Diffraction-enhanced Imaging of Human Tooth Using Highly Spatial Coherent Parametric X-ray Generated by a Small LINAC System

Abstract

Fine histological structures of human tooth were examined through diffractionenhanced imaging using highly spatial coherent parametric Xray (PXR) generated by a smallscale electron accelerator at the Laboratory for Electron Beam Research and Application (LEBRA) , Nihon University. LEBRA -PXR is used as an electron linear accelerator (LINAC)based jointuse Xray source to facilitate advanced Xray imaging experiments such as phasecontrast imaging with diffractionenhanced imaging (DEI) , which has been considered difficult to perform outside a synchrotron radiation facility.In this study, several microscopicorder structures of the enamel and dentin were identified through ultrasmallangle Xray scattering (USAXS) imaging using DEI, although these structures were not visualized through refractionangle image of DEI except for the contour lines of the tooth and enameldentin junction. In USAXS images, local variations in dentin structures, particularly in the presence of microsized tubules, such as dentin tubules, were visualized differently depending on the sample orientation. The specimen's appearance when the tooth axis was parallel to the floor differed from that when it was vertical to the floor. Such directional dependence is unique to LEB-RA -PXR, which is sensitive to horizontal but not vertical refraction and scattering. The orientation of anisotropic sample structures was confirmed by changing the sample orientation. PXR generated in a small LINAC system was sufficient to observe tooth histological structures. Technical improvements should lead to clearer and more detailed images of innerteeth structures, and the possibility of threedimensional construction using phase contrast imaging would help in detailed elucidation of tooth development, growth, and calcification mechanism.