Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. This paper gives a detailed description of the design and development of GATE by the OpenGATE collaboration, whose continuing objective is to improve, document and validate GATE by simulating commercially available imaging systems for PET and SPECT. Large effort is also invested in the ability and the flexibility to model novel detection systems or systems still under design. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at http:/www-lphe.epfl.ch/GATE/. Two benchmarks developed for PET and SPECT to test the installation of GATE and to serve as a tutorial for the users are presented. Extensive validation of the GATE simulation platform has been started, comparing simulations and measurements on commercially available acquisition systems. References to those results are listed. The future prospects towards the gridification of GATE and its extension to other domains such as dosimetry are also discussed.

/pdf/gate-a-simulation-toolkit-for-pet-and-spect-i05cuwekfu.pdf

GATE : a simulation toolkit for PET and SPECT

Energy of the first 4f7→4f65d transition of Eu2+ in inorganic compounds

The 5d level positions of the trivalent lanthanides in inorganic compounds

The absorption and emission cross sections of the transition between the ground spin-orbit multiplet and the lowest excited multiplet were measured for Er/sup 3+/, Tm/sup 3+/, and Ho/sup 3+/ ions in a variety of crystalline hosts. The materials that were investigated include LiYF/sub 4/, BaY/sub 2/F/sub 8/, Y/sub 3/Al/sub 5/O/sub 12/, LaF/sub 3/, KCaF/sub 3/, YAlO/sub 3/, and La/sub 2/Be/sub 2/O/sub 5/. The absolute magnitudes of the emission cross sections were determined from the absorption spectra, with the aid of the principle of reciprocity. The calculated radiative emission lifetimes derived from these measured cross sections agree well with the measured emission decay times for most materials. The potential use of these rare-earth-doped materials in pulsed laser applications requires that the ground state exhibit adequate splitting to minimize the detrimental effects of the ground state thermal population, and also that the emission cross section be sufficiently large to permit efficient extraction energy. The systems based on Ho/sup 3+/ in the eightfold coordinated sites of LiYF/sub 4/, BaY/sub 2/F/sub 8/, and Y/sub 3/Al/sub 5/O/sub 12/ appear to be the most promising. >

Infrared cross-section measurements for crystals doped with Er/sup 3+/, Tm/sup 3+/, and Ho/sup 3+/

Design of luminescent lanthanide complexes: From molecules to highly efficient photo-emitting materials

Photoionization and luminescences in BaF2:Eu2+

In this paper, we analyze the fluorescence and the photoconductivity properties of Yb 2+ in CaF 2 , SrF 2 and BaF 2 . We present a new approach to the interpretation of the «anomalous» emission usually observed in such systems by an impurity trapped exciton which is the lowest excited state of the system. We show that the excited «d» electron of Yb 2+ is delocalized in the «s» orbitals of next neighbor Ca 2+ ions from where it can either autoionize or recombine with Yb 3+ giving rise to the red shifted luminescence. The photoconductivity spectra show that when the electron is excited into the higher energy bands it autoionizes without any prior relaxation. The strong temperature dependence of lifetime shows that the exciton level is split into two close levels and the study of the risetime of the decays allow us to calculate the energy of E u , T 2u level and the probability of tunneling from this level into the exciton level Dans cet article, on analyse les proprietes de fluorescence et de photoconductivite de Yb 2+ dans CaF 2 , SrF 2 et BaF 2 . On presente une nouvelle interpretation de l'emission «anormale» habituelement observee dans de tels systemes par un exciton piege sur l'impurete. On montre que l'electron «d» de Yb 2+ excite se delocalise dans les orbitales «s» des ions Ca 2+ voisins a partir d'ou il peut soit s'auto-ioniser soit se recombiner avec l'ion Yb 3+ en donnant la luminescence decalee vers le rouge. Les spectres de photoconductivite montrent que lorsque l'electron est excite dans les bandes de haute energie il s'auto-ionise sans relaxation prealable. La forte variation thermique des durees de vie montre que le niveau excitonique est scinde en deux sous-niveaux tres proches et l'etude du temps de montee permet de calculer l'energie du niveau E u , T 2u ainsi que la probabilite de l'effet tunnel entre ce niveau et l'exciton

C. Pedrini

Papers

Photoionization and luminescences in BaF2:Eu2+

Luminescence and photoionization processes of Yb2+ in CaF 2, SrF2 and BaF2

Bridgman growth and site occupation in LuAG:Ce scintillator crystals

Efficient and stable pulsed laser operation of Ce:LiLuF4 around 308 nm

Optical and scintillation properties of Ce3+ doped LiYF4 and LiLuF4 crystals