Experimental Study On The Medical Application Of Hard X-Ray Phase Contrast Imaging Techniques

BackgroundConventional X-ray imaging has been widely used in the field of medicine. However, radiography with a conventional X-ray source has considerable limitations in imaging soft tissues, because conventional X-ray imaging methods generate contrast from differences in X-ray absorption, and the differences in X-ray absorption coefficients of the structures in soft tissues are quite small. Moreover, patient radiation doses delivered by conventional X-ray imaging has become a serious problem and threaten patient's health. Recently, research activity using X-ray phase information has been growing remarkably in the field of medicine. Phase-contrast imaging can offer a number of improvements over conventional radiography in clinical practice. What's more, phase-contrast imaging with synchrotron radiation can reveal the inner soft tissue such as tendons, ligaments, adipose tissue, cartilage, vessel and nerves without contrast agent, due to the sensitivity of this technique is more than 1000-fold higher than the conventional absorption-contrast X-ray method.Three techniques can be used for visualizing phase information: interferometric imaging, diffraction enhanced imaging (DEI) and in-line phase contrast imaging. However, the interferometric imaging need sophisticated X-ray optics and is employed almost exclusively at synchrotron light source facilities. Thus are felt to be less likely to be widely available in the near future. Therefore, our aim was to investigate the detailed appearance of images produced by the in-line phase contrast imaging and DEI in the organs of mouse. PartⅠIt is virtually impossible to observe blood vessels by conventional X-ray imaging techniques without using contrast agents. In addition, such X-ray systems are typically incapable of detecting vessels with diameters less than 200μm. Here we show that vessels as small as 30μm could be detected using in-line phase-contrast X-ray imaging without the use of contrast agents. Image quality was greatly improved by replacing resident blood with physiological saline. Furthermore, an entire branch of the portal vein from the main axial portal vein to the eighth generation of branching could be captured in a single phase-contrast image. Prior to our work, detection of 30μm diameter blood vessels could only be achieved using X-ray interferometer, which requires sophisticated x-ray optics. Our results thus demonstrate that in-line phase-contrast X-ray imaging using physiological saline as a contrast agent provides an alternative to the interferometric method that can be much more easily implemented and offers the advantage of a larger field of view. A possible application of this methodology is in animal tumor models, where it can be used to observe tumor angiogenesis and the treatment effects of antineoplastic agents. PartⅡNeovascularization is correlative with many processes of diseases, especially for tumor growth, invasion and metastasis. What is more, these tumor microvessels are very different from normal vessels in morphology. Therefore, observation of the morphologic distribution of microvessels is one of the key points for many researchers of the field. In this paper, we studied the mouse liver blood vessels under different DEI imaging conditions and assessed the quality of those images obtained at different positions of the monochromator - analyzer crystal rocking curve. Using diffraction enhanced imaging (DEI) method; we detected the microvessles with diameter of about 40μm in mouse liver. Moreover, the refraction image obtained from DEI images shows higher image contrast and exhibits potential use for medical applications. PartⅢPhase contrast imaging can easily demonstrate mouse liver microstructures with a diameter down to a few tens micron scale without contrast agent. However, it is still difficult to confirm all these microstructures are blood vessels because we cannot exclude bile ducts from these microstructures. Here we show that normal bile ducts cannot be demonstrated in phase contrast images. Mouse common bile duct was ligated to distend the bile ducts and the liver was then excised 40 days after ligation for imaging. Our results suggest that the pathological distended bile duct with diameter as small as 50μm can be demonstrated clearly without contrast agent. These dilated and tortuous bile duct are total different from blood vessels in morphous. What is more, the blood vessels and the bile ducts can be demonstrated at the same time without contrast agent. However, these structures cannot be discerned in control group. We also performed coronary artery imaging with diffraction enhanced imaging, and our results suggest that coronary artery can be demonstrated partially without contrast agent at present. Therefore, phase contrast imaging technique is a very promising tool in diagnostic bile ducts diseases and coronary artery diseases.