A beam stop based correction procedure for high spatial frequency scatter in industrial cone-beam X-ray CT

In the energy range of industrial cone-beam CT (a 450 kV X-ray tube is used), the detector scatter (veiling glare) turned out to be the most important source of secondary radiation for a digital imaging system working in the indirect conversion mode. It has been shown that the detector scatter drives the shape of the total image scatter. As a consequence, the latter may be characterized by an important high spatial frequency content questioning the hypothesis, frequently invoked in the scatter correction techniques, of a slowly varying scatter. We propose a beam stop array (BSA) based method for the evaluation/subtraction of the image scatter. The technique has the potential of simultaneously manage all sources of scattering radiation. It can be used in the high spatial frequency scatter case at the condition of opportunely selecting the BSA effective sampling step. It has been shown that the BSA approach can be also successfully combined with a beam hardening correction scheme based on the linearisation method. The work we present is supported by experimental measurements performed with two test objects at two different beam qualities: (i) 200 kV + 2.5 mm of Cu and (ii) 400 kV + 4 mm of Pb and 1 mm of Cd. The detector scatter represents about 36% and 65% of the total white field image for the two investigated beam qualities, respectively.