PhD defense by Erik Schou Dreier

Novel direct conversion X-ray detectors with single-photon sensitivity have the potential to improve several X-ray imaging techniques. These detectors' ability to perform "color" (energy resolved) X-ray imaging has already now shown to improving the material discrimination abilities of airport X-ray luggage scanners. However, spectrum distorting effects, such as the so-called charge sharing, may deteriorate the quality of the material discrimination and affect the detectors' image resolution.

In my thesis, I show how the quality of the X-ray spectra can be improved using a comprehensive, computational correction algorithm that I developed during my PhD. The algorithm is based on numerical simulations and analytical models of the direct converting X-ray detectors.

In my thesis I further demonstrate how the fast and novel Timepix3 readout chip with 55 µm pixel size can obtain single-photon localization precision of less than 19 µm using charge sharing. I exploit this single-photon localization to present the first multi-contrast imaging setup with directional scattering sensitivity using the so-called beam-tracking technique. Multi-contrast imaging allows for a simultaneous measurement of conventional X-ray attenuation (known from clinical X-rays), X-ray refraction, and X-ray scattering. The refraction contrast is used to increase the sensitivity for low absorbing materials, and the scattering contrast enables the measurement of objects small than the image resolution. This method can potentially make 3 dimensional microstructure imaging both cheaper and faster, and, thereby, more accessible in a range of applications within fundamental research.

Principal Supervisor Brian Vinter


Ulrik Lund Olsen and Robert Feidenhans’l

Assessment Committee

Associate Professor Heloisa Nunes Bordallo, NBI
Professor Julia Herzen, Technical University of Munich
Head of the Detector Group, European XFEL Markus Kuster, XFEL GmbH, Schenefeld

Leader of defence: Heloisa Nunes Bordallo, NBI