RESUMEN
X-ray phase-contrast (XPCi) imaging methods are an emerging medical imaging approach that provide significantly better soft tissue contrast and could function as a viable extension to conventional X-ray, CT, and even some MRI. Absorption gratings play a central role in grating-based XPCi systems, especially because they enable the acquisition of three images in a single exposure: transmission, refraction, and dark-field. An impediment to commercial development and adoption of XPCi imaging systems is the lack of large area, high aspect ratio absorption gratings. Grating technology development, primarily due to technological limitations, has lagged system development and today prevents the scaling up of XPCi system into a footprint and price point acceptable to the medical market. In this work, we report on a self-aligned multi-layer grating fabrication process that can enable large-area X-ray absorption gratings with micron-scale feature sizes. We leverage large-area fabrication techniques commonly employed by the thin-film transistor (TFT) display industry. Conventional ITO-on-glass substrates are used with a patterned film of Cr/Au/Cr that serves as a self-aligned lithography mask for backside exposure. Commonly available SU-8 photoresist is patterned using the backside exposure mask followed by an electroplating step to fill the gaps in the SU-8 with X-ray attenuating material. Consequently, the electroplated patterned material acts as a self-aligned photomask for subsequent SU-8 layer patterning and so forth. The repeatability of the reported process makes it suitable for achieving higher aspect ratio structures and is advantageous over previously reported X-ray LIGA approaches. A prototype three-layer grating, with a thickness of around [Formula: see text], having a visibility of 0.28 at [Formula: see text] with a [Formula: see text] active area was fabricated on a 4-inch glass substrate and demonstrated by modifying a commercially available 3D propagation-based XPCi Microscope. The scalable and cost-effective approach to build larger area X-ray gratings reported in this work can help expedite the commercial development and adoption of previously reported Talbot-Lau, speckle-tracking, as well as coded-aperture XPCi systems for large-area clinical and industrial applications.
RESUMEN
In this work, we investigate the potential of employing a direct conversion integration mode X-ray detector with micron-scale pixels in two different X-ray phase-contrast imaging (XPCi) configurations, propagation-based (PB) and edge illumination (EI). Both PB-XPCi and EI-XPCi implementations are evaluated through a wave optics model-numerically simulated in MATLAB-and are compared based on their contrast, edge-enhancement, visibility, and dose efficiency characteristics. The EI-XPCi configuration, in general, demonstrates higher performance compared to PB-XPCi, considering a setup with the same X-ray source and detector. However, absorption masks quality (thickness of X-ray absorption material) and environmental vibration effect are two potential challenges for EI-XPCi employing a detector with micron-scale pixels. Simulation results confirm that the behavior of an EI-XPCi system employing a high-resolution detector is susceptible to its absorption masks thickness and misalignment. This work demonstrates the potential and feasibility of employing a high-resolution direct conversion detector for phase-contrast imaging applications where higher dose efficiency, higher contrast images, and a more compact imaging system are of interest.