Technical Educational Institute of Athens

Egaleo, Greece

Technical Educational Institute of Athens

Egaleo, Greece
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Kostou T.,University of Patras | Papadimitroulas P.,University of Patras | Loudos G.,Technical Educational Institute of Athens | Kagadis G.C.,University of Patras
Medical Physics | Year: 2013

Purpose: To develop a database of realistic animal SPECT simulations.Simulations were performed using a wholebody mouse model testing several realistic preclinical situations and compared against real small animal imaging acquisitions. Methods: The GATE Monte Carlo toolkit was used for modeling a small animal SPECT system. The camera has a hexagonal parallel hole collimator and a ∼1.6 mm spatial resolution.The 4D digital MOBY phantom was used in order to model mouse anatomy and activity distribution.Planar and SPECT scans for the biodistribution of the commonly used 99mTc based radiopharmaceuticals (MIBI, MDP and HMPAO) were modeled. Resulting simulated data were reconstructed using the QSPECT opensource software for SPECT reconstruction with a 10% energy window. Results: Simulations were executed in the GateLab grid resulting to: a) MDP bone scan biodistribution (anterior posterior planar images), b) Whole body mouse Sestamibi biodistribution, c) 99mTc HMPAO (whole body scan), d) 2 scans for HMPAO biokinetics within the brain (mouse and rat), and e) 99mTc radiolabled magnetic nanoparticles imaging with the MOBY phantom (the activity distribution was extracted from real data). Quantitative analysis was performed in several regions of interest. Simulated results were compared against real data and theoretical values available in the literature.The HMPAO brain biokinetics of both the mouse and rat brains were compared in order to investigate the impact of the brain size on detecting various brain structures.In the mouse model the brain was observed as a single entity, while in the case of the rat brain model structures were distinguished. Conclusion: GATE provides precise physics modeling based on the Geant4 code, while the 4D MOBY phantom can produce realistic imaging data, against which other imaging systems, reconstruction and correction techniques can be compared and standardized. To our knowledge this is the first small animal SPECT database with corresponding imaging data of realistic preclinical situations. © 2013, American Association of Physicists in Medicine. All rights reserved.

Karkanas P.,Ephoreia of Palaeoanthropology Speleology of Southern Greece | Pavlopoulos K.,Harokopio University | Kouli K.,National and Kapodistrian University of Athens | Ntinou M.,University of Ioannina | And 3 more authors.
Geoarchaeology | Year: 2011

Dispilio is a lakeside settlement by the Orestias Lake, Kastoria, northern Greece. The site was inhabited from the Middle Neolithic to the Chalcolithic, with some surface evidence of Bronze Age occupation. Microfacies analysis of the sediments, supported by a suite of environmental indices, has provided detailed paleoenvironmental data and elucidated the main processes involved in the formation of the site and its history of occupation. The settlement was established on the lakeshore, on a shallow sand ridge and a shore marsh. Initially, houses were built on raised platforms above the water. After a major conflagration, a range of depositional microenvironments were established that caused local changes in the sedimentation rate. Therefore, some areas quickly emerged and became dry land, while some others continued to be flooded as part of the transitional supra-littoral environment. On the dry land, houses were built directly on the ground, whereas in the transitional areas houses continued to be built on raised platforms. Thus, gradually, a mound was formed and further shaped by subsequent lake-level fluctuations. One of the lake-level rises is tentatively related to the abandonment of the mound in the Chalcolithic and the development of a hardpan on its surface. There is also evidence of later occupation during the Bronze Age in the form of a few, mostly surface, archaeological remains. © 2010 Wiley Periodicals, Inc.

Facorellis Y.,Technical Educational Institute of Athens | Karkanas P.,Ephorate of Palaeoanthropology and Speleology of Southern Greece | Higham T.,University of Oxford | Brock F.,University of Oxford | And 2 more authors.
Radiocarbon | Year: 2013

Theopetra Cave is a unique prehistoric site for Greece, as the Middle and Upper Paleolithic, Mesolithic, and Neolithic periods are present here, ridging the Pleistocene with the Holocene. During the more than 20 yr of excavation campaigns, charcoal samples from hearths suitable for 14C dating were collected from all anthropogenic layers, including the Paleolithic ones. Most of the samples were initially dated using the ABA chemical pretreatment protocol in the Laboratory of Archaeometry of NCSR Demokritos, reece, and the Radiocarbon Dating and Cosmogenic Isotopes Laboratory of the Weizmann Institute of Science, Israel. The 14C results, which were not always consistent versus depth, howed that the earliest limit of human presence is ~50,000 yr BP, thus reaching the age limits of the 14C dating method. However, 10 TL-dated burnt flint specimens unearthed from the lower part of the Middle Paleolithic sequence of the cave gave ages ranging between ~110 and 135 kyr ago. hese results are in disagreement with the 14C dates, as they support a much later date for these layers. n order to clarify the situation further, charcoal samples originating from hearths were conventionally dated in the Laboratory of Archaeometry of NCSR Demokritos using the ABA pretreatment. dditionally, hand-picked charcoal fragments also underwent 14C dating by AMS in the Oxford Radiocarbon Accelerator Unit using the acid-base wet oxidation (ABOX-SC) pretreatment protocol. The 14C dates from the cave's Paleolithic layers obtained by both pretreatment protocols suggest a probable charcoal diagenesis affecting the 14C results of these very old samples. However, the dates obtained with ABOX-SC pretreatment are considered more reliable and in the younger stratigraphic part produced consistent results with the TL dating. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.

