Validation of the GATE Monte Carlo simulation platform for modelling a CsI(Tl) scintillation camera dedicated to small animal imaging

Monte Carlo simulations are increasingly used in scintigraphic imaging to model imaging systems and to develop and assess tomographic reconstruction algorithms and correction methods for improved image quantitation. GATE (GEANT 4 Application for Tomographic Emission) is a new Monte Carlo simulation platform based on GEANT4 dedicated to nuclear imaging applications. This paper describes the GATE simulation of a prototype of scintillation camera dedicated to small animal imaging and consisting of a CsI(Tl) crystal array coupled to a position sensitive photomultiplier tube. The relevance of GATE to model the camera prototype was assessed by comparing simulated 99mTc point spread functions, energy spectra, sensitivities, scatter fractions and image of a capillary phantom with the corresponding experimental measurements. Results showed an excellent agreement between simulated and experimental data: experimental spatial resolutions were predicted with an error less than 100 mu m. The difference between experimental and simulated system sensitivities for different source-to-collimator distances was within 2%. Simulated and experimental scatter fractions in a [98-182 keV] energy window differed by less than 2% for sources located in water. Simulated and experimental energy spectra agreed very well between 40 and 180 keV. These results demonstrate the ability and flexibility of GATE for simulating original detector designs. The main weakness of GATE concerns the long computation time it requires: this issue is currently under investigation by the GEANT4 and the GATE collaboration

Characterization of high-temperature PbTe p-n junctions prepared by thermal diffusion and by ion-implantation

We describe here the characteristics of two types of high-quality PbTe p-n-junctions, prepared in this work: (1) by thermal diffusion of In4Te3 gas (TDJ), and (2) by ion implantation (implanted junction, IJ) of In (In-IJ) and Zn (Zn-IJ). The results, as presented here, demonstrate the high quality of these PbTe diodes. Capacitance-voltage and current-voltage characteristics have been measured. The measurements were carried out over a temperature range from ~ 10 K to ~ 180 K. The latter was the highest temperature, where the diode still demonstrated rectifying properties. This maximum operating temperature is higher than any of the earlier reported results. The saturation current density, J0, in both diode types, was ~ 10^-5 A/cm2 at 80 K, while at 180 K J0 ~ 10^-1 A/cm2 in TDJ and ~ 1 A/cm2 in both ion-implanted junctions. At 80 K the reverse current started to increase markedly at a bias of ~ 400 mV for TDJ, and at ~550 mV for IJ. The ideality factor n was about 1.5-2 for both diode types at 80 K. The analysis of the C-V plots shows that the junctions in both diode types are linearly graded. The analysis of the C-V plots allows also determining the height of the junction barrier, the concentrations and the concentration gradient of the impurities, and the temperature dependence of the static dielectric constant. The zero-bias-resistance x area products (R0Ae) at 80 K are: 850 OHMcm2 for TDJ, 250 OHMcm2 for In-IJ, and ~ 80 OHMcm2 for Zn-IJ, while at 180 K R0Ae ~ 0.38 OHMcm2 for TDJ, and ~ 0.1 OHMcm2 for IJ. The estimated detectivity is: D* ~ 10^10 cmHz^(1/2)/W up to T=140 K, determined mainly by background radiation, while at T=180 K, D* decreases to 108-107 cmHz^(1/2)/W, and is determined by the Johnson noise

Influence of Annealing on the Optical and Scintillation Properties of CaWO4_4 Single Crystals

We investigate the influence of oxygen annealing on the room temperature optical and scintillation properties of CaWO$_4$ single crystals that are being produced for direct Dark Matter search experiments. The applied annealing procedure reduces the absorption coefficient at the peak position of the scintillation spectrum ($\sim430$ nm) by a factor of $\sim6$ and leads to an even larger reduction of the scattering coefficient. Furthermore, the annealing has no significant influence on the \emph{intrinsic} light yield. An additional absorption occurring at $\sim400$ nm suggests the formation of O$^-$ hole centers. Light-yield measurements at room temperature where one crystal surface was mechanically roughened showed an increase of the \emph{measured} light yield by $\sim40$ and an improvement of the energy resolution at 59.5 keV by $\sim12$ for the annealed crystal. We ascribe this result to the reduction of the absorption coefficient while the surface roughening is needed to compensate for the also observed reduction of the scattering coefficient after annealing

GATE : a simulation toolkit for PET and SPECT

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. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at the address http://www-lphe.epfl.ch/GATE/

The Pre-Biblical Metallurgical Art on the Biblical Territory

The Old Testament describes in detail the metallurgical achievements, both in the period before the conquest and colonization of the promised land (mostly related to the manufacturing of the Tabernacle, in this sense, the gold chandelier with seven branches, also known as the menorah, is an exceptional example), and the period after the conquest and colonization of the promised land (the sea of bronze pillars Boaz and Jachin, the 10 golden candlesticks with seven arms, etc., famous artifacts of Solomon's Temple facilities, are good examples). Question: at that time, did the Jews have the technical and technological knowledge necessary to create things in order to reach the great achievements of the metallurgical processes described in the Old Testament? This article tries to answer this question

Spectrophotometric Determination of Os(VIII) with Nitroso R Salt as Chromogenic Reagent

Several methods have been reported for the spectrophotometric determination of osmium with various chromogenic reagents. Some of these reagents react slowly with osmium and the conditions for obtaining reproductibile colours are usually empirical. In this context, a simple and sensitive spectrophotometric method for the determination of trace amounts of osmium(VIII) using disodium-1-nitroso-2-hydroxynaphthalene-3,6-disulphonate (Nitroso R salt) is described. The method is based on the formation of an Os–Nitroso R salt complex which exhibits two different colours as function of pH. Linear calibration graphs are obtained up to 60 μg/mL of the analyte at pH = 4.8. The stoichiometry of the complex is found to be 1: 4 by mole ratio method. The method is optimized and different analytical parameters were evaluated. For instance, the calculated values for the molar absorptivity are of 3.645.103 L/mol.cm (pH = 0; λ = 550 nm) and 1.695.103 L/mol.cm (pH = 4.8; λ = 510 nm), respectively. The proposed method should be valuable for the determination of osmium(VIII) with good accuracy and precision

Feasibility Study of a Small Animal PET Insert Based on a Single LYSO Monolithic Tube

[EN] There are drawbacks with using a Positron Emission Tomography (PET) scanner design employing the traditional arrangement of multiple detectors in an array format. Typically PET systems are constructed with many regular gaps between the detector modules in a ring or box configuration, with additional axial gaps between the rings. Although this has been significantly reduced with the use of the compact high granularity SiPM photodetector technology, such a scanner design leads to a decrease in the number of annihilation photons that are detected causing lower scanner sensitivity. Moreover, the ability to precisely determine the line of response (LOR) along which the positron annihilated is diminished closer to the detector edges because the spatial resolution there is degraded due to edge effects. This happens for both monolithic based designs, caused by the truncation of the scintillation light distribution, but also for detector blocks that use crystal arrays with a number of elements that are larger than the number of photosensors and, therefore, make use of the light sharing principle. In this report we present a design for a small-animal PET scanner based on a single monolithic annulus-like scintillator that can be used as a PET insert in high-field Magnetic Resonance systems. We provide real data showing the performance improvement when edge-less modules are used. We also describe the specific proposed design for a rodent scanner that employs facetted outside faces in a single LYSO tube. In a further step, in order to support and prove the proposed edgeless geometry, simulations of that scanner have been performed and lately reconstructed showing the advantages of the design.This project was funded in part by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No 695536). It has also been supported by the Spanish Ministerio de Economia, Industria y Competitividad under Grant TEC2016-79884-C2-1-R and through PROSPET (DTS15/00152) funded by the Ministerio de Economia y Competitividad. AR is a postdoctoral fellow of the FWO (project 12T7118N). The University of Virginia School of Medicine has provided seed funding for this project.González Martínez, AJ.; Berr, SS.; Cañizares-Ledo, G.; Gonzalez-Montoro, A.; Orero Palomares, A.; Correcher Salvador, C.; Rezaei, A.... (2018). Feasibility Study of a Small Animal PET Insert Based on a Single LYSO Monolithic Tube. Frontiers in Medicine. 5:1-8. https://doi.org/10.3389/fmed.2018.00328S185Kuntner, C., & Stout, D. (2014). Quantitative preclinical PET imaging: opportunities and challenges. Frontiers in Physics, 2. doi:10.3389/fphy.2014.00012Judenhofer, M. S., & Cherry, S. R. (2013). Applications for Preclinical PET/MRI. Seminars in Nuclear Medicine, 43(1), 19-29. doi:10.1053/j.semnuclmed.2012.08.004España, S., Marcinkowski, R., Keereman, V., Vandenberghe, S., & Van Holen, R. (2014). DigiPET: sub-millimeter spatial resolution small-animal PET imaging using thin monolithic scintillators. Physics in Medicine and Biology, 59(13), 3405-3420. doi:10.1088/0031-9155/59/13/3405Yang, Y., Bec, J., Zhou, J., Zhang, M., Judenhofer, M. S., Bai, X., … Cherry, S. R. (2016). A Prototype High-Resolution Small-Animal PET Scanner Dedicated to Mouse Brain Imaging. Journal of Nuclear Medicine, 57(7), 1130-1135. doi:10.2967/jnumed.115.165886Yamamoto, S., Watabe, H., Kanai, Y., Watabe, T., Kato, K., & Hatazawa, J. (2013). Development of an ultrahigh resolution Si-PM based PET system for small animals. Physics in Medicine and Biology, 58(21), 7875-7888. doi:10.1088/0031-9155/58/21/7875Yang, Y., James, S. S., Wu, Y., Du, H., Qi, J., Farrell, R., … Cherry, S. R. (2010). Tapered LSO arrays for small animal PET. Physics in Medicine and Biology, 56(1), 139-153. doi:10.1088/0031-9155/56/1/009Godinez, F., Gong, K., Zhou, J., Judenhofer, M. S., Chaudhari, A. J., & Badawi, R. D. (2018). Development of an Ultra High Resolution PET Scanner for Imaging Rodent Paws: PawPET. IEEE Transactions on Radiation and Plasma Medical Sciences, 2(1), 7-16. doi:10.1109/trpms.2017.2765486Gonzalez, A. J., Aguilar, A., Conde, P., Hernandez, L., Moliner, L., Vidal, L. F., … Benlloch, J. M. (2016). A PET Design Based on SiPM and Monolithic LYSO Crystals: Performance Evaluation. IEEE Transactions on Nuclear Science, 63(5), 2471-2477. doi:10.1109/tns.2016.2522179Moses, W. W. (2011). Fundamental limits of spatial resolution in PET. 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The MINDVIEW project: First results. European Psychiatry, 50, 21-27. doi:10.1016/j.eurpsy.2018.01.002Gonzalez-Montoro, A., Benlloch, J. M., Gonzalez, A. J., Aguilar, A., Canizares, G., Conde, P., … Sanchez, F. (2017). Performance Study of a Large Monolithic LYSO PET Detector With Accurate Photon DOI Using Retroreflector Layers. IEEE Transactions on Radiation and Plasma Medical Sciences, 1(3), 229-237. doi:10.1109/trpms.2017.2692819Moliner, L., González, A. J., Soriano, A., Sánchez, F., Correcher, C., Orero, A., … Benlloch, J. M. (2012). Design and evaluation of the MAMMI dedicated breast PET. Medical Physics, 39(9), 5393-5404. doi:10.1118/1.4742850Morrocchi, M., Ambrosi, G., Bisogni, M. G., Bosi, F., Boretto, M., Cerello, P., … Del Guerra, A. (2017). Depth of interaction determination in monolithic scintillator with double side SiPM readout. EJNMMI Physics, 4(1). doi:10.1186/s40658-017-0180-9Xie, S., Zhao, Z., Yang, M., Weng, F., Huang, Q., Xu, J., & Peng, Q. (2017). LOR-PET: a novel PET camera constructed with a monolithic scintillator ring. 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC). doi:10.1109/nssmic.2017.8532627Stolin, A. V., Martone, P. F., Jaliparthi, G., & Raylman, R. R. (2017). Preclinical positron emission tomography scanner based on a monolithic annulus of scintillator: initial design study. Journal of Medical Imaging, 4(1), 011007. doi:10.1117/1.jmi.4.1.011007Gonzalez, A. J., Aguilar, A., Conde, P., Gonzalez-Montoro, A., Sanchez, S., Moliner, L., … Benlloch, J. M. (2016). Pilot tests of a PET insert based on monolithic crystals in a 7T MR. 2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop (NSS/MIC/RTSD). doi:10.1109/nssmic.2016.8069496Jan, S., Santin, G., Strul, D., Staelens, S., Assié, K., Autret, D., … Bloomfield, P. M. (2004). GATE: a simulation toolkit for PET and SPECT. 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CowN Sustains Nitrogenase Turnover in the Presence of the Inhibitor Carbon Monoxide

Nitrogenase is the only enzyme capable of catalyzing nitrogen fixation, the reduction of dinitrogen gas (N2) to ammonia (NH3). Nitrogenase is tightly inhibited by the environmental gas carbon monoxide (CO). Nitrogen-fixing bacteria rely on the protein CowN to grow in the presence of CO. However, the mechanism by which CowN operates is unknown. Here, we present the biochemical characterization of CowN and examine how CowN protects nitrogenase from CO. We determine that CowN interacts directly with nitrogenase and that CowN protection observes hyperbolic kinetics with respect to CowN concentration. At a CO concentration of 0.001 atm, CowN restores nearly full nitrogenase activity. Our results further indicate that CowN’s protection mechanism involves decreasing the binding affinity of CO to nitrogenase’s active site approximately tenfold without interrupting substrate turnover. Taken together, our work suggests CowN is an important auxiliary protein in nitrogen fixation that engenders CO tolerance to nitrogenase