A novel x-ray imaging technique based on coded apertures making phase contrast imaging feasible with conventional sources

Abstract

X-ray phase contrast imaging (XPCi) overcomes the main limitation of absorption-based x-ray imaging i.e. poor image contrast due to small absorption differences, and was proven capable to produce high contrast images of objects invisible to conventional methods. The problem so far was that XPCi was only feasible with synchrotron radiation sources (SR), which prevented any application of the technique outside the research domain. XPCi images can be produced outside SR only by means of microfocal sources, which result in dramatically increased exposure times. XPCi images with conventional sources were also obtained by means of a grating (or shearing) interferometer, but this still requires the source to be spatially coherent unless an absorption grid is placed in close contact with the source itself. By doing this, the output of the source is dramatically reduced, resulting in exposure times only marginally improved over those obtained with microfocal sources. We have developed a new technique, based on coded apertures, which overcomes all the above limitations and allows intense XPCi signals to be achieved with source sizes fully compatible with current state-of-the-art X-ray sources, without requiring any filtering/focusing/grating element to be placed in contact with the source thus suppressing its output. A pre-sample coded aperture system with a fill factor of 0.5 is used instead, which means that the increase in exposure time over conventional methods is only of a factor of 2. The technique was fully modelled and a proof-of-concept experiment carried out. The obtained results are in full agreement with the model, and demonstrate that image contrast increases comparable to those obtained with SR can be achieved with a focal spot of 100 micron. A larger scale imaging prototype aimed at homeland security is currently under development, and future applications aimed at medical, scientific and industrial imaging are currently being studied.