Calculation of Beam Hardening in Industrial X-ray Computed Tomography and its Correction using Filtration and Linearization Methods

Abstract

X-ray computed tomography is becoming an instrument for quality assurance as nondestructive testing for product inspection in industrial applications. However, the systematic error in the XCT image resulting from the physical processes of image reconstruction must be corrected. Beam hardening is one of the major artefacts that come due to an extensive range of photon energies in common x-ray sources in computed tomography instrument so-known polychromatic X-rays. The polychromatic can cause a nonlinear relationship between the attenuation and the thickness. As a result, the reconstructed image seems to have some darkness in the centre, which is considered a significant decreasing of the image quality. In this work the calculations of beam hardening and its correction using filtration and linearization methods were described. The calculations were done in four stages: the GEANT4 code was used for spectrum simulation; an optimum filter materials and thickness was chosen by a mean energy ratio method; the attenuation of aluminium material was numerically calculated using the basic polychromatic attenuation formulas, and the beam hardening was corrected using linearization and compared with the filtration method. The calculated polychromatic attenuations results of aluminium were found to be in good agreement with the existing literature. The linearization correction offers better beam hardening correction which gave a good linearity estimation without changing SNR when compared with the pre-filtration method.