Research On Image Acquisition System Of New Generation X-Ray Phase-contrast CT

Traditional absorption imaging is based on the difference of X-ray absorption cross section of different materials.However,the absorption cross section of different light elements is very close and very small,so the quality of X-ray absorption imaging for sample composed of light elements is poor.Compared with absorption imaging technology,X-ray phase contrast imaging technology can provide higher imaging contrast for soft tissue samples composed of light elements.After decades of development,a variety of phase contrast imaging methods have emerged,but these methods are demanding on the coherence and high luminance of X-ray,which means that few source can meet the requirements except for the synchrotron radiation and micro focus X-ray generator.In 2006,Talbot-Lau phase contrast imaging method based on conventional X-tube light source was proposed,but its application in the field of high-energy imaging was limited because of the requirement of small grating period.To solve this problem,the phase contrast CT imaging method based on geometric projection has been proposed.The grating period of geometric projection method does not need to be very small,so it can be used for high-energy imaging.In order to take advantage of the great advantages of phase contrast imaging in medical imaging and extend X-ray phase contrast imaging technology to clinical application,a new generation of three-dimensional phase contrast human CT based on geometric projection has been proposed.This paper mainly analyses the physical requirements of the new generation X-ray phase contrast CT,and designs an image acquisition system.The high voltage of the new generation phase contrast CT tube is set at 80KV.Its designed field of view is 666mm*24mm,which is the largest among these phase contrast equipments at present.Aiming at the technical characteristics of the new generation of phase contrast CT,this paper studies the image acquisition system.Ceramic scintillator array detectors with high light yield and detection efficiency are selected in this paper.According to the number of channels and the requirement of high resolution,an electronic readout scheme with high density and integration is designed.In order to realize high-speed and reliable transmission of image data between stator and rotor,a data transmission scheme is designed in this paper.The data transmission link adopts Xilinx GTX transceiver,SFP optical module and optical fiber slip-ring coupling mode.The data protocol uses Aurora 8B10B.In order to control the error code,CRC32 check and error code retransmit are adopted.Finally,a series of electronic tests and contrast imaging experiments are carried out on the phase contrast CT test platform.The test results show that the effective resolution of the system can reach 15.6 bit.The image acquisition system has a good linear performance and background stability and the signal-to-noise ratio performance can keep consistence with the commercial detector board.In two-dimensional and three-dimensional phase contrast imaging experiments,the image acquisition system can distinguish water from polyethylene plastic rods.The main innovations of this paper are as follows:(1)An image acquisition system is designed according to the characteristics of high energy and large field of view of the new generation X-ray phase contrast CT based on geometric projection.This is the first time in China to develop a high-energy,large field of view phase contrast CT image acquisition system.(2)Readout electronics with high density and large dynamic range was designed for ceramic scintillator array detector.The signal readout of 384 channels is realized in the size of 1.8cm*22cm PCB board.The test results show that the signal-to-noise ratio can keep consistence with commercial detector board MDBB-ST16_S.(3)Using the new technology of optical fiber data transmission based on fiber slip ring,the stable and reliable data reading between stator and rotor is realized.