Phase-Contrast X-Ray Imaging of Complex Objects
Time: Fri 2021-05-28 13.00
Subject area: Physics Biological and Biomedical Physics
Doctoral student: Ilian Häggmark , Biomedicinsk fysik och röntgenfysik
Opponent: Professor Henning Friis Poulsen, Department of Physics, Technical University of Denmark, Copenhagen , Denmark
Supervisor: Professor Hans Hertz, Biomedicinsk fysik och röntgenfysik; Universitetslektor Anna Burvall, Biomedicinsk fysik och röntgenfysik
X-ray imaging is a group of techniques using electromagnetic radiation of high energy. The ability to quickly visualize internal structures in thick opaque objects has made it an indispensable tool in research, medicine, and industry. Contrast is generally achieved by differential absorption, however, this mechanism has a strong dependence on atomic number. This results in low contrast within materials consisting of mainly elements of low atomic number, such as hydrogen, carbon and oxygen, e.g., soft organic matter. The problem with low contrast is further complicated by limitations in radiation dose. To improve contrast the phase shift of the X-rays can be measured without increasing the dose.
This Thesis concerns one method to harness this phase signal – propagation-based phase-contrast X-ray imaging (PBI). Three aspects on how to image complex objects are addressed: multi-material phase retrieval, simulations of clinical imaging, and small-animal imaging on compact systems. First, the derivation of a previously published method for multi-material phase retrieval is shown. A comparison between this method and another further reveals important differences. Secondly, a strategy to use large digital voxel-based phantoms for clinical imaging is developed. The method is demonstrated on a mammography phantom and in a reader study on clinical lung imaging. Finally, a compact X-ray system is used to demonstrate imaging of vascular canals in rat bone and high-resolution lung imaging on free-breathing mice, i.e., without mechanical ventilation.