Evaluation of two phase contrast techniques:: Diffraction enhanced imaging and propagation

Two X-ray phase-contrast imaging techniques are compared in a quantitative way for future mammographic applications: Diffraction Enhanced Imaging (DEI) and Propagation. The first uses an analyzer crystal after the sample acting as an angular filter for X-rays refracted by the sample. The latter simply uses the propagation (Fresnel diffraction) of the monochromatic and partially coherent X-ray beam over large distances. Experiments to compare both modalities have been performed at the Topography Beamline of the European Synchrotron Radiation Facility. The respective set-ups and experimental parameters are described in detail. Depending on the object properties, the two techniques present a difference in area contrast and edge visibility. DEI shows an enhancement of area contrast for positions of the crystal corresponding to the tails of its rocking curve (RC) and a similar increase but inverted is also visible at the peak of its RC. At the tails, the contrast is mainly produced by ultra small angle scattering, at the peak, it is due to absorption and scatter rejection by the analyzer. At the flanks, it may disappear when attenuation and scattering effects compensate each other. However, an enhancement of the object edges is clearly noticeable, which mainly corresponds to the refracted part. Propagation reveals an improvement of the edge visibility with the distance and shows negligible area contrast for non-absorbing, large structures.