Research On Medical Applications And Experimental Techniques Of X-ray Grating-Based Phase Contrast Imaging

The X-ray was discovered in 1895,and the usefulness of X-ray imaging has been recognized among many disciplines ever since.However,because the conventional X-ray imaging methods have relied on the absorption of X-ray,weak absorbing structures,such as biological soft tissues,cannot be imaged with a sufficient signal-to-noise ratio under the allowable X-ray dosage limit.From around mid-1990s,about a century after the discovery of X-ray,the substituting imaging method,the X-ray phase imaging,has been studied in order to overcome this difficulty.Various phase-sensitive methods have been developed to exploit the phase-contrast information in the X-ray regime.Among those X-ray phase contrast imaging(XPCI)techniques,the differential XPCI based on Talbot-Lau interferometer is one of the most promising approaches for medical and industrial applications since it works well with a broad energy spectrum and therefore can be combined with laboratory X-ray sources.Furthermore,X-ray grating interferometer(XGI)provides access to three complementary image modalities simultaneously:absorption,differential phase and small-angle scattering("dark-field")contrasts,significantly improving the diagnostic content.In this thesis,grating-based X-ray phase contrast imaging and related experimental techniques are studied,including:1.Non-interferometric grating-based phase contrast imaging system was constructed in Synchrotron Radiation Laboratory(NSRL).By developing a dynamic link library(DLL)using the Microsoft Visual Studio,the connection of the user operation software(developed by Lab VIEW)and the X-ray panel detector(PerkinElmer Inc.)was fulfilled.Thanks to the bridge DLL,the automatic data acquisition was completed.Moreover,we developed an auxiliary software for the system alignment.The Morie fringe formed by the projections of the two gratings is an important reference of the system alignment,while this software was developed to calculate the orientation and period of the Morie fringes fast and precisely.2.We present a novel body composition measurement method using the absorption and phase information obtained simultaneously from the XGI.Rather than requiring two projection data sets with different X-ray energy spectra in the widely applied dual-energy X-ray absorptiometry(DEXA),with the proposed method,both the areal densities of the bone and the surrounding soft tissue can be acquired utilizing one projection data set.A human body phantom was constructed to validate the proposed method,experimental results show that the body composition(the bone mineral density and the soft tissue areal density)can be calculated with an improved accuracy comparing to DEXA,especially for the soft tissue measurement.Since the proposed method can be easily implemented on current XGI setup,it has potential to be an alternate to DEXA for human body composition measurement,and meanwhile greatly extend the applications of the XGI.3.Two high-speed and low-dose data acquisition methods for XGI were proposed:continuous sliding window interlaced(CSWI)and sinusoidal phase modulation integrating-bucket(SPM-IB).By combining the sliding window technique,the projection number of the CSWI for the tomography reconstruction was substantially increased,improving the reconstructions and significantly reduced the image noise.Finally,trimodal radiography using sinusoidal phase modulating interferometry is studied.The signal retrieval algorithm using four integrating buckets is derived and demonstrated by numerical simulations.In the proposed method,the phase modulation is generated by shifting the grating following a sinusoidal curve while the signals are retrieved from the four frames obtained by integrating the time-varying intensity over the four quarters of the modulation period.Compared with the previously proposed method,this method is easier to implement due to relaxing requirements on the phase shifting device,meanwhile the high speed and continuous data averaging will greatly improve the performance of electronics,optical,and environmental noise.