Abstract
X-ray computed tomography (CT) can reveal the internal details of objects in three dimensions non-destructively. In this Primer, we outline the basic principles of CT and describe the ways in which a CT scan can be acquired using X-ray tubes and synchrotron sources, including the different possible contrast modes that can be exploited. We explain the process of computationally reconstructing three-dimensional (3D) images from 2D radiographs and how to segment the 3D images for subsequent visualization and quantification. Whereas CT is widely used in medical and heavy industrial contexts at relatively low resolutions, here we focus on the application of higher resolution X-ray CT across science and engineering. We consider the application of X-ray CT to study subjects across the materials, metrology and manufacturing, engineering, food, biological, geological and palaeontological sciences. We examine how CT can be used to follow the structural evolution of materials in three dimensions in real time or in a time-lapse manner, for example to follow materials manufacturing or the in-service behaviour and degradation of manufactured components. Finally, we consider the potential for radiation damage and common sources of imaging artefacts, discuss reproducibility issues and consider future advances and opportunities.
Highlights
Radiographs Images formed by X-rays transmitted through an object, originally collected on a photographic plate but acquired digitally
X-ray computed tomography (CT) can provide unrivalled information about the internal structure of materials non-destructively from the metres down to the tens of nanometres length scales. It exploits the penetrating power of X-rays to obtain a series of two-dimensional (2D) radiographs of the object viewed from many different directions
We consider how computed reconstruction produces a 3D stack of slices from the 2D radiographs
Summary
Tomogram Originally a two-dimensional (2D) slice through an object reconstructed computationally from a sinogram. X-ray tubes are (relatively) simple, numerous and inexpensive devices that power laboratory CT scanners, whereas there are relatively few synchrotron facilities worldwide, each hosting dozens of experimental stations (including CT beamlines) tangential to the storage ring Their beams differ in terms of X-ray flux, source size and X-ray energy spectrum, as discussed below and in detail elsewhere[23]. In such cases, voxel sizes less than 50 nm can be used for specimens having dimensions ~50 μm or less[25]. Because the illumination provided by X-ray sources is far from uniform, and detectors show pixel to pixel variations in sensitivity, a projection must be acquired without the sample in the FoV to compensate nth detect urce position tor position First source a or position
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