Absorption Image Correction in X-ray Talbot-Lau Interferometry for Reconstruction

Type: BA thesis

Status: finished

Date: May 18, 2020 - October 18, 2020

Supervisors: Lina Felsner, Christian Riess, Tino Haderlein, Andreas Maier

X-ray Phase-Contrast Imaging (PCI) is an imaging technique that measures the refraction of X-rays created by an object. There are several ways to realize PCI, such as interferometric and analyzer-based methods [3]. In contrast to X-ray absorption imaging, the phase image provides high soft-tissue contrast.
The implementation by a grating-based interferometer enables measuring an X-ray absorption image, a differential phase image and a dark-field image [2, p. 192-205]. Felsner et al. proposed the integration of a Tablot-Lau Interferometer (TLI) into an existing clinical CT system [1]. Three different gratings are mounted between the X-ray tube and the detector: two in front of the object, one behind (see Fig. 1). Currently it is not possible to install gratings with a diameter of more than a few centimeters because of various reasons [1]. The consequence is that it is only possible to create a phase-contrast image for a small area.
Nevertheless, for capturing the absorption image the entire size of the detector can be used. However, the absorption image is influenced by the gratings as they induce inhomogeneous exposure of the X-ray detector.
Besides that, the intensity values change with each projection. The X-ray tube, detector and gratings are rotating around the object during the scanning process. Depending on their position, parts of the object are covered by grating G 1 for one period of the rotation but not always.
It is expected that the part of the absorption image covered by the gratings differs from the rest of the image in its intensity values. Also, a sudden change in the intensity values can be detected at the edge of the lattice. This may lead to artifacts in 3-D reconstruction.
In this work, we will investigate the anticipated artifacts in the reconstruction and implement (at least) one correction algorithm. Furthermore, the reconstruction results with and without a correction algorithm will be evaluated using simulated and/or real data.

[1] L. Felsner, M. Berger, S. Kaeppler, J. Bopp, V. Ludwig, T. Weber, G. Pelzer, T. Michel, A. Maier, G. Anton, and C. Riess. Phase-sensitive region-of-interest computed tomography. In International Conference on Medical Image Computing and Computer-Assisted Intervention, pages 137–144, Cham, 2018. Springer.
[2] A. Maier, S. Steidl, V. Christlein, and J. Hornegger. Medical Imaging Systems: An Introductory Guide, volume 11111. Springer, Cham, 2018.
[3] F. Pfeiffer, T. Weitkamp, O. Bunk, and C. David. Phase retrieval and differential phase-contrast imaging with low-brilliance X-ray sources. Nature Physics, 2(4):258–261, 2006.