X-ray Phase-Contrast Radiography and Tomography with a Multiaperture Analyzer

We present a multiaperture analyzer setup for performing x-ray phase contrast imaging in planar and three-dimensional modalities. The method is based on strongly structuring the x-ray beam with an amplitude modulator, before it reaches the sample, and on a multiaperture analyzing element before detection. A multislice representation of the sample is used to establish a quantitative relation between projection images and the corresponding three-dimensional distributions, leading to successful tomographic reconstruction. Sample absorption, phase, and scattering are retrieved from the measurement of five intensity projections. The method is tested on custom-built phantoms with synchrotron radiation: sample absorption and phase can be reliably retrieved also in combination with strong scatterers, simultaneously attaining high sensitivity and dynamic range.

Figure 1

Experimental setup (a): monochromatic synchrotron radiation is shaped to a narrow beam by a simple aperture before the sample. It is then analyzed by a set of apertures before detection. 2D images are built by scanning the sample along $y$. Simulated (solid line) and experimental (circles) illumination functions (b): an approximate Si (111) rocking curve is also plotted (dashed line) for comparison (20 keV).

Figure 2

Phantom consisting of a perspex cylinder and a paper step wedge: transmission (a) and (d), phase (b) and (e), and dark field (c) and (f). The images at high resolution, in panels (a)–(c), can be compared to the images at low resolution, shown in panels (d)–(f). The profiles reporting the dark-field signal (g) and the phase shift (h) measured along the lines highlighted in the panels (c),(f) and (b),(e), respectively, show that the spatial resolution does not affect accuracy. A very good match betweeen theoretically expected and experimentally measured profiles can be observed for the phase image.

Figure 3

Quantitative profiles of transmission (a) and dark field (b) extracted from images of the melamine sample. The dark-field signal ${\sigma }^2$ is directly proportional to the sample thickness, as expected. The two insets show CT slices absorption (a) and dark-field (b) images of the microspheres embedded in acrylic.

Figure 4

Absorption and dark-field CT of a scaffold in false colors (absorption: magenta and dark field: cyan), blended. It can be seen how the two different contrast channels provide a complementary representation of this complex sample.