Letteratura scientifica selezionata sul tema "Imagerie 3-Gamma"
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Articoli di riviste sul tema "Imagerie 3-Gamma"
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Liu, Xiao, Hui Liu, Li Cheng, Jing Wu, Tianwei Bao, Rutao Yao e Yaqiang Liu. "A 3-dimensional stationary cascade gamma-ray coincidence imager". Physics in Medicine & Biology 66, n. 22 (5 novembre 2021): 225001. http://dx.doi.org/10.1088/1361-6560/ac311b.
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Adugna, Tesfaye, Wenbo Xu e Jinlong Fan. "Comparison of Random Forest and Support Vector Machine Classifiers for Regional Land Cover Mapping Using Coarse Resolution FY-3C Images". Remote Sensing 14, n. 3 (25 gennaio 2022): 574. http://dx.doi.org/10.3390/rs14030574.
Testo completoAbstract (sommario):
The type of algorithm employed to classify remote sensing imageries plays a great role in affecting the accuracy. In recent decades, machine learning (ML) has received great attention due to its robustness in remote sensing image classification. In this regard, random forest (RF) and support vector machine (SVM) are two of the most widely used ML algorithms to generate land cover (LC) maps from satellite imageries. Although several comparisons have been conducted between these two algorithms, the findings are contradicting. Moreover, the comparisons were made on local-scale LC map generation either from high or medium resolution images using various software, but not Python. In this paper, we compared the performance of these two algorithms for large area LC mapping of parts of Africa using coarse resolution imageries in the Python platform by the employing Scikit-Learn (sklearn) library. We employed a big dataset, 297 metrics, comprised of systematically selected 9-month composite FegnYun-3C (FY-3C) satellite images with 1 km resolution. Several experiments were performed using a range of values to determine the best values for the two most important parameters of each classifier, the number of trees and the number of variables, for RF, and penalty value and gamma for SVM, and to obtain the best model of each algorithm. Our results showed that RF outperformed SVM yielding 0.86 (OA) and 0.83 (k), which are 1–2% and 3% higher than the best SVM model, respectively. In addition, RF performed better in mixed class classification; however, it performed almost the same when classifying relatively pure classes with distinct spectral variation, i.e., consisting of less mixed pixels. Furthermore, RF is more efficient in handling large input datasets where the SVM fails. Hence, RF is a more robust ML algorithm especially for heterogeneous large area mapping using coarse resolution images. Finally, default parameter values in the sklearn library work well for satellite image classification with minor/or no adjustment for these algorithms.
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Lee, Wonho, Ajin Jo e Changyeon Yoon. "Multiple Modality $\gamma$-Ray Imager Using LaCl$_{3}$(Ce) Scintillators With Active Collimation Method". IEEE Transactions on Nuclear Science 57, n. 3 (giugno 2010): 1396–403. http://dx.doi.org/10.1109/tns.2010.2043539.
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Sekandari, Milad, e Amin Beiranvand Pour. "Fuzzy Logic Modeling for Integrating the Thematic Layers Derived from Remote Sensing Imagery: A Mineral Exploration Technique". Environmental Sciences Proceedings 6, n. 1 (25 febbraio 2021): 8. http://dx.doi.org/10.3390/iecms2021-09349.
Testo completoAbstract (sommario):
In this study, fuzzy logic modeling was implemented to fuse the thematic layers derived from principal components analysis (PCA) in order to generate mineral prospectivity maps. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and WorldView-3 (WV-3) satellite remote sensing data were used. A spatial subset zone of the Central Iranian Terrane (CIT), Iran was selected in this study. The PCA technique was implemented for the processing of the datasets and for the production of alteration thematic layers. PCA4, PCA5, and PCA8 were selected as the most rational alteration thematic layers of ASTER for the generation of a prospectivity map. The fuzzy gamma operator was used to fuse the selected alteration thematic layers. The PCA3, PCA4, and PCA6 thematic layers (most rational alteration thematic layers) of WV-3 were fused using the fuzzy AND operator. Field reconnaissance, X-ray diffraction (XRD) analysis, and Analytical Spectral Devices (ASD) spectroscopy were carried out to verify the image processing results. Subsequently, mineral prospectivity maps were produced showing high-potential zones of Pb-Zn mineralization in the study area.
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Cona, Filippo, Melissa Zavaglia, Laura Astolfi, Fabio Babiloni e Mauro Ursino. "Changes in EEG Power Spectral Density and Cortical Connectivity in Healthy and Tetraplegic Patients during a Motor Imagery Task". Computational Intelligence and Neuroscience 2009 (2009): 1–12. http://dx.doi.org/10.1155/2009/279515.
Testo completoAbstract (sommario):
Knowledge of brain connectivity is an important aspect of modern neuroscience, to understand how the brain realizes its functions. In this work, neural mass models including four groups of excitatory and inhibitory neurons are used to estimate the connectivity among three cortical regions of interests (ROIs) during a foot-movement task. Real data were obtained via high-resolution scalp EEGs on two populations: healthy volunteers and tetraplegic patients. A 3-shell Boundary Element Model of the head was used to estimate the cortical current density and to derive cortical EEGs in the three ROIs. The model assumes that each ROI can generate an intrinsic rhythm in the beta range, and receives rhythms in the alpha and gamma ranges from other two regions. Connectivity strengths among the ROIs were estimated by means of an original genetic algorithm that tries to minimize several cost functions of the difference between real and model power spectral densities. Results show that the stronger connections are those from the cingulate cortex to the primary and supplementary motor areas, thus emphasizing the pivotal role played by theCMA_Lduring the task. Tetraplegic patients exhibit higher connectivity strength on average, with significant statistical differences in some connections. The results are commented and virtues and limitations of the proposed method discussed.
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Kitayama, Yoshiharu, Mitsuhiro Nogami e Keitaro Hitomi. "An experimental feasibility study of a 4π gamma-ray imager using detector response patterns". Japanese Journal of Applied Physics, 25 giugno 2024. http://dx.doi.org/10.35848/1347-4065/ad5ba0.
Testo completoAbstract (sommario):
Abstract We constructed a gamma-ray imager that estimates the distribution of gamma-ray sources based on the response patterns of multiple gamma-ray detectors randomly positioned in three-dimensional space. The Coded Cube Camera for Gamma-ray (C3G), comprising eight GAGG (Ce) scintillator and eighteen lead cubes is housed in a cubical casing with an 86 mm edge length and weighs approximately 600 g. The results of the 4π imaging experiment confirmed the feasibility of imaging a 10 MBq 137Cs source 3 m away for a 10 min measurement. C3G operates with only eight channels, instead of the hundreds needed by a typical imager. This setup allows for a simplified circuit and reconstruction algorithm, resulting in a cost-effective and reliable system. With its compact and lightweight design and 4π field of view, this technology is expected to find extensive applications in astronomy, medicine, nuclear security, and decommissioning projects.
Tesi sul tema "Imagerie 3-Gamma"
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Paradiso, Vincenzo. "Development of a portable gamma camera for accurate 3-D localization of radioactive hotspots". Thesis, Normandie, 2017. http://www.theses.fr/2017NORMC209.
Testo completoAbstract (sommario):
Le présent travail a pour but le développement d’une caméra gamma à masque codé permettant d’estimer la position tridimensionnelle (3D) des sources radioactives. Cela est d’un intérêt considérable dans le cadre d’un grand nombre d'applications, de la reconstruction de la forme 3D des objets radioactifs aux systèmes de réalité augmentée appliqués à la radioprotection. Les caméras gamma portables actuelles ne fournissent que la position angulaire relative des sources gamma à localiser, c'est-à-dire qu'aucune information métrique concernant les sources n’est disponible, comme par exemple leur distance par rapport à la caméra. Dans cette thèse, nous proposons principalement deux approches permettant d’estimer la position 3D des sources. La première approche consiste à étalonner la caméra gamma avec un capteur de profondeur à lumière structurée. La seconde approche permet d'estimer la distance source-détecteur par une méthode d’imagerie gamma stéréoscopique. Pour aligner géométriquement les images obtenues par la caméra gamma, le capteur de profondeur, et la caméra optique, une procédure d'étalonnage n’utilisant qu’une seule source ponctuelle radioactive a été conçue et mise en œuvre. Les résultats expérimentaux démontrent que les approches proposées permettent d'obtenir une précision inférieure au pixel, tant pour l’erreur de reprojection que pour la superposition des images gamma et optiques. Ces travaux présentent également une analyse quantitative de la précision et de la résolution relatives à l’estimation de la distance source-détecteur. De plus, les résultats obtenus ont validé le choix de la géométrie du modèle sténopé pour les caméras gamma à masque codéA coded aperture gamma camera for retrieving the three-dimensional (3-D) position of radioactive sources is presented. This is of considerable interest for a wide number of applications, ranging from the reconstruction of the 3-D shape of radioactive objects to augmented reality systems. Current portable γ-cameras only provide the relative angular position of the hotspots within their field of view. That is, they do not provide any metric information concerning the located sources. In this study, we propose two approaches to estimate the distance of the surrounding hotspots, and to autonomously determine if they are occluded by an object. The first consists in combining and accurately calibrating the gamma camera with a structured-light depth sensor. The second approach allows the estimation of the source-detector distance by means of stereo gamma imaging. To geometrically align the images obtained by the gamma, depth, and optical cameras used, a versatile calibration procedure has been designed and carried out. Such procedure uses a calibration phantom intentionally easy to build and inexpensive, allowing the procedure to be performed with only one radioactive point source. Experimental results showed that our calibration procedure yields to sub-pixel accuracy both in the re-projection error and the overlay of radiation and optical images. A quantitative analysis concerning the accuracy and resolution of the retrieved source-detector distance is also provided, along with an insight into the respective most influential factors. Moreover, the results obtained validated the choice of the geometry of the pinhole model for a coded aperture gamma camera
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Cai, Dingbang. "Contributions to instrumental developments for the XEMIS2 camera, on-board ionization and scintillation measurements". Electronic Thesis or Diss., Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2024. http://www.theses.fr/2024IMTA0408.
Testo completoAbstract (sommario):
Les travaux décrits dans cette thèse sont centrés sur l'évolution de l'imagerie médicale nucléaire, des techniques d'imagerie fondamentales aux innovations actuelles, avec un focus particulier sur la caméra XEMIS2. Cette caméra Compton au xénon liquide est conçue pour l'imagerie 3-gamma des petits animaux à faible activité. L'objectif principal de XEMIS2 est de localiser en trois dimensions un radiopharmaceutique marqué avec un radionucléide spécifique, tel que le Scandium-44, tout en réduisant l'activité administrée sans compromettre la qualité de l'image.La thèse se concentre ensuite sur le développement et les performances de la caméra XEMIS2. Elle couvre les principes opérationnels des chambres de projection temporelle au xénon liquide (LXeTPCs), l'utilisation de la grille de Frisch pour améliorer les performances des chambres d'ionisation, et le processus complexe de la calibration des signaux de scintillation dans XEMIS2 en utilisant la méthode Time over Threshold (TOT). Les efforts d'optimisation des résultats de calibration sont également abordés. En résumant ces avancées technologiques et méthodologiques, la thèse offre une perspective historique et une analyse prospective des impacts potentiels de ces technologies sur les diagnostics médicaux et la rechercheThe work described in this thesis focuses on the evolution of nuclear medical imaging, from fundamental imaging techniques to current innovations, with a particular focus on the XEMIS2 camera. This liquid xenon Compton camera is designed for 3-gamma imaging of small, low-activity animals. The main objective of XEMIS2 is to localize in three dimensions a radiopharmaceutical labeled with a specific radionuclide, such as Scandium-44, while reducing the administered activity without compromising image quality. The thesis then focuses on the development and performance of the XEMIS2 camera. It covers the operational principles of the liquid xenon time projection chambers (LXeTPCs), the use of the Frisch grid to improve the performance of the ionization chambers, and the complex process of calibrating the scintillation signals in XEMIS2 using the Time over Threshold (TOT) method. Efforts to optimize calibration results are also discussed. By summarizing these technological and methodological advances, the thesis provides a historical perspective and a prospective analysis of the potential impact of these technologies on medical diagnostics and research
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Duval, Samuel. "Développement d'un photomultiplicateur gazeux cryogénique dédié à un télescope Compton au xénon liquide pour l'imagerie médicale". Phd thesis, Université de Nantes, 2010. http://tel.archives-ouvertes.fr/tel-00594636.
Testo completoAbstract (sommario):
Une technique d'imagerie innovante reposant sur la localisation tridimensionnelle d'un radioisotope émetteur (bêta, gamma) à l'aide d'un télescope Compton au xénon liquide a été proposée au laboratoire SUBATECH en 2003. Cette technique, appelée imagerie 3 gammas, repose sur l'association d'une caméra à tomographie d'émission de positons pour la reconstruction des deux photons d'annihilation et d'une chambre à projection temporelle au xénon liquide pour la reconstruction du troisième photon. L'interaction de ce dernier avec le xénon liquide induit un signal de scintillation, lu avec un tube photomultiplicateur, qui permet de déclencher l'acquisition du signal d'ionisation, lu avec un MICROMEGAS (MICRO MEsh Gaseous Structure), donnant accès à la mesure de l'énergie et de la position de chaque interaction. Dans le cadre de ce développement, nous proposons une alternative à la lecture du signal de scintillation avec des tubes photomultiplicateurs classiques : un photomultiplicateur gazeux cryogénique de large surface. Ce photodétecteur est doté d'une photocathode réflective solide d'iodure de césium pour la photoconversion des photons UV et de microstructures amplificatrices telles que le THGEM (THick Gaseous Electron Multiplier), le MICROMEGAS et le PIM (Parallel Ionization Multiplier). Il devrait permettre une segmentation virtuelle du volume de xénon liquide afin de réduire l'occupation du télescope. Les premiers résultats obtenus à l'aide d'un premier prototype de petite surface à la température du xénon liquide (173 K) sont présentés.
Atti di convegni sul tema "Imagerie 3-Gamma"
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Du, Yanfeng, Wen Li, Brian Yanoff, Jeffrey Gordon e Donald Castleberry. "4 pi direction sensitive gamma imager with RENA-3 readout ASIC". In Optical Engineering + Applications, a cura di Ralph B. James, Arnold Burger e Larry A. Franks. SPIE, 2007. http://dx.doi.org/10.1117/12.739073.
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Takeda, Shin'ichiro, Tadayuki Takahashi, Shin-nosuke Ishikawa, Hirokazu Odaka, Shin Watanabe, Hiroyasu Tajima, Naoki Kawachi e Takashi Nakano. "Simulation study of 3-D gamma-ray imager with Si/CdTe semiconductor Compton camera". In 2010 IEEE Sensors Applications Symposium (SAS). IEEE, 2010. http://dx.doi.org/10.1109/sas.2010.5439430.
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Langford, Cory, Medhat Mickael e Craig Barnett. "A Compact Multisensor LWD Tool Optimized for Unconventional Reservoirs". In 2023 SPWLA 64th Annual Logging Symposium. Society of Petrophysicists and Well Log Analysts, 2023. http://dx.doi.org/10.30632/spwla-2023-0103.
Testo completoAbstract (sommario):
High-cost deepwater, high-pressure/high-temperature (HP/HT), and extended-reach wells in conventional reservoirs drove impressive developments in logging-while-drilling (LWD) technology in recent decades. However, the length, cost, and mechanical specifications of traditional LWD tools make them generally unattractive for use in onshore unconventional reservoirs, which present very different economic and technical challenges. This has led to the development of a compact integrated LWD tool optimized for geosteering, evaluating, and optimally completing unconventional reservoirs. Azimuthal spectral gamma ray, high-resolution ultrasonic imaging, and azimuthal sonic sensors are incorporated into a single 14.5-ft (4.4 m) sensor collar. Applications of the azimuthal spectral gamma ray sensor include real-time geosteering, organic content evaluation, and clay content determination in uranium-bearing shales and carbonates. The ultrasonic imager provides high-resolution borehole images in both water-based and oil-based muds for fracture and fault detection, stress orientation, formation dip, and borehole stability applications. The ultrasonic imager also provides high-resolution caliper data. Azimuthally oriented compressional and shear slowness measurements from the azimuthal unipole sonic sensor provide important geomechanical, geophysical, and petrophysical information, including Poisson’s ratio, porosity, and VTI shear anisotropy in horizontal wells. Log examples from various North American basins demonstrate the applications of this integrated LWD logging suite. Spectral gamma ray data from the Marcellus Shale differentiates high clay formations from cleaner, organic-rich, uranium-bearing formations, facilitating the evaluation of both organic content and clay content from K, U, and Th data. Ultrasonic imager data from the Marcellus Shale and Permian Basin reveal natural fractures and formation dip, as well as borehole breakout in both normal and thrust fault stress regimes. Azimuthally focused unipole array sonic measurements from a horizontal well in the Wolfcamp Formation resolve intrinsic VTI anisotropy. Together, these measurements allow operators to locate and geosteer in unconventional strata with higher organic content and/or geomechanical properties, which are more conducive to hydraulic fracturing. These measurements also facilitate engineered completions, where frac stages are selectively placed to group together rocks with similar mechanical properties in each individual stage. Incorporating multiple logging sensors with particular value for unconventional reservoirs into a single compact drill collar represents a new direction in LWD technology. In addition to the primary drilling and evaluation applications, recent log data have also revealed several novel uses, including (1) observing the early time progression of borehole breakout by comparing ultrasonic images acquired while drilling and shortly after drilling, (2) detecting gas influx while drilling from decreases in ultrasonic imager amplitude, and (3) monitoring significant variations in mud slowness during various drilling operations using the ultrasonic mud cell. This integrated logging suite has also found applications beyond unconventional reservoirs, including use in fractured granite geothermal drilling and, when combined with LWD resistivity, in conventional offshore wells.
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Fares, Wael, Swapan Dey, Paul New, Warda Albreiki, Atiqurrahman Bin Abd Rashid, Gabriela Lopez, Ahmed Ghobashy, Muhammad Mubeen e Nigel Clegg. "Developing Carbonate Low Resistivity Pay Using Advanced LWD Ultra-Deep Resistivity with Nuclear Magnetic Resonance and High-Resolution Micro-Resistivity Imaging, A Case Study in a Mature Field, Onshore Abu Dhabi". In ADIPEC. SPE, 2023. http://dx.doi.org/10.2118/216744-ms.
Testo completoAbstract (sommario):
Abstract One of the major challenges in low resistivity pay zones (below 1 ohm.m) is to map the surrounding boundaries and the reservoir thickness. This has a significant impact on the understanding of the subsequent hydrocarbon production. This case study presents an effective approach in two recent wells where effective well placement and formation evaluation were achieved using Multiple Logging While Drilling (LWD) sensors, including Ultra-Deep Azimuthal Resistivity (UDAR) mapping technology in low resistivity carbonate zone. Extensive pre-well modeling analysis performed for both wells using all available nearby offset wells has concluded that the UDAR technology would be sensitive enough to identify the low resistivity zones in two 6-in. laterals in two wells. In Well 1, 4 ¾-in. Gamma Ray, Wave Propagation Resistivity, Density/Neutron and UDAR Logging-While-Drilling (LWD) sensors were used to drill approximately 3,200 feet. Well 2 was planned as a 6-in. lateral with Maximum Reservoir Contact (MRC) up to 8,466 feet, intersecting two carbonate layers. The Bottom Hole Assembly (BHA) included an even larger suite of LWD sensors, comprising UDAR, Gamma Ray, Wave Propagation Resistivity, Laterolog Micro-Resistivity Imager, Density/Neutron and Nuclear Magnetic Resonance (NMR). 1-Dimensional (1D) and 3-Dimensional (3D) inversions of the UDAR data in real-time allowed a precise mapping of formations and fluid boundaries at great distance from the wellbore. Wells 1 and 2 were drilled successfully through their respective defined target zones. In Well 1, the UDAR 1D inversion identified and confirmed the low resistivity zone below the trajectory and helped to keep the well in target zone till well TD. In Well 2, the UDAR real-time 1D and 3D inversions assisted in precisely mapping complex carbonate reservoir boundaries. Furthermore, the integration of the UDAR 1D and 3D mapping with the NMR measurements allowed identifying the bound water intervals and the direction. In addition, Laterolog Micro-Resistivity Imaging confirmed the presence of vugs and fractures along the wellbore. While moving up to the second target layer, the UDAR 1D inversion successfully mapped the reservoir boundaries, despite the low resistivity of the reservoir (0.7 – 1 Ohm.m). The array of resistivity sensors provided real-time information on the oil saturation, which helped in maximizing reservoir contact by placing the well strategically. Furthermore, the improved reservoir understanding, and insight provided by the integration of UDAR for boundary mapping, NMR for permeability and porosity readings, and Micro-Resistivity Imaging for aperture identifications assisted in optimizing the completion design to isolate unproductive intervals along the well path and delay possible water influx. Successful placement of these laterals in the productive zones despite the low resistivity normally limiting formation and boundary detection brought increased reservoir understanding and optimization of the completion design, confirming the LWD solution adequacy for such environment.
Rapporti di organizzazioni sul tema "Imagerie 3-Gamma"
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Zhong He, David Whe e Glenn Knoll. Development of Gamma-Ray Compton Imager Using Room-Temperature 3-D Position Sensitive Semiconductor Detectors. Office of Scientific and Technical Information (OSTI), maggio 2003. http://dx.doi.org/10.2172/812020.
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