Double-exposure method for speckle-tracking x-ray phase-contrast microtomography

X-ray phase-contrast microtomography based on speckle tracking is an attractive method for non-destructive three-dimensional imaging owing to its simple setup and ability to yield absorption, refractive, and scattering images simultaneously. However, the edge-enhancement effect usually results in image artifacts or inaccurate phase retrieval, limiting the extensive application of this method in biomedical research and for low-Z materials. In this paper, a double-exposure method is introduced to solve this problem efficiently and accurately. Pure phase samples with various microstructures and densities and a biological sample with a distinct edge-enhancement effect were used to verify the effectiveness of the developed method. In an experiment performed using a polymer phantom with an evenly distributed density, 17 irregularly shaped particles with diameters ranging from 15 to 25 mu m were successfully reconstructed with the effective elimination of the edge-enhancement effect. The results obtained for a sample composed of different polymer materials demonstrated that, in contrast with the traditional speckle-tracking method, the present method is able to discriminate materials with similar x-ray attenuations. Finally, experiments were performed using a dehydrated fish, which entail typical edge enhancement and a complex microstructure; notably, it was verified that the fine structure of the fish, including its fins and intestines, was reconstructed completely using the proposed method, whereas the standard speckle-tracking method was ineffective. In conclusion, the developed double-exposure method can serve as an efficient and accurate technique for the x-ray phase-contrast microtomography of samples comprising low-Z materials and complicated microstructures.