@article{TaylorSchmitzZiemonsetal.2000, author = {Taylor, J. G. and Schmitz, N. and Ziemons, Karl and Grosse-Ruyken, M.-L. and Gruber, O. and M{\"u}ller-G{\"a}rtner, H.-W. and Shah, N. J.}, title = {The network of brain areas involved in the motion aftereffect}, series = {Neuroimage}, volume = {11}, journal = {Neuroimage}, number = {4}, isbn = {1053-8119}, pages = {257 -- 270}, year = {2000}, abstract = {A network of brain areas is expected to be involved in supporting the motion aftereffect. The most active components of this network were determined by means of an fMRI study of nine subjects exposed to a visual stimulus of moving bars producing the effect. Across the subjects, common areas were identified during various stages of the effect, as well as networks of areas specific to a single stage. In addition to the well-known motion-sensitive area MT the prefrontal brain areas BA44 and 47 and the cingulate gyrus, as well as posterior sites such as BA37 and BA40, were important components during the period of the motion aftereffect experience. They appear to be involved in control circuitry for selecting which of a number of processing styles is appropriate. The experimental fMRI results of the activation levels and their time courses for the various areas are explored. Correlation analysis shows that there are effectively two separate and weakly coupled networks involved in the total process. Implications of the results for awareness of the effect itself are briefly considered in the final discussion.}, language = {en} } @article{FinkMarshallShahetal.2000, author = {Fink, G. R. and Marshall, J. C. and Shah, N. J. and Weiss, P.H. and Halligan, P. W. and Grosse-Ruyken, M. and Ziemons, Karl and Zilles, K. and Freund, H. J.}, title = {Line bisection judgments implicate right parietal cortex and cerebellum as assessed by fMRI}, series = {Neurology}, volume = {54}, journal = {Neurology}, number = {6}, isbn = {1526-632X}, pages = {1324 -- 1331}, year = {2000}, language = {en} } @article{StreunBrandenburgLarueetal.2000, author = {Streun, M. and Brandenburg, G. and Larue, H. and Zimmermann, E. and Ziemons, Karl and Halling, H.}, title = {Pulse recording by free-running sampling}, series = {2000 IEEE Nuclear Science Symposium Conference Record, Vol. 2}, journal = {2000 IEEE Nuclear Science Symposium Conference Record, Vol. 2}, issn = {1082-3654}, pages = {9/179 -- 9/181}, year = {2000}, abstract = {Pulses from a position-sensitive photomultiplier (PS-PMT) are recorded by free running ADCs at a sampling rate of 40 MHz. A four-channel acquisition-board has been developed which is equipped with four 12 bit-ADCs connected to one FPGA (field programmable gate array). The FPGA manages data acquisition and the transfer to the host computer. It can also work as a digital trigger, so a separate hardware-trigger can be omitted. The method of free running sampling provides a maximum of information, besides the pulse charge and amplitude also pulse shape and starting time are contained in the sampled data. These informations are crucial for many tasks such as distinguishing between different scintillator materials, determination of radiation type, pile-up recovery, coincidence detection or time-of-flight applications. The absence of an analog integrator allows coping with very high count rates. Since this method is going to be employed in positron emission tomography (PET), the position of an event is another important information. The simultaneous readout of four channels allows localization by means of center-of-gravity weighting. First results from a test setup with LSO-scintillators coupled to the PS-PMT are presented}, language = {en} } @article{StreunBrandenburgLarueetal.2001, author = {Streun, M. and Brandenburg, G. and Larue, H. and Zimmermann, E. and Ziemons, Karl and Halling, H.}, title = {Pulse recording by free-running sampling}, series = {IEEE Transactions on Nuclear Science}, volume = {48}, journal = {IEEE Transactions on Nuclear Science}, number = {3}, isbn = {0018-9499}, pages = {524 -- 526}, year = {2001}, abstract = {Pulses from a position-sensitive photomultiplier (PS-PMT) are recorded by free-running ADCs at a sampling rate of 40 MHz. A four-channel acquisition board has been developed which is equipped with four 12-bit ADCs connected to one field programmable gate array (FPGA). The FPGA manages data acquisition and the transfer to the host computer. It can also work as a digital trigger, so a separate hardware trigger can be omitted. The method of free-running sampling provides a maximum of information, besides the pulse charge and amplitude also pulse shape and starting time are contained in the sampled data. This information is crucial for many tasks such as distinguishing between different scintillator materials, determination of radiation type, pile-up recovery, coincidence detection or time-of-flight applications. The absence of an analog integrator allows very high count rates to be dealt with. Since this method is to be employed in positron emission tomography (PET), the position of an event is also important. The simultaneous readout of four channels allows localization by means of center-of-gravity weighting. First results from a test setup with LSO scintillators coupled to the PS-PMT are presented here}, language = {en} } @article{HeinrichBlumBussmannetal.2002, author = {Heinrich, U. and Blum, A. and Bussmann, N. and Engels, R. and Kemmerling, G. and Weber, S. and Ziemons, Karl}, title = {Statistical studies on the light output and energy resolution of small LSO single crystals with different surface treatments combined with various reflector materials}, series = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, volume = {486}, journal = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, number = {1-2}, issn = {0168-9002}, pages = {60 -- 66}, year = {2002}, abstract = {The optimization of light output and energy resolution of scintillators is of special interest for the development of high resolution and high sensitivity PET. The aim of this work is to obtain statistically reliable results concerning optimal surface treatment of scintillation crystals and the selection of reflector material. For this purpose, raw, mechanically polished and etched LSO crystals (size 2×2×10 mm3) were combined with various reflector materials (Teflon tape, Teflon matrix, BaSO4) and exposed to a 22Na source. In order to ensure the statistical reliability of the results, groups of 10 LSO crystals each were measured for all combinations of surface treatment and reflector material. Using no reflector material the light output increased up to 551±35\% by mechanical polishing the surface compared to 100±5\% for raw crystals. Etching the surface increased the light output to 441±29\%. The untreated crystals had an energy resolution of 24.6±4.0\%. By mechanical polishing the surface it was possible to achieve an energy resolution of 13.2±0.8\%, by etching of 14.8±0.7\%. In combination with BaSO4 as reflector material the maximum increase of light output has been established to 932±57\% for mechanically polished and 895±61\% for etched crystals. The combination with BaSO4 also caused the best improvement of the energy resolution up to 11.6±0.2\% for mechanically polished and 12.2±0.3\% for etched crystals. Relating to the light output there was no significant statistical difference between the two surface treatments in combination with BaSO4. In contrast to this, the statistical results of the energy resolution have shown the combination of mechanical polishing and BaSO4 as the optimum.}, language = {en} } @article{StreunBrandenburgLarueetal.2002, author = {Streun, M. and Brandenburg, G. and Larue, H. and Zimmermann, E. and Ziemons, Karl and Halling, H.}, title = {A PET system with free running ADCs}, series = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, volume = {486}, journal = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, number = {1-2}, issn = {0168-9002}, pages = {18 -- 21}, year = {2002}, abstract = {A small PET system has been built up with two multichannel photomultipliers, which are attached to a matrix of 64 single LSO crystals each. The signal from each multiplier is being sampled continuously by a 12 bit ADC at a sampling frequency of 40 MHz. In case of a scintillation pulse a subsequent FPGA sends the corresponding set of samples together with the channel information and a time mark to the host computer. The data transfer is performed with a rate of 20 MB/s. On the host all necessary information is extracted from the data. The pulse energy is determined, coincident events are detected and multiple hits within one matrix can be identified. In order to achieve a narrow time window the pulse starting time is refined further than the resolution of the time mark (=25 ns) would allow. This is possible by interpolating between the pulse samples. First data obtained from this system will be presented. The system is part of developments for a much larger system and has been created to study the feasibility and performance of the technique and the hardware architecture.}, language = {en} } @article{StreunBrandenburgLarueetal.2002, author = {Streun, M. and Brandenburg, G. and Larue, H. and Zimmermann, E. and Ziemons, Karl and Halling, H.}, title = {Coincidence detection by digital processing of free-running sampled pulses}, series = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, volume = {487}, journal = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, number = {3}, isbn = {0168-9002}, pages = {530 -- 534}, year = {2002}, abstract = {Coincident events in two scintillator crystals coupled to photomultipliers (PMT) are detected by processing just the digital data of the recorded pulses. For this purpose the signals from both PMTs are continuously sampled by free-running ADCs at a sampling rate of 40 MHz. For each sampled pulse the starting time is determined by processing the pulse data. Even a fairly simple interpolating algorithm results in a FWHM of about 2 ns.}, language = {en} } @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{StreunBrandenburgLarueetal.2006, author = {Streun, M. and Brandenburg, G. and Larue, H. and Parl, C. and Ziemons, Karl}, title = {The data acquisition system of ClearPET neuro - a small animal PET scanner}, series = {IEEE Transactions on Nuclear Science}, volume = {53}, journal = {IEEE Transactions on Nuclear Science}, number = {3}, isbn = {0018-9499}, pages = {700 -- 703}, year = {2006}, abstract = {The Crystal Clear Collaboration has developed a modular system for a small animal PET scanner (ClearPET). The modularity allows the assembly of scanners of different sizes and characteristics in order to satisfy the specific needs of the individual member institutions. The system performs depth of interaction detection by using a phoswich arrangement combining LSO and LuYAP scintillators which are coupled to Multichannel Photomultipliers (PMTs). For each PMT a free running 40 MHz ADC digitizes the signal and the complete scintillation pulse is sampled by an FPGA and sent with 20 MB/s to a PC for preprocessing. The pulse provides information about the gamma energy and the scintillator material which identifies the interaction layer. Furthermore, the exact pulse starting time is obtained from the sampled data. This is important as no hardware coincidence detection is implemented. All single events are recorded and coincidences are identified by software. The system in J{\"u}lich (ClearPET Neuro) is equipped with 10240 crystals on 80 PMTs. The paper will present an overview of the data acquisition system.}, language = {en} } @article{KhodaverdiWeberStreunetal.2006, author = {Khodaverdi, M. and Weber, S. and Streun, M. and Parl, C. and Ziemons, Karl}, title = {High resolution imaging with ClearPET™ Neuro - first animal images}, series = {2005 IEEE Nuclear Science Symposium Conference Record, Vol. 3}, journal = {2005 IEEE Nuclear Science Symposium Conference Record, Vol. 3}, isbn = {1082-3654}, pages = {1641 -- 1644}, year = {2006}, abstract = {The ClearPET™ Neuro is the first full ring scanner within the Crystal Clear Collaboration (CCC). It consists of 80 detector modules allocated to 20 cassettes. LSO and LuYAP:Ce crystals in phoswich configuration in combination with position sensitive photomultiplier tubes are used to achieve high sensitivity and realize the acquisition of the depth of interaction (DOI) information. The complete system has been tested concerning the mechanical and electronical stability and interplay. Moreover, suitable corrections have been implemented into the reconstruction procedure to ensure high image quality. We present first results which show the successful operation of the ClearPET™ Neuro for artefact free and high resolution small animal imaging. Based on these results during the past few months the ClearPET™ Neuro System has been modified in order to optimize the performance.}, language = {en} }