A simulation tool for X-ray phase-contrast micro-CT featuring a small-pixel photon-counting detector

X-ray micro-CT (µCT) is an important tool for high-resolution, non-destructive inspection of samples with numerous applications ranging from preclinical imaging to materials science. µCT imaging capabilities can be expanded through the use of small-pixel (<100 µm) photon-counting detectors (PCDs) which increase image contrast, reduce image noise, and provide additional insights into material composition through the collected spectral information. Along the same lines, phase-contrast X-ray imaging is increasingly being adopted in laboratory µCT imaging setups to improve the visualization of low-attenuation contrast samples. Along with these technological improvements comes the need for improved modeling and simulation. However, no laboratory µCT simulation tool currently exists that includes a small-pixel PCD. PEPIsim addresses this need, providing a simulation resource that produces photon-counting, spectral, and phase-contrast µCT reconstructions, accurately modelling the response of the small-pixel PCD in addition to incorporating phase-contrast effects. PEPIsim has been benchmarked against experimental images of a custom plastic phantom acquired with a µCT setup featuring a PCD and a micro-focus X-ray tube. Results showed that the simulation reproduces the system spectral response (average NMRSE of 2.7%) across a wide range of tube voltages (45- 100 kVp). Moreover, good accuracy in terms of measured X-ray attenuation (average relative error (RE) of 1.5%) and SNR (average RE of 6.5%) has been found. Similarly, after phase-retrieval, the simulated images’ SNR is found to be in agreement with experimental images (average RE of 5.5%). Finally, the simulation can also reproduce the fringe visibility due to the edge-enhancement effect (average RE of 5.2%) across a range of magnifications (from 1.3 to 3.7) and source to detector distances (from 40 to 133 cm). Due to its modular structure, PEPIsim can be adapted to any experimental µCT imaging setup, provided that accurate detector and X-ray tube models exist.