Phase-contrast virtual chest radiography.

Respiratory X-ray imaging enhanced by phase contrast has shown improved airway visualization in animal models. Limitations in current X-ray technology have nevertheless hindered clinical translation, leaving the potential clinical impact an open question. Here, we explore phase-contrast chest radiography in a realistic in silico framework. Specifically, we use preprocessed virtual patients to generate in silico chest radiographs by Fresnel-diffraction simulations of X-ray wave propagation. Following a reader study conducted with clinical radiologists, we predict that phase-contrast edge enhancement will have a negligible impact on improving solitary pulmonary nodule detection (6 to 20 mm). However, edge enhancement of bronchial walls visualizes small airways (< 2 mm), which are invisible in conventional radiography. Our results show that phase-contrast chest radiography could play a future role in observing small-airway obstruction (e.g., relevant for asthma or early-stage chronic obstructive pulmonary disease), which cannot be directly visualized using current clinical methods, thereby motivating the experimental development needed for clinical translation. Finally, we discuss quantitative requirements on distances and X-ray source/detector specifications for clinical implementation of phase-contrast chest radiography.

X-ray phase contrast reveals soft tissue and shell growth lines in mollusks.

High-resolution 3D imaging of species with exoskeletons such as shell-bearing mollusks typically involves destructive steps. Nondestructive alternatives are desirable since samples can be rare and valuable, and destructive steps are time-consuming and may distort the tissue. Here, we show for the first time that propagation-based phase-contrast X-ray imaging can significantly increase contrast in mollusks with intact shells. By using the recently upgraded monochromator at the SPring-8 BL20B2 synchrotron beamline, we imaged six species of mollusks, showing that X-ray phase contrast enhances soft-tissue contrast. Features that are almost invisible in conventional attenuation-based micro-computed tomography (micro-CT) are clearly reproduced with phase-contrast imaging under the same scan conditions. Furthermore, this method can reveal features such as growth rings in the shell and differentiate between calcite and aragonite crystal forms. Phase-contrast imaging can thus serve as a compelling alternative when destructive methods are not an option.

In Silico Phase-Contrast X-Ray Imaging of Anthropomorphic Voxel-Based Phantoms.

Propagation-based phase-contrast X-ray imaging is an emerging technique that can improve dose efficiency in clinical imaging. In silico tools are key to understanding the fundamental imaging mechanisms and develop new applications. Here, due to the coherent nature of the phase-contrast effects, tools based on wave propagation (WP) are preferred over Monte Carlo (MC) based methods. WP simulations require very high wave-front sampling which typically limits simulations to small idealized objects. Virtual anthropomorphic voxel-based phantoms are typically provided with a resolution lower than imposed sampling requirements and, thus, cannot be directly translated for use in WP simulations. In the present paper we propose a general strategy to enable the use of these phantoms for WP simulations. The strategy is based on upsampling in the 3D domain followed by projection resulting in high-resolution maps of the projected thickness for each phantom material. These maps can then be efficiently used for simulations of Fresnel diffraction to generate in silico phase-contrast X-ray images. We demonstrate the strategy on an anthropomorphic breast phantom to simulate propagation-based phase-contrast mammography using a laboratory micro-focus X-ray source.