Spectral Computed Tomography at High Photon Fluxes

The development of pixelated photon counting semiconductor detectors enables to resolve the spectral composition of the incident photons in X-ray imaging, provided that the detector is operated in the absence of pulse pile-up and sensor polarisation. The purpose of this study is to examine the imaging properties of Medipix2 MXR detectors under high photon fluxes, which do not meet this requirement. At first, it is shown that the critical photon flux, at which the detector’s linearity breaks down, can be shifted towards higher values by increasing the IKrum current in the charge sensitive preamplifier, which corresponds to reducing the pulse shaping time. The negative impact of this procedure on the detector’s spectroscopic performance seems only moderate. Furthermore, the deviation from an ideal linear response is determined as a function of the photon flux. The deviations are used to correct single projections and eventually acquire spectral CT images at high photon fluxes which contain corrected absorption coefficients. Thus, K-edge imaging with the contrast agents iodine and gadolinium can be performed at high photon fluxes. It is shown that the spectroscopic information vanishes for energy ranges, which correspond to energies higher than approximately the mean photon energy of the incident spectrum.

Level thesis:degree_level

master

Grantor dc:publisher

Universität Heidelberg

Year

2012

Author dc:creator

• Rink, Kristian

Contributors dc:contributor

• Oelfke, Uwe

Repository record source_url

http://www.ub.uni-heidelberg.de/archiv/21616

OAI identifier oai:identifier

oai:archiv.ub.uni-heidelberg.de:21616