Prog Med Phys.  2017 Sep;28(3):83-91. 10.14316/pmp.2017.28.3.83.

Numerical Modeling and Experiment for Single Grid-Based Phase-Contrast X-Ray Imaging

• Lim H
• Lee H
• Cho H
• Seo C
• Lee S
• Chae B

• KMID: 2393368
• DOI: http://doi.org/10.14316/pmp.2017.28.3.83

Abstract

In this work, we investigated the recently proposed phase-contrast x-ray imaging (PCXI) technique, the so-called single grid-based PCXI, which has great simplicity and minimal requirements on the setup alignment. It allows for imaging of smaller features and variations in the examined sample than conventional attenuation-based x-ray imaging with lower x-ray dose. We performed a systematic simulation using a simulation platform developed by us to investigate the image characteristics. We also performed a preliminary PCXI experiment using an established a table-top setup to demonstrate the performance of the simulation platform. The system consists of an x-ray tube (50 kV(p), 5 mAs), a focused-linear grid (200-lines/inch), and a flat-panel detector (48-µm pixel size). According to our results, the simulated contrast of phase images was much enhanced, compared to that of the absorption images. The scattering length scale estimated for a given simulation condition was about 117 nm. It was very similar, at least qualitatively, to the experimental contrast, which demonstrates the performance of the simulation platform. We also found that the level of the phase gradient of oriented structures strongly depended on the orientation of the structure relative to that of linear grids.

Keyword

Phase-contrast x-ray image; Simulation platform; X-ray grid; Image contrast

MeSH Terms

Absorption

Figure

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  Fig. 1. Schematic illustration of the single grid-based PCXI setup. Here the x-ray grid is placed midway between the x-ray source and the detector and an object to be examined is placed ahead of the grid.

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  Fig. 2. Schematic illustration of a geometry for the free-space propagation of x-rays. The wavefront ψ (x,y,z) in the detector plane that is calculated using the Huygens-Fresnel principle.

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  Fig. 3. The primary transmission, tgrid, of an ideal linear grid oriented in the vertical direction (i.e., in x). Here, d and D are the width of the lead strips and the distance between them, respectively, and P is the grid pitch.

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  Fig. 4. The simplified Fourier processing in the single grid-based PCXI to extract absorption image and differential phase image from the two raw images of the sample with a linear grid (fsg) and the bare grid (fg).

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  Fig. 5. (a) The 3D numerical chest phantom (478×258×434 voxels) in AP positioning (left) and LA (right) positioning and (b) the 3D Shepp-Logan phantom (400×400×400 voxels) used in the simulation.

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  Fig. 6. Table-top setup established for the experiment. It consists of an x-ray tube (100-mm focal spot size), a focused-linear grid (200-lines/inch strip density), and a CMOS-type flat-panel detector (14.5 cm×11.6 cm active area, 48-mm pixel size).

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  Fig. 7. The differential phase images of the chest phantom in AP positioning simulated with a vertical grid (top right) and a horizontal grid (bottom left) and their combined image (bottom right). The retrieved absorption image (top left) is also indicated as the reference.

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  Fig. 8. The differential phase images of the chest phantom in LA positioning simulated with a vertical grid (top right) and a horizontal grid (bottom left) and their combined image (bottom right). The retrieved absorption image (top left) is also indicated as the reference.

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  Fig. 9. The differential phase images of the Shepp-Logan phantom simulated with a vertical grid (top right) and a horizontal grid (bottom left) and their combined image (bottom right). The retrieved absorption image (top left) is also indicated as the reference.

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  Fig. 10. Intensity profiles measured along the line segments AB indicated in Fig. 9 for the differential phase image and the absorption image of the Shepp-Logan phantom.

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  Fig. 11. Complete sets of the PCXI results retrieved from a single raw image of (a) animal bone and (b) chicken wing with a 200-lines/inch vertical grid obtained at the given x-ray tube conditions of 50 kVp and 5 mAs.

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