Beam hardening in x-ray differential phase contrast computed tomography

Abstract

The effects of beam hardening have been an issue from the beginning of x-ray computed tomography. Polyenergetic beams are attenuated more at lower energies, resulting in the so-called hardening of the beam. Beam hardening artifacts in diagnostic CT images are a result of data inconsistency in the fundamental imaging equation in conventional absorption CT. In theory, in phase contrast imaging, the fundamental imaging equation is related only to a line integral of electron density, which is energy independent. However, due to unaccounted absorption in the imaging equation for phase contrast, beam hardening artifacts will make their way into phase contrast images. In this work, we use grating based differential phase contrast imaging, which uses a polyenergetic source, and extracts phase information from a set of intensity images. The energy dependence in the imaging equation for differential phase contrast imaging, coupled with the beam hardening present in the measured intensity data, results in beam hardening artifacts in the reconstructed results. We demonstrate the magnitude of the beam hardening effects in phase contrast reconstructions and compare it to standard absorption reconstructions.