Medical differential phase contrast x-ray imaging (DPCI) promises improvedsoft-tissue contrast at lower x-ray dose. The dose strongly depends on both theangular sensitivity and on the visibility of a grating-based Talbot-Lauinterferometer. Using a conventional x-ray tube, a high sensitivity and a highvisibility are somewhat contradicting goals: To increase sensitivity, thegrating period has to be reduced and/or the grating distance increased.Technically, this means using a higher Talbot order (3rd or 5th one instead offirst one). This however reduces the visibility somewhat, because only asmaller part of the tube spectrum will get used. This work proposes to relaxthis problem by changing the phase grating geometry. This allows to doublesensitivity (i.e., double the Talbot order) without reducing the visibility.One proposed grating geometry is an older binary one (75% of a period$\pi$-shifting), but applied in a novel way. The second proposed geometry is anovel one, requiring three height levels for polychromatic correction. Theadvantage is quantified by a simulation of the resulting interference patterns.Visibilities for the common $\pi$-shifting gratings are compared with theproposed alternative geometries. This is done depending on photon energy andopening ratio of the coherence grating G0. It shows that despite of doubledsensitivity of the proposed gratings, the overall visibility might even improvea little.
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