Quantitative imaging using high-energy X-ray phase-contrast CT with a 70 kVp polychromatic X-ray spectrum.

Imaging of large and dense objects with grating-based X-ray phase-contrast computed tomography requires high X-ray photon energy and large fields of view. It has become increasingly possible due to the improvements in the grating manufacturing processes. Using a high-energy X-ray phase-contrast CT setup with a large (10 cm in diameter) analyzer grating and operated at an acceleration tube voltage of 70 kVp, we investigate the complementarity of both attenuation and phase contrast modalities with materials of various atomic numbers (Z). We confirm experimentally that for low-Z materials, phase contrast yields no additional information content over attenuation images, yet it provides increased contrast-to-noise ratios (CNRs). The complementarity of both signals can be seen again with increasing Z of the materials and a more comprehensive material characterization is thus possible. Imaging of a part of a human cervical spine with intervertebral discs surrounded by bones and various soft tissue types showcases the benefit of high-energy X-ray phase-contrast system. Phase-contrast reconstruction reveals the internal structure of the discs and makes the boundary between the disc annulus and nucleus pulposus visible. Despite the fact that it still remains challenging to develop a high-energy grating interferometer with a broad polychromatic source with satisfactory optical performance, improved image quality for phase contrast as compared to attenuation contrast can be obtained and new exciting applications foreseen.

Connecting microfluidic chips using a chemically inert, reversible, multichannel chip-to-world-interface.

In this paper we present a reusable, chemically inert, multichannel Chip-to-World-Interface (CWI). The concept of this interface is based on a force fit connection similar to the hollow screw connectors known from high-performance liquid chromatography (HPLC) instruments. It allows contamination free connection of up to 100 thermoplastic tubes to microfluidic chips made from various materials e.g., epoxy polymers, glass and polydimethylsiloxane (PDMS). The spacing of the tubes is fixed whereas the outer dimensions of the CWI can be adapted to the microfluidic chip it should be used with. We demonstrate that such a CWI with 100 tubes is pressure-tight up to (at least) 630 kPa (6.3 bar) pressure and the connection easily sustains flow rates above 4 ml min(-1). The presented CWI is designed such that the fluid probed in the microfluidic chip is in direct contact only with the tube material and the material from which the microfluidic chip is made. This not only enables fluid transport without dead volume, it also ensures that CWI itself will not be contaminated or contaminate the samples being probed. Using polytetrafluoroethylene (PTFE, Teflon®) tubing we demonstrate that the CWI can even be used with harsh organic solvents such as dichloromethane or dimethylformamide during continuous solvent probing over several hours without damage to the CWI or leakage. This CWI therefore effectively allows using almost all types of organic solvents in microfluidic applications.