X-ray phase contrast imaging using a grating interferometer

Abstract

In conventional x-ray imaging, contrast is obtained through the differences in the absorption cross section of the constituents of the object. The technique yields excellent results where highly absorbing structures, e.g., bones, are embedded in a matrix of relatively weakly absorbing material, e.g., the surrounding tissue of the human body. However, in those cases where different forms of tissue with similar absorption cross-sections are under investigation (e.g., mammography or angiography), the x-ray absorption contrast is relatively poor. Consequently, differentiating pathologic from non-pathologic tissue from an absorption radiograph obtained with a current hospital-based x-ray system still remains practically impossible for many tissue compositions.
To overcome these limitations, several methods to generate radiographic contrast from the phase shift of x-rays passing through the sample have been investigated in recent years.They can be classified into crystal interferometer methods, techniques using an analyzer, and free-space propagation methods. Although some of them yield excellent results for specific problems, none is very widely used. In particular, none of them has so far found medical diagnostics applications,which require a large field of view of many centimeters, the efficient use of broadband radiation as provided by laboratory X-ray generators and a reasonably compact setup.
As an alternative approach we have recently developed a grating based differential phase contrast (DPC) setup which can efficiently be used to retrieve quantitative phase images with polychromatic x-ray sources of low brilliance. Some of the recent results are reviewed in the following.