@article{KhodaverdiChatziioannouWeberetal.2005,
  author    = {Khodaverdi, M. and Chatziioannou, A. F. and Weber, S. and Ziemons, Karl and Halling, H. and Pietrzyk, U.},
  title     = {Investigation of different MicroCT scanner configurations by GEANT4 simulations},
  series = {IEEE Transactions on Nuclear Science},
  volume    = {52},
  journal   = {IEEE Transactions on Nuclear Science},
  number    = {1},
  isbn      = {0018-9499},
  pages     = {188 -- 192},
  year      = {2005},
  abstract  = {This study has been performed to design the combination of the new ClearPET (ClearPET is a trademark of the Crystal Clear Collaboration), a small animal positron emission tomography (PET) system, with a micro-computed tomography (microCT) scanner. The properties of different microCT systems have been determined by simulations based on GEANT4. We will demonstrate the influence of the detector material and the X-ray spectrum on the obtained contrast. Four different detector materials (selenium, cadmium zinc telluride, cesium iodide and gadolinium oxysulfide) and two X-ray spectra (a molybdenum and a tungsten source) have been considered. The spectra have also been modified by aluminum filters of varying thickness. The contrast between different tissue types (water, air, brain, bone and fat) has been simulated by using a suitable phantom. The results indicate the possibility to improve the image contrast in microCT by an optimized combination of the X-ray source and detector material.},
  language  = {en}
}
@article{StreunChristHellendungetal.2005,
  author    = {Streun, M. and Christ, D. and Hellendung, A. and Larue, H. and Ziemons, Karl and Halling, H.},
  title     = {Effects of crosstalk and gain nonuniformity using multichannel PMTs in the Clearpet® scanner},
  series = {Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment},
  volume    = {537},
  journal   = {Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment},
  number    = {1-2},
  isbn      = {0168-9002},
  pages     = {402 -- 405},
  year      = {2005},
  abstract  = {The ClearPET® scanners developed by the Crystal Clear Collaboration use multichannel PMTs as photodetectors with scintillator pixels coupled individually to each channel. In order to localize an event each channel anode is connected to a comparator that triggers when the anode signal exceeds a common predefined threshold. Two major difficulties here are crosstalk of light and the gain nonuniformity of the PMT channels. Crosstalk can generate false triggering in channels adjacent to the actual event. On the one hand this can be suppressed by sufficiently increasing the threshold, but on the other hand a threshold too high can already prevent valid events on the lower gain channels from being detected. Finally, both effects restrict the dynamic range of pulse heights that can be processed. The requirements to the dynamic range are not low as the ClearPET® scanners detect the depth of interaction by phoswich pixels consisting of LSO and Lu0.7Y0.3AP, two scintillators with different light yields. We will present a model to estimate the achievable dynamic range and show solutions to increase it.},
  language  = {en}
}