When implementing differential phase-contrast imaging with current CT detectors the limited pixel size forces one to scan an analyser-grating in front of the detector to resolve the interference pattern. This simulation study compares the approach of using an analyser-grating and the approach of using a high-resolution detector to directly resolve the interference pattern by applying the non-prewhitening observer on dose-matched simulated CT scan reconstructions of the two approaches. A phantom with two concentric cylinders is used and 1000 CT scans are generated with the inner cylinder present and not present. The non-prewhitening observer is applied to the samples and the ROC curve is extracted, together with the results of a 2AFC test, the CNR, and the detectability. The high-resolution approach shows a 20% increase in the phase AUC compared to the grating-based approach, with a similar increase in the 2AFC test score. The image CNR of the phase shows an increase of 134%, with the detectability increasing by 138% when compared to the grating based approach. An ultra-high-resolution detector, capable of directly resolving the interference pattern of differential phase-contrast imaging could change medical imaging CT as we know it. The implementation in a clinical CT would be simpler, could lower cost, and increase the dose-efficiency due to the obviation of the G2-grating, and at the same time provide an additional two diagnostic signals.
We present the theory and implementation of a numerical model capable of simulating two-dimensional images for an x-ray
microscope using partially coherent illumination considerations. Partially coherent illumination is found in all x-ray
microscopes and particularly in the latest generation of our in-house compact soft x-ray microscope. This is due to an
introduced mismatch in numerical aperture of the condenser and objective zone plate, and will yield diffraction-like
artifacts in phase-shifting objects. The numerical model approximates the condenser zone plate as a secondary incoherent
source represented by individually coherent but mutually incoherent source emitters, each giving rise to a separate
image. A final image is obtained by adding up the image intensities of the individual contributions. The simulation has
been a useful tool for investigating the influence of coherence on images in both the mirror and zone plate condenser
arrangement of the in-house compact soft x-ray microscope. The latest development included in the program is the effect
of astigmatism and partial coherence, where the calculated results show good qualitative agreement with respect to the
microscope images.
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