Phase contrast and coherent scatter imaging have the potential to improve the detection of materials of interest in x ray screening. While attenuation is dependent on atomic number, phase is highly dependent on electron density, and thus offers an additional discriminant. A major limitation of phase imaging has been the required spatial coherence of the xray illumination, which typically requires a small (10-50 μm) source or multiple images captured with precision gratings, both of which present challenges for high throughput image acquisition. An alternative approach uses a single coarse mesh. This significantly relaxes the source spot size requirement, improving acquisition times and allows near-real-time phase extraction using Fourier processing of the acquired images. Diffraction signatures provide a third approach which yields another set of information to identify materials. Specific angles characteristic of target materials are selected through broad slot apertures for rapid throughput. Depth information can be extracted from stereoscopic imaging using multiple slots. A system capable of simultaneous phase, coherent scatter, and absorption imaging was constructed. Discrimination of materials on the basis of both phase and coherent scatter signatures is demonstrated.
X-ray phase contrast can offer improved contrast in soft tissue imaging at clinical energies. To generate phase contrast in a clinical setting without the need for precisely aligned gratings and multiple exposures has traditionally required the use of specialized sources capable of producing x-ray spots on the order of 10 μm in diameter which necessarily require lengthy exposures due to the low intensity produced. We demonstrate results from two systems capable of overcoming this limitation. In the first, a polycapillary optic is employed to focus a typical clinical source to produce a small secondary source of the size required for phase contrast imaging. In the second, a grid of relatively large pitch is used along with Fourier processing to generate a phase contrast image using a large spot size source.
X–ray phase imaging utilizes a variety of techniques to render phase information as intensity contrast and these
intensity images can in some cases be processed to retrieve quantitative phase. A subset of these techniques
use free space propagation to generate phase contrast and phase can be recovered by inverting differential
equations governing propagation. Two techniques to generate quantitative phase reconstructions from a single
phase contrast image are described in detail, along with regularization techniques to reduce the influence of
noise. Lastly, a recently developed technique utilizing a binary–amplitude grid to enhance signal strength in
propagation–based techniques is described.
A recently developed technique for phase imaging using table top sources is to use multiple fine-pitch gratings.
However, the strict manufacturing tolerences and precise alignment required have limited the widespread adoption
of grating-based techniques. In this work, we employ a technique recently demonstrated by Bennett et al.<sup>1 </sup>that
ultilizes a single grid of much coarser pitch. Phase is extracted using Fourier processing on a single raw image taken
using a focused mammography grid. The effects on the final image of varying grid, object, and detector distances,
window widths, and of a variety of windowing functions, used to separate the harmonics, were investigated.
Contrast in conventional imaging of soft tissues is often limited due to the very similar attenuation of
tissues to be distinguished. Phase contrast techniques can enable discrimination of tissues with similar attenuation. A
major limitation to the widespread adoption of phase-contrast techniques is that for tabletop sources the required
degree of coherence generally requires a small (10 to 50 μm) source. In this work, a polycapillary optic was
employed to create a small virtual source from a large spot rotating anode. Phase contrast images obtained with two
optics and several pinholes have been analyzed and preliminary results obtained for quantitative phase