulation experiment of X-ray second-order correlation imaging.Simulation results show that the pseudo-thermal light field of X-ray sandpaper speckle is Gaussian.Thus,the measurement matrix meets the RIP criterion.Combined with the compressive sensing data reduction algorithm,the X-ray second-order correlation imaging method using X-ray sandpaper speckle as the experimental light source can greatly reduce the experimental complexity and the amount of data collected.This lays a foundation for the practical application of second order correlation imaging which using the X-ray sandpaper speckle as pseud-othermal light source.