Facorellis Y.,Technical Educational Institute of Athens | Coleman J.E.,Cornell University
Radiocarbon | Year: 2012

Archaeological investigations at Halai, a small city-state on the sea coast of East Lokris in Greece, have been carried out since 1986 by the Cornell Halai and East Lokris Project (CHELP). The town's acropolis, first inhabited in the Neolithic period, was in Greco-Roman times a political and cultural center controlling and serving a considerable territory. Radiocarbon dating of charred material unearthed from Neolithic deposits indicate that the Neolithic occupation probably lasted from about 6000 to 5300 BC. Details of dating are somewhat problematic, however, because of outlying determinations and lack of close agreement between determinations from the same or stratigraphically comparable material. © 2012 by the Arizona Board of Regents on behalf of the University of Arizona.

Efthimiou N.,University of Patras | Loudos G.,Technical Educational Institute of Athens | Karakatsanis N.A.,Johns Hopkins University | Panayiotakis G.S.,University of Patras
Medical Physics | Year: 2013

Purpose: In this work, the authors aim for the estimation of the effect of 176Lu intrinsic radioactivity on the performance of a dual head PET system dedicated to small animal imaging. Methods: A prototype camera has been used as a reference system in order to validate two GATE simulation models, which were used for the investigation. The first model includes the 176Lu intrinsic radioactivity, while the second does not. The two models have been designed in order to provide similar sensitivities, in terms of count rate performance and scatter fraction, in the linear range of activities. In addition, the model with the 176Lu intrinsic radioactivity, has been validated in terms of background count rate. Different acquisition schemes have been examined in order to determine the optimum conditions to minimize the 176Lu effects, while maintaining a high trues count rate. In addition, the effect on the image quality, in terms of spatial resolution, signal-to-noise ratio, and minimum detectable activity, was investigated. Results: Both models are in good agreement with the measured data. While, the presence of the 176Lu altered the dead time of the model, it also affected the singles, trues, and randoms count rates. The noise equivalent count rate curves of the two models indicate that for low activities, the lack of 176Lu radioactivity leads to better noise properties due to the underestimation of the randoms. Signal-to-noise ratio measurement on coincidence images confirm the aforementioned claim, since the model without the 176Lu provides better less noisy images. Furthermore, the spatial resolution and the minimum detectable activity are overestimated. Conclusions: It has been proven that the lack of the 176Lu intrinsic radioactivity has an impact on the design of the simulation model's dead time. Even if there is an alignment with experimental results still the noise properties, for a wide range of activities, are overestimated. In addition, for low activities, better image quality, is presented, mainly due to the lack of the 176Lu photons which blur the images. Furthermore, it was shown that the use of a high hardware threshold allows the application of a wide energy window, which improves the statistics without a significant compromise on the quality of the detected photons, mainly, due to the early rejection of the low energy photons and the low scatter factor. © 2013 American Association of Physicists in Medicine.

Commonly used radiopharmaceuticals were tested to define the most important dosimetric factors in preclinical studies. Dosimetric calculations were applied in two different whole-body mouse models, with varying organ size, so as to determine their impact on absorbed doses and S-values. Organ mass influence was evaluated with computational models and Monte Carlo(MC) simulations.MC simulations were executed on GATE to determine dose distribution in the 4D digital MOBY mouse phantom. Two mouse models, 28 and 34 g respectively, were constructed based on realistic preclinical exams to calculate the absorbed doses and S-values of five commonly used radionuclides in SPECT/PET studies (18F, 68Ga, 177Lu, 111In and 99mTc).Radionuclide biodistributions were obtained from literature. Realistic statistics (uncertainty lower than 4.5%) were acquired using the standard physical model in Geant4. Comparisons of the dosimetric calculations on the two different phantoms for each radiopharmaceutical are presented.Dose per organ in mGy was calculated for all radiopharmaceuticals. The two models introduced a difference of 0.69% in their brain masses, while the largest differences were observed in the marrow 18.98% and in the thyroid 18.65% masses.Furthermore, S-values of the most important target-organs were calculated for each isotope. Source-organ was selected to be the whole mouse body.Differences on the S-factors were observed in the 6.0-30.0% range. Tables with all the calculations as reference dosimetric data were developed.Accurate dose per organ and the most appropriate S-values are derived for specific preclinical studies. The impact of the mouse model size is rather high (up to 30% for a 17.65% difference in the total mass), and thus accurate definition of the organ mass is a crucial parameter for self-absorbed S values calculation.Our goal is to extent the study for accurate estimations in small animal imaging, whereas it is known that there is a large variety in the anatomy of the organs.

PubMed | Technical Educational Institute of Athens and University of Patras
Type: Journal Article | Journal: Medical physics | Year: 2016

Our purpose is to evaluate the administered absorbed dose in pediatric, nuclear imaging studies. Monte Carlo simulations with the incorporation of pediatric computational models can serve as reference for the accurate determination of absorbed dose. The procedure of the calculated dosimetric factors is described, while a dataset of reference doses is created.Realistic simulations were executed using the GATE toolkit and a series of pediatric computational models, developed by the IT IS Foundation. The series of the phantoms used in our work includes 6 models in the range of 5-14 years old (3 boys and 3 girls). Pre-processing techniques were applied to the images, to incorporate the phantoms in