Research On Grating Based X-ray Phase-contrast Imaging And Related Techniques

X-ray phase-contrast imaging, which uses phase shift as the imaging signal, may provide remarkably improved contrast over conventional absorption-based imaging for weakly absorbing samples, such as biological soft tissues and fibre composites.Within all the various x-ray phase contrast imaging techniques, the method using an x-ray Talbot-Lau interferometer with a conventional low-brilliance x-ray tube is regarded at present as the most popular and the most widely used strategy, because it showed that phase-contrast x-ray imaging can be successfully and efficiently performed with a conventional, low-brilliance x-ray source, actually solving the problems that impaired a wider use of phase-contrast in x-ray radiography and tomography.However, many defects and problems exist in the present x-ray phase contrast imaging technique with Talbot-Lau interferometer, which prevent its wide usage in clinical diagnose, industrial nondestructive test and other areas, this doctorial dissertation was carried out in the hope of overcoming some weaknesses and also in the hope of trying to improve this technique in the following way.1. Designing and building a grating based x-ray phase contrast imaging setup.We designed and built a new grating based x-ray phase contrast imaging system in the University of Science and Technology of China, during the project, a Lab VIEW based x-ray phase contrast imaging software platform was developed, which covered instrument control, automatic image acquisition, data post-processing and other related function modules. Compared with the currently popular x-ray phase contrast imaging system in the world, the major difference of this setup is that the phase signal is carried in the geometric moire fringe introduced by absorbing gratings with large period (around50μ m), some advantages therefore are accessible with this system:(1) Easy to realize high energy and large field x-ray phase contrast imaging with an conventional x-ray tube;(2) All the photons with different wavelengths emitted by the x-ray tube can well meet the requirements of the imaging system.(3) This system can work well with the X-ray tube in a large range of accelerating voltage;(4) This x-ray imaging system is not sensitive to mechanical vibration and external thermal expansion.2. Experimental research based on this x-ray phase contrast imaging system.(1) The experiment with PMMA cylinder confirmed the system’s accuracy and correction of the experimental technique;(2) In industrial nondestructive test area, the experiment research implied that grating based x-ray phase contrast imaging has strong detail resolving power for materials made up of low-Z elements, for example, the SU8photoresist.3. New methods and techniques in grating-based X-ray phase contrast imaging(1) Based on the built system, we introduced a flexible dual energy x-ray phase-contrast imaging strategy, advantage of which is that, theoretically speaking, any two distinct energy spectra within the voltage scope of the imaging system can be utilized to perform the dual energy imaging, great convenience is therefore promising.(In the previously reported dual energy x-ray phase-contrast imaging technique with Talbot-Lau interferometer, the two adopted energy spectra have to be carefully chosen in order to well match the working energy of the phase grating, this method thus has low maneuverability in practical experiments.)(2) We demonstrated primary experimental research on the use of integrating-bucket phase measuring method to retrieve phase information in grating based x-ray phase contrast imaging, compared with the currently popular phase-stepping technique, advantage of integrating-bucket strategy is that fast/ultra-fast phase measurement is available, which is highly demanded in future clinical application, moreover, integrating buckets method can combine very well with phase contrast CT imaging, this would bring about some new means to realize time resolved x-ray phase contrast tomography with high throughput synchrontron radiation.(3) We introduced a new operation on the raw data collected in phase stepping scan, cyclically shifting the sequence of the raw image, in order to change the initial phase of each pixel. Based on this novel operation, we provided a new phase unwrapping solution for one conventional background correction method. Potential advantage of this phase unwrapping strategy is that its effective phase measuring range could be tuned flexibly in some degree for example to be (-π+3,π+3], thus it would find usage in certain case because the effective phase measuring range of the currently widely used background correction method is fixed to be (-π,π].