Sense and non-sense of beam hardening correction in CT metrology

The polychromatic spectrum of X-ray beams causes beam hardening artifacts in reconstructed computed tomography (CT) models. This leads to unwanted grey value variations in CT models, thus hampering accurate material analysis and inspection. Therefore, beam hardening correction algorithms have been developed and improved since the early 1970s, which enhance the CT image quality by compensating for beam hardening effects. However, beam hardening correction often results in less contrast around the edge. In addition, experiments show an increased influence of surrounding material on the object dimensions after segmentation, hence increasing the measurement uncertainty. This paper presents the results of systematic investigations into the effect of beam hardening correction on the measurement accuracy and uncertainty for CT metrology applications.