New imaging modalities in high resolution X-ray tomography

For more than 100 years, X-rays are used in medical diagnostics, materials science and many other research domains for the possibility they offer to look through objects. Since the 1970s, Computed Tomography or CT allows for acquiring a full 3D representation of an object or a patient. In the 1980s, technological advances led to the development of high resolution X-ray CT or µCT. Using this technique, objects can be investigated with a spatial resolution ranging from several tens of micrometers to less than one micrometer. Despite the strong evolution in µCT, many challenges remain. Apart from several generic developments contributing to the improvement of the technique, two new imaging modalities are being investigated in this dissertation. The first modality accounts for the refraction of X-rays which contributes, along with X-ray attenuation, to the observed image. This modality is called X-ray phase contrast imaging. The second modality accounts for the energy-dependent attenuation of X-rays and allows to obtain more chemical information on the object under investigation. This modality is called spectral absorption tomography. In X-ray phase contrast imaging, the observed image contains contributions from both X-ray refraction and X-ray attenuation. Because there is no unique correlation between both effects, it is impossible to decouple both contributions from one single image, which gives rise to imaging artifacts in a classical CT reconstruction. Special reconstruction algorithms are thus required to obtain an approximated solution and to reduce imaging artifacts. In this dissertation, 4 such algorithms are elaborated and characterized based on both simulated and experimental data. In spectral absorption tomography, different images are recorded at different spectral characteristics. One method to achieve this is the usage of energy-dispersive detector systems. In this work, two such systems are discussed, using a different methodology to obtain the spectral information. The advantages and limitations of both systems are discussed and tested in the scope of acquiring three-dimensional chemical information non-destructively