Abstract:

X-ray fluorescence (XRF) tomography is an emerging bio-imaging modality with potential for high-resolution molecular imaging in 3D. In this technique the fluorescence signal from targeted nanoparticles (NPs) is measured, providing information about the spatial distribution and concentration of the NPs inside the object. However, present laboratory XRF tomographysystems typically have limited spatial resolution (>1 mm) and suffer from long scan times and high radiation dose even at high NP concentrations, mainly due to low efficiency and poor signal-to-noise ratio (SNR). Other macroscopic biomedical imaging methods provide either structural information with high spatial resolution (e.g., CT) or functional/molecularinformation with lower resolution (e.g., PET).

In this Thesis we present a laboratory XRF tomography system with high spatial resolution (sub-200 μm), low NP concentration and vastly reduced scan times and dose, opening up the possibilities for in vivo small-animal imaging research. The system consists of a high-brightness liquid-metal-jet microfocus x-ray source, x-ray focusing optics and two photon counting detectors. By using the source’s characteristic 24 keV line emission together with spectrally matched molybdenum NPs the Compton background is greatly reduced, increasing the SNR. Each measurement provides information about the spatial distribution and concentration of the NPs, as well as the absorption of the object. An iterative method is used to get aquantitative reconstruction of the XRF image. The reconstructed absorption and XRF images are finally combined into a single 3D overlay image.

Using this system we have demonstrated high-resolution dual CT and XRF imaging of both phantoms and mice at radiation doses compatible with in vivo small-animal imaging.