X-ray beam shaping for a custom-made X-ray scattering system.

Coherent X-ray scattering is the basis of phase-contrast imaging (PCI). PCI departs from traditional planar and tomographic diagnostic X-ray imaging contrast relying on differences of the linear attenuation coefficient among human tissues. PCI exploits differences of the coherent scattering form factor among tissues for momentum transfer argument (x) values between 0 and 10 nm^-1 (i.e., forward X-ray scattering). An ad-hoc X-ray scattering system was built on a platform designed for X-ray fluorescence experiments and consisted of a rotating arm supporting a silicon X-ray detector mounted in the beam’s path from an integrated X-ray tube and polycapillary lens unit. Limited space allowed only forward scattering angles up to 28 degrees and X-ray beam had an angular divergence of ~4 degrees (FWHM/2), hindering measurements at low scattering angles (<10 degrees). Thus, for 11.28 keV tungsten X-rays, measurable x ranged from 0.79 to 2.2 nm^-1. A custom-made collimator made of two steel blades separated by an adjustable gap (<50 µm) halved the beam’s angular divergence. Misalignment, however, shifted the average incidence angle by ~7.4 degrees, giving two x ranges: 0 to 0.4 nm^-1 and 0.87 to 2.2 nm^-1.