X-ray diffraction tomography with limited projection information

Abstract

X-ray diffraction tomography (XDT) records the spatially-resolved X-ray diffraction profile of an extended object. Compared to conventional transmission-based tomography, XDT displays high intrinsic contrast among materials of similar electron density and improves the accuracy in material identification thanks to the molecular structural information carried by diffracted photons. However, due to the weak diffraction signal, a tomographic scan covering the entire object typically requires a synchrotron facility to make the acquisition time more manageable. Imaging applications in medical and industrial settings usually do not require the examination of the entire object. Therefore, a diffraction tomography modality covering only the region of interest (ROI) and subsequent image reconstruction techniques with truncated projections are highly desirable. Here we propose a table-top diffraction tomography system that can resolve the spatially-variant diffraction form factor from internal regions within extended samples. We demonstrate that the interior reconstruction maintains the material contrast while reducing the imaging time by 6 folds. The presented method could accelerate the acquisition of XDT and be applied in portable imaging applications with a reduced radiation dose.

Figure 1

Tomography system setup and reconstruction. (a) Illustration of the X-ray diffraction tomography (XDT) system. The sample is scanned across the pencil beam and rotated. A 2D diffraction pattern is captured at each sample position. (b) By averaging the 2D diffraction pattern in the azimuthal direction, the intensity profile along the radial direction, $r$, is extracted. (c) Each radial position along the diffraction profile forms a projection sinogram. For interior scan, the projection data does not contain translation outside the ROI. (d) Illustration of the sample composition. The red, dashed circle marks the ROI region. (e) Interior XDT reconstruction of the phantom from truncated projections. Different contrasts can be observed among water, ethanol and Smucker’s® soybean oil at momentum transfer $q$ = 0.10 ${Å}^{-1}$(e1), and 0.12 ${Å}^{\mathit{-}1}$ (e2). (f) Reconstructed form factor profile of water, ethanol and oil within ROI. The scale bar represents 5 mm.

Figure 2

Comparison between the reconstruction from full-FOV and interior XDT scan. (a) Reconstructed form factor from global and interior XDT scan compared with reference form factor of each material. (b) Material map of the global and interior scan. (c) Classifiers in boxed regions marked by the numbers in (b). The bin and error bar indicate the average and standard deviation of the probability within each region. (d) Conventional CT reconstruction. The scale bars represent 5 mm.

Figure 3

(a) Interior XDT reconstruction with fat and muscle region superimposed with a CT image of the sample. The inset shows the XDT contrast between fat and muscle at $q$ = 0.08 ${\mathrm{Å}}^{-1}$ and 0.16 ${\mathrm{Å}}^{-1}$. (b) Reconstructed diffraction form factor of fat and muscle inside the ham sample. (c) Simulated absorbed dose of interior XDT scan. (d) Simulated absorbed dose of global XDT scan. (e) The difference in absorbed dose distribution between the global and interior scan. The total dose administrated to the sample is reduced by 83%. The circle marks the interior region. The scale bar represents 5 mm.