Modelling image formation and simplification of image aquisition for Talbot-Lau x-ray phase contrast CT

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Phase contrast imaging using the Talbot-Lau method delivers in addition to the usual absorption image the differential phase image and the darkfield image of an object. During the recent 10 years it has been proven that the differential phase image and the darkfield image contain valuable and complementary information to the absorption image. While the method is applicable at usual X-ray tubes, the polychromatic spectrum leads to artifacts in the images. An important and special aspect is related to the darkfield. The darkfield can be caused by granular structures like lung alveoli or micrometer-sized calzifications in breast tumors. This very interesting contribution can almost completely be overlayed by contributions from beam hardening or edges. Also the phase image and the absorption image may be affected by beam hardening. It should be noticed that the effect can be extreme for the darkfield: a darkfield image may exclusively contain structures due to beam hardening. This cannot occur in the phase and the absorption image. The Talbot-Lau method requires the acquisition of so-called phase stepping curves. This procedure can extend the acquisition time for CT imaging to an amount which may induce unwanted artifacts or even imply intolerable acquisition times. Within the applied project an iterative CT reconstruction strategy will be developed respectively further developed. The important ingredient is that the three images - absorption image, differential phase image and darkfield image - will not be reconstructed independently. Instead, by modeling the physics properties of the object the correlations in the three images will be taken into account in order to reduce noise and to eliminate artifacts. The applied iterative reconstruction primarily aims at the investigation of the correlations and is initially not intended to include other state-of-the-art measures for enhancing the image quality. Further, it will be investigated whether the phasestepping can be omitted for CT imaging thus reaching easier acquisition and shorter acquisition times. It might even be possible to waive the acquisition of the reference phasestepping curve.