X-ray computed tomography

Philip J. Withers, Charles Bouman, Simone Carmignato, Veerle Cnudde, David Grimaldi, Charlotte K. Hagen, Eric Maire, Marena Manley, Anton Du Plessis, Stuart R. Stock
2021 Nature Reviews Methods Primers  
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. This process is sometimes called a CT scan. A computed reconstruction algorithm is then used to create a stack of cross-sectional slices from these 2D
more » ... ns (radiographs) of the object. As illustrated in Box 1, this process provides a digital 3D greyscale representation (often referred to as a tomogram) of the internal structure of the object. This can be quantitatively analysed and virtually sliced in any direction or specific constituents can be digitally colour-coded, or rendered transparent, to visualize the 3D morphology. One of the main advantages of imaging by X-ray CT over other techniques is that it is non-destructive. This is critical when examining delicate samples that cannot easily be sectioned (for example, frozen ice cream 1 ), those samples that should not be damaged (for example, cultural artefacts 2 ) or where the structural integrity of an engineering component must be assured before it is deployed (such as a turbine blade). This, and the fact that modern CT systems can operate at X-ray doses that pose a relatively low risk to human health 3 , has led to its widespread use as a medical diagnostic tool. 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. ✉
doi:10.1038/s43586-021-00015-4 fatcat:zftzpghzf5h37ptmt7ynyxfwii