X-ray phase contrast tomography by tracking near field speckle

Abstract

X-ray imaging techniques that capture variations in the x-ray phase can yield higher contrast images with lower x-ray dose than is possible with conventional absorption radiography. However, the extraction of phase information is often more difficult than the extraction of absorption information and requires a more sophisticated experimental arrangement. We here report a method for three-dimensional (3D) X-ray phase contrast computed tomography (CT) which gives quantitative volumetric information on the real part of the refractive index. The method is based on the recently developed X-ray speckle tracking technique in which the displacement of near field speckle is tracked using a digital image correlation algorithm. In addition to differential phase contrast projection images, the method allows the dark-field images to be simultaneously extracted. After reconstruction, compared to conventional absorption CT images, the 3D phase CT images show greatly enhanced contrast. This new imaging method has advantages compared to other X-ray imaging methods in simplicity of experimental arrangement, speed of measurement and relative insensitivity to beam movements. These features make the technique an attractive candidate for material imaging such as in-vivo imaging of biological systems containing soft tissue.

State of the Art of X-ray Speckle-Based Phase-Contrast and Dark-Field Imaging

“…In a first report, the phase and transmission tomograms of a human artery obtained with the single-shot XST mode (see Section 3.1) were shown [89]. The superior sensitivity to density differences of the phase signal over the transmission signal, here between the artery lumen and walls, was observed in a qualitative way; see Figure 10I in Section 7.2.…”

“…It has been demonstrated that microfocus laboratory sources provide sufficient spatial coherence for successful implementation of X-ray speckle-based imaging [85]. Alternatively, it has been proposed to use a random pattern created by absorption rather than interference effects to track the beam wavefront under conditions of low spatial coherence [89,136]; see Section 5.…”

“…It has also been proposed that alternatively the reduction of the cross-correlation peak value can be taken as a measure for the dark-field signal [89]; see Section 4.…”

“…In another implementation, Wang et al used an approach based on the reduction of the peak value of the local cross-correlation coefficient between reference and sample signals to calculate the dark-field image for the XST single-shot analysis [89]. The dark-field signal is here defined as D = 1 − γ max , where γ max is the maximum (peak) value of the cross-correlation coefficient, which is obtained for each pixel from the zero-normalised cross-correlation of the sample and reference subset windows.…”

Simulations of multi-contrast x-ray imaging using near-field speckles

“…Among the several techniques developed in the last years, a method based on tracking of near-field speckles has several advantages [4][5][6][7][8]. The setup, data acquisition and analysis procedures are relatively simple, it provides multicontrast signals in different directions, and it works well not only at synchrotron facilities, but also at polychromatic laboratory sources [9,10].…”