Search

Abstract: In this paper we discuss the physical processes from the first interaction of an X-ray photon to the spatial distribution of charge carriers at the electrodes of a pixel detector. The implications of these processes on the achievable position and energy resolution have been investigated with simulation calculations and with measurements employing the Medipix detectors. As the next generation detectors will be capable of energy resolution we present two methods of energy exploitation in X-ray imaging, i.e. energy weighting and material reconstruction. [Copyright &y& Elsevier]

Abstract: In the last decades, phase-contrast imaging using a Talbot–Lau grating interferometer is possible even with a low-brilliance X-ray source. With the potential of increasing the soft-tissue contrast, this method is on its way into medical imaging. For this purpose, the knowledge of the underlying physics of this technique is necessary. With this paper, we would like to contribute to the understanding of grating-based phase-contrast imaging by presenting results on measurements and simulations regarding the noise behaviour of the differential phases. These measurements were done using a microfocus X-ray tube with a hybrid, photon-counting, semiconductor Medipix2 detector. The additional simulations were performed by our in-house developed phase-contrast simulation tool “SPHINX”, combining both wave and particle contributions of the simulated photons. The results obtained by both of these methods show the same behaviour. Increasing the number of photons leads to a linear decrease of the standard deviation of the phase. The number of used phase steps has no influence on the standard deviation, if the total number of photons is held constant. Furthermore, the probability density function (pdf) of the reconstructed differential phases was analysed. It turned out that the so-called von Mises distribution is the physically correct pdf, which was also confirmed by measurements. This information advances the understanding of grating-based phase-contrast imaging and can be used to improve image quality. [Copyright &y& Elsevier]

Abstract: In this paper we present results from simulations on grating-based phase contrast imaging. Herein, the performance of a grating-based interferometer concerning the X-ray''s energy is shown. Additionally, geometric parameters of the interferometer were investigated. In the experimental part of this work we present the dependency of the Talbot-Lau interferometer setup on the lower energy threshold of the Medipix-detector. These are the first energy sensitive measurements acquired within the applied method. Furthermore, we demonstrate the difference between a differential and an integral measurement by comparing the phase and absorption image. The conclusion of this work is the detailed characterisation of grating-based phase contrast imaging regarding its energy dependent behaviour and geometric parameters of the gratings. [Copyright &y& Elsevier]

Abstract: We outline in this paper that the noise of a photon counting pixel detector depends on the detection efficiency and the average multiplicity of counts per interacting photon. We give a simple expression for the signal-to-noise ratio (SNR) and zero-frequency detective quantum efficiency (DQE). We describe a method to determine the DQE from measured data and to optimize the DQE as a function of energy threshold. [Copyright &y& Elsevier]