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Experiment Study of the Phase-Contrast Technique in Medical Imaging

Author: PengYiFeng
Tutor: ChenShaoLiang;XuHongJie;ZhangGuiLin;ShiHongCheng;HeZuo
School: Fudan University
Course: Medical Imaging and Nuclear Medicine
Keywords: Phase contrast technology Synchrotron radiation (SR) In-line holography imaging Coronary artery imaging Diffraction enhanced imaging (DEI) Monochromatic light
CLC: R814.4
Type: PhD thesis
Year: 2006
Downloads: 120
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Abstract


Objective Fingding out the difference between the abnormal and the normal is the diagnosis basement of medical imaging, over one hundred years since Rotgen discovered the X ray in 1895 X-rays has been the mainly imaging tackle for more than one century. By now, however, absorption difference has been almost the unique mechanism to differentiate the normal and abnormal tissue, even the normal tissue itself in imaging medical. For the tissue in which the density difference is large it may be a good technique, however, it may be not available for the tissue in which the density difference is weak, especially in soft tissue which is mostly transaparent to conventional X ray. the phase change much more sensitive than the absorption, the phase contrast thchnique can separate the all kinds of effectives(such as scatters、refraction absorption, et al) which comes from the interaction between the X-rays and objects, transforms phase change into intensity change and then image, It is necessary that the light source is partly spatial coherence, Synchrotron Radiation (SR) is such an excellent light source as high collimation、brightness and coherence, especially for soft tissue imaging. On the experiments including the phase-contrast imaging and the coronary angiography, the study aim to evaluate the latent value and analyze the difficulty in medical imaging with the Synchrotron Radiation (SR) in order to serve the deeply application of the advanced Synchrotron Radiation (SR) in clinical medical in the future.Material and Methods the experiments were performed in the 4W1A of the BSRF (Beijing synchrotron radiation facility in china), the samples were soaked in 4% formalin solution, before scanning they were incised equally by lcm size and 0.3-0.4cm thickness, all the samples were located on the shelf and imaged respectivly, the imaging methods contained "in-line" phase contrast imaging and diffraction-enhanced imaging (DEI). in the "in-line" phase contrastprocessing, the sample shelf moved along the light beam way, the influence of the effective distance between samples and the imaging facility on the imaging results was analyzed; the diffraction-enhanced imaging (DEI)was the important content in the study, during the diffraction-enhanced imaging (DEI)processing, at first, the analyzed crystal rocking curve(denoting the relation the reflection ratio and the rocking angle) was scanned , then the different location in rocking curve were selected to scan including mainly the peak location, the half- maximum location and the bottom location on the high angle and the low angle side. The image were analyzed and compared with corresponding conventional examination and pathology result, The image resolution was calculated by micro-magnify method. At last two methods including the diffraction-enhanced imaging (DEI) and monochrome imaging were used to image the mouses’ coronary vessels, and the resolution and contrast differences were compared. For the reasons that the requirement of the X-ray interferometry imaging is that the crystal must be high precise and stable, and at that time the condition was limited in the BSRF (Beijing Synchrotron Radiation facility), we gave up the the X-ray interferometry imaging experiment. Results good contrast was obtained in the "in-line" phase contrast imaging with resolution reach to level of micron, the effective distance between samples with imaging facility has good correlation with image contrast. In the DEI experiment there were different rocking curve in different tissues and the difference wasn’t only from tissue density; Besides the base information was approximately similar to the conventional, the diffraction enhanced imaging (DEI) provided additional microstructure information and the resolution reached to level of micron. The image at the peak location was similar with the absorption image (in fact the image was more clear for it was free of scatter, so the peak location was also named as extinct contrast image).The image at the half-maximum location was absolutely different image with greater clarity thanthe conventional image; the contrast was analyzed at other locations in the rocking curve. As the imaging principle of DEI, the images at the half-maximum location on the rocking curve were calculated to make the apparent absorption image and the refraction image. On the coronary artery imaging with DEI, the heart and vessels images were obtained without any contrast media, the image contrast was still good; the monochrome imaging technique, however, can display dynamic image of the heart and coronary artery and the relations with in the cardi(?) cycle, there weren’ t significant difference in coronary vessels diameter measurement results between the two imaging methods, however, because the specific imaging mechanism, there is less radiation dose in imaging with the DEI(Diffraction enhanced imaging) than the the monochrome imaging technique in that indicated the DEI (Diffraction enhanced imaging) may well play important role in development of SR imaging in the future for its relatively security. Conclusion unlike the conventional X ray imaging, the phase-contrast imaging can well display the inner microstructure, providing many additional information and the resolution is very high. on the phase-contrast mechnism many clinical medical application studies can be performed, especially the weak absorption tissue imaging. the mainly requirement to the light source is partly spatial coherence, the synchrotron radiation is justly as such light source, it is high brightness、high collimation、time- pulse additionally, so besides phase contrast imaging, it adapts to coronary artery imaging . the weakness for the synchrotron radiation in medical application is that the light source facility is too bulky to popular in clinical medical for its incovenience, at present the application is limited on foundation pathoiogy、medical biology chemistry and the study and development of new imaging and medical treatment technology. In additionally, the BSRF (Beijing Synchrotron Radiation facility) is the first generation side facility in which the index can’t come to the optimization, so it couldn’t compare with the dedicated facility whichindicates that the research latent is large; on the oilier hand, the emission from the synchrotron radiation is sector-linear light source, although it is suit to monochromator, can’t meet the area requirement for imaging. so it should be enlarged enough to adapted to the medical imaging diagnosis (the size of light source area should be about 15centimeters for normal human being check requirement).

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