X-Ray Tomography

X-ray absorption tomography is a non-destructive technique for reconstructing "cross-sectional" images of a three-dimensional object.

Its principle is based on the multidirectional analysis of the interaction of an X-ray beam with matter, by recording with detectors the radiation transmitted after passing through an object.

The data acquired during the measurement process (the duration of which varies from a fraction of a second to several hours, depending on the installation) is collected in multiple orientations, the number and spacing of which depend on the type of device and the resolution level.

Using this data, a digital image is calculated and mathematically reconstructed in levels of gray or color, each of which translates point by point the local attenuation coefficient of the incident beam. After calibration, this can be translated into a density scale.

X-ray tomography provides access to the heart of matter, allowing us to appreciate variations in radiological absorption and differences in composition.

It can also be used to pinpoint any heterogeneities, singularities, voids or inclusions present in an object, and to check the assembly and positioning of complex mechanical assemblies.

Finally, when acquisition times are compatible with the speed of certain physical phenomena, tomography can be used for dynamic measurements, for example, to monitor the evolution of a material under stress.

Developed for the medical field, this promising technique has adapted its parameters to the industrial field, where all sectors can benefit from its possibilities, whether in aeronautics, the automotive sector, foundries, the mining or oil industries, or the agri-food sector.

X-ray tomography is used for production, prototyping and process development.

This article presents the mathematical and physical principles involved in the tomographic technique. The author stresses the important parameters for acquiring a quality image, and underlines the pitfalls to be avoided, as well as the solutions to be implemented to prevent harmful artifacts on the reconstruction, which are the cause of erroneous diagnoses in non-destructive testing. It also presents the reasons for the undeniable development of this technique, which, for economic contingencies of lower cost, precisely analyzes the defects present within the material and their possible evolution to make them acceptable in many cases, moving the technique from a "zero defect" industrial strategy to a "permissible defect" strategy. Finally, thanks to advances in detectors and computers, tomography has found a new field of experimentation in high and...