@article{ZiemonsBruyndonckxPerezetal.2008,
  author    = {Ziemons, Karl and Bruyndonckx, P. and Perez, J. M. and Pietrzyk, U. and Rato, P. and Tavernier, S.},
  title     = {Beyond ClearPET: Next Aims},
  series = {5th IEEE International Symposium on Biomedical Imaging: From Nano to Macro Symposium Proceedings ISBI 2008},
  journal   = {5th IEEE International Symposium on Biomedical Imaging: From Nano to Macro Symposium Proceedings ISBI 2008},
  isbn      = {978-1-4244-2003-2},
  pages     = {1421 -- 1424},
  year      = {2008},
  abstract  = {The CRYSTAL CLEAR collaboration, in short CCC, is a consortium of 12 academic institutions, mainly from Europe, joining efforts in the area of developing instrumentation for nuclear medicine and medical imaging. In the framework of the CCC a high performance small animal PET system, called ClearPET, was developed by using new technologies in electronics and crystals in a phoswich arrangement combining two types of lutetium- based scintillator materials: LSO:Ce and LuYAP:Ce. Our next aim will be the development of hybrid image systems. Hybrid MR-PET imaging has many unique advantages for brain research. This has sparked a new research line within CCC for the development of novel MR-PET compatible technologies. MRI is not as sensitive as PET but PET has poorer spatial resolution than MRI. Two major advantages of PET are sensitivity and its ability to acquire metabolic information. To assess these innovations, the development of a 9.4T hybrid animal MR-PET scanner is proposed based on an existing 9.4T MR scanner that will be adapted to enable simultaneous acquisition of MR and PET data using cutting- edge technology for both MR and PET.},
  language  = {en}
}
@article{HeinrichsPietrzykZiemons2003,
  author    = {Heinrichs, U. and Pietrzyk, U. and Ziemons, Karl},
  title     = {Design optimization of the PMT-ClearPET prototypes based on simulation studies with GEANT3},
  series = {2002 IEEE Nuclear Science Symposium Conference Record, Vol. 3},
  journal   = {2002 IEEE Nuclear Science Symposium Conference Record, Vol. 3},
  issn      = {1082-3654},
  pages     = {682 -- 686},
  year      = {2003},
  abstract  = {Within the Crystal Clear Collaboration four centres are developing 2nd generation high performance small animal PET scanners for different kinds of animals and medical applications. The first prototypes are PMT-based systems including depth of interaction (DOI) detection by using a phoswich layer of LSO and LuYAP. The aim of these simulation studies is to optimize sensitivity and spatial resolution of given designs, which vary in FOVs caused by different detector configurations (ring/octagon) and sizes. For this purpose the simulation tool GEANT3 (CERN) was used. The simulations have shown that all PMT designs with one-to-one coupling of crystals have a very nonlinear axial sensitivity profile. By shifting every other PMT 1/4 of a PMT length in axial direction the sampling of the FOVs became more homogeneous. At an energy threshold of 350keV the regression coefficient increases from 0.818 for the non-shifted to 0.993 for the shifted design. Simulations of a point source centred in the FOV (threshold: 350keV) resulted in sensitivities of 4.2\% for a 4×20PMT (LSO/LuYAP a 10mm) and 3.8\% for a 4×16PMT (LSO/LuYAP a 8mm) ring design. The 3D-MLEM reconstruction of a point source shows the enormous improvement of resolution using a crystal double layer with DOI (3.1mm at 40mm from CFOV) instead of a 20mm single layer (11.9mm).},
  language  = {en}
}
@article{HeinrichsPietrzykZiemons2003,
  author    = {Heinrichs, U. and Pietrzyk, U. and Ziemons, Karl},
  title     = {Design optimization of the PMT-ClearPET prototypes based on simulation studies with GEANT3},
  series = {IEEE Transactions on Nuclear Science},
  volume    = {50},
  journal   = {IEEE Transactions on Nuclear Science},
  number    = {5},
  isbn      = {0018-9499},
  pages     = {1428 -- 1432},
  year      = {2003},
  abstract  = {Within the Crystal Clear Collaboration (CCC), four centers are developing second generation high performance small animal positron emission tomography (PET) scanners for different kinds of animals and medical applications. The first prototypes are photomultiplier tube (PMT)-based systems including depth of interaction (DOI) detection by using a phoswich layer of lutetium oxyorthosilicate (LSO) and lutetium yttrium aluminum perovskite (LuYAP). The aim of these simulation studies is to optimize sensitivity and spatial resolution of given designs, which vary in fields of view (FOVs) caused by different detector configurations (ring/octagon) and sizes. For this purpose the simulation tool GEANT3 (CERN, Geneva, Switzerland) was used.},
  language  = {en}
}
@article{SchollSchubertZieneretal.2010,
  author    = {Scholl, Ingrid and Schubert, N. and Ziener, P. and Pietrzyk, U.},
  title     = {GPU-basiertes Volumenrendering von multimodalen medizinischen Bilddaten in Echtzeit},
  series = {Bildverarbeitung f{\"u}r die Medizin 2010 : Algorithmen, Systeme, Anwendungen ; Proceedings des Workshops vom 14. bis 16. M{\"a}rz in Aachen / Thomas M. Deserno ... (Hrsg.)},
  journal   = {Bildverarbeitung f{\"u}r die Medizin 2010 : Algorithmen, Systeme, Anwendungen ; Proceedings des Workshops vom 14. bis 16. M{\"a}rz in Aachen / Thomas M. Deserno ... (Hrsg.)},
  publisher = {Springer},
  address   = {Berlin},
  isbn      = {978-3-642-11967-5},
  pages     = {400 -- 404},
  year      = {2010},
  language  = {de}
}
@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{KhodaverdiChaziioannouWeberetal.2004,
  author    = {Khodaverdi, M. and Chaziioannou, 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 = {2003 IEEE Nuclear Science Symposium Conference Record, Vol. 4},
  journal   = {2003 IEEE Nuclear Science Symposium Conference Record, Vol. 4},
  issn      = {1082-3654},
  pages     = {2989 -- 2993},
  year      = {2004},
  abstract  = {This study has been performed to design the combination of the new ClearPET TM (ClearPET is a trademark of the Crystal Clear Collaboration), a small animal Positron Emission Tomography (PET) system, with a microComputed Tomography (microCT) scanner. The properties of different microCT systems have been determined by simulations based on GEANT4. We 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}
}
@inproceedings{StreunAlKaddoumParletal.2012,
  author    = {Streun, M. and Al-Kaddoum, R. and Parl, C. and Pietrzyk, U. and Ziemons, Karl and Waasen, S. van},
  title     = {Simulation studies of optical photons in monolithic block scintillators},
  series = {2011 IEEE Nuclear Science Symposium Conference Record (NSS/MIC)},
  booktitle = {2011 IEEE Nuclear Science Symposium Conference Record (NSS/MIC)},
  publisher = {IEEE},
  address   = {New York},
  isbn      = {978-1-4673-0120-6 (electronic ISBN)},
  doi       = {10.1109/NSSMIC.2011.6154621},
  pages     = {1380 -- 1382},
  year      = {2012},
  abstract  = {The interest in PET detectors with monolithic block scintillators is growing. In order to obtain high spatial resolutions dedicated positioning algorithms are required. But even an ideal algorithm can only deliver information which is provided by the detector. In this simulation study we investigated the light distribution on one surface of cuboid LSO scintillators of different size. Scintillators with a large aspect ratio (small footprint and large height) showed significant position information only for a minimum interaction depth of the gamma particle. The results allow a quantitative estimate for a useful aspect ratio.},
  language  = {en}
}
@article{ZiemonsHeinrichsStreunetal.2004,
  author    = {Ziemons, Karl and Heinrichs, U. and Streun, M. and Pietrzyk, U.},
  title     = {Validation of GEANT3 simulation studies with a dual-head PMT ClearPET™ prototype},
  series = {2003 IEEE Nuclear Science Symposium Conference Record, Vol. 5},
  journal   = {2003 IEEE Nuclear Science Symposium Conference Record, Vol. 5},
  issn      = {1082-3654},
  pages     = {3053 -- 3056},
  year      = {2004},
  abstract  = {The ClearPET™ project is proposed by working groups of the Crystal Clear Collaboration (CCC) to develop a 2nd generation high performance small animal positron emission tomograph (PET). High sensitivity and high spatial resolution is foreseen for the ClearPET™ camera by using a phoswich arrangement combining mixed lutetium yttrium aluminum perovskite (LuYAP:Ce) and lutetium oxyorthosilicate (LSO) scintillating crystals. Design optimizations for the first photomultiplier tube (PMT) based ClearPET camera are done with a Monte-Carlo simulation package implemented on GEANT3 (CERN, Geneva, Switzerland). A dual-head prototype has been built to test the frontend electronics and was used to validate the implementation of the GEANT3 simulation tool. Multiple simulations were performed following the experimental protocols to measure the intrinsic resolution and the sensitivity profile in axial and radial direction. Including a mean energy resolution of about 27.0\% the simulated intrinsic resolution is about (1.41±0.11)mm compared to the measured of (1.48±0.06)mm. The simulated sensitivity profiles show a mean square deviation of 12.6\% in axial direction and 3.6\% in radial direction. Satisfactorily these results are representative for all designs and confirm the scanner geometry.},
  language  = {en}
}