Phase contrast imaging takes advantage of the fact that different materials have different refractive indices. This produces a phase shift in the X-rays passing through the sample. By placing the imaging detector at a specific distance from the sample, interference between waves can be used to enhance contrast in the image.
Whilst phase contrast imaging is possible using laboratory techniques, the highly coherent X-rays beams make it possible to gather data with much simpler instrumentation. In addition, it is possible to achieve higher spatial resolution, and to carry out phase contrast tomography, where three dimensional images are created from two dimensional scans.
Phase contrast imaging enables the examination of crack growth and fatigue in materials under stress, which is of particular importance in the aerospace and engineering industries. It is particularly useful for enhancing the contrast of surfaces and interfaces in samples, which would not be visible using absorption contrast.
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