Simulative And Experimental Investigations On Principles Of In-line X-ray Phase Contrast Imaging

Compared with the conventional X-ray imaging technique based only onattenuation, X-ray phase contrast imaging, in the field of soft-tissue imaging has suchvirtues as low radiation, high visibility and so on, thus leading to widespread respectand rapid development in the past decade.Without beam restriction or optical components along the beam path, the simplestmethod mentioned in this study, referred to as in-line X-ray phase contrast imaging(XPCi), is considered as the most straightforward XPCi implementation from the labto bedside. Three parts compose the main content of this paper. Firstly, edge methodwas used to quantitatively evaluate image quality from the XPCi system. Secondly, anumerical simulation tool was developed to guide the optimization of parametersunder the XPCi system. Finally, Wiener filtering was used to improve the visibility ofinterference patterns from the XPCi system.An in-line phase contrast imaging system using micro focus X-ray source wasbuilt in the laboratory. For quantitative evaluation of the image quality, edge methodwas used to measure the modulation transfer function (MTF) of the imaging system.In order to correct the measuring errors produced by both flaws in the edge andresponse difference in the pixels, curve-fitting on the different segmentation of edgeresponse function were used, as well as tail-truncating and exponent-stretching on theline spread function. Consistency was obtained between the MTF from the edge andthe discrete value from the test card, which verified the effectiveness of the edgemethod in the MTF measurement.To obtain optimal phase-contrast results, an accurate and reliable numericalsimulation tool is needed for the optimization of parameters under the lab-equippedimaging system. The simulation tool in this study is based on the Fresnel/Kirchhoffdiffraction integral with comprehensive considerations on the source-to-sampledistance, the sample-to-detector distance, the source size, the polychromaticdistribution, the point spread function of fluorescent screen and the pixel dimension ofCMOS detector. Consistency between the profile from the numerical simulation andthat from the experiment under the same parameters has verified the validity and theeffectiveness of the simulation tool.Because of the negative effects such as noise, total point spread function and spatial resolution under the lab-equipped imaging system, the visibility of interferencepatterns was low. Firstly the Wiener filter was used to validate its feasibility inimproving the image visibility under the simulation results, and then this filter wastested under one-dimensional experiment result. The experiment profile after filteringshowed a raise in signal-to-noise ratio, in other words, the visibility of phase contrastimage was improved.