Minimizing the scatter contribution and spatial spread due to the absorption grating G2 in grating-based phase-contrast imaging

摘要

In previous research~1 it was shown that in grating-based phase-contrast imaging (GB-PCI) for low scatter objects, G2 is the dominant scattering source. This scatter is manifested in a different way compared to object scatter, as scattered photons that remain local to the interaction site may even increase object contrast, but reduce system visibility. In this work the magnitude and the spatial distribution of scattered photons from G2 are studied for different conditions using Monte Carlo simulations: (1) The effect of G2 orientation on the scatter-to-primary ratios (SPRs), (2) the impact of reducing the G2-to-detector distance (D) from 1.21 cm (current setting) to 0.5 cm on the spatial scatter distribution, and (3) the possibility to apply the G2 scatter probability to predict the scatter images from any primary object image. It was shown that flipping the G2 grating with its substrate away from the detector reduces the scatter-to-primary ratio by a factor 1.15. Furthermore, when D is 1.21 cm, 50% of the scattered photons fell within the first 18 pixels, while for D equal to 0.5 cm, 50% fell within the first 9 pixels, with however a slightly increased SPR. It was shown that convolution of these spatial distributions with the primary images of low scattering objects allows prediction of scatter images with a mean percentage deviation of 21% and 16% for D is 0.5 and 1.21 cm respectively. This work therefore illustrates that small optimization steps can have a notable impact on the magnitude and spatial distribution of scattered radiation at the level of the detector in GB-PCI. An approach to estimate scattered radiation images for objects that produce low levels of scattered radiation was presented.