Multi-material gap measurements using dual-energy computed tomography

X-ray computed tomography is a highly versatile investigation method with applications in a wide range of areas. One of the areas where the technique has seen an increased usage, and an increased interest from industry, is in dimensional metrology. X-ray computed tomography enables the measurement of features and dimensions that are difficult to inspect using other methods. However, there are issues with the method when it comes to measurements of objects that consist of several materials. In particular, it is difficult to obtain accurate computed tomography results for all materials when the attenuation of materials differs significantly. The aim of this work was to measure small air gaps between different materials using dual-energy X-ray computed tomography. The dual-energy method employed in this work uses two energy spectra and fuses the data in the projections space using non-linear fusion. The results from this study show that the dual-energy method used in this work was able to capture more measurements than regular absorption computed tomography in the case of specimens with highly different attenuation, enabling, in particular, the measurement of smaller gaps. The contrast-to-noise ratio was also increased significantly with the use of dual-energy.