Pilot Studies for Quantitative 2D and 3D X-Ray Fluorescence Imaging

Abstract

X-ray-fluorescence imaging (XFI) is an emerging functional imaging modality promising benefits for tumor detection, cell-tracking and pharmacokinetics. When matter is irradiated by an external x-ray beam, fluorescence photons in the x-ray regime characteristic for the elemental composition are emitted. By using non-endogenous high- or medium-Z elements as markers, this principle can be employed in a functional imaging modality. One challenge in this method is separating the fluorescence photons from background events, mostly created by Compton scattering. For achieving the highest sensitivities in XFI, a mono-energetic incident beam is thus needed, making synchrotrons the ideal x-ray source for XFI. However, the special characteristics of a synchrotron beamline have to be taken into account for the design of the experimental setup. In the scope of this thesis, a series of pilot studies were performed to understand and optimize all aspects required to apply the principle of XFI to synchrotron-based in-vivo immune cell tracking at the P21.1 beamline at the Petra III synchrotron. Furthermore, a new reconstruction method is investigated which allows to reduce the radiation dose of three-dimensional spatial imaging of the fluorescence marker distribution. Combining the results, three-dimensional reconstruction of organ concentrations down to 650 ng/ml at in-vivo conform radiation levels are achievable, promising to allow tracking multiple types of cells simultaneously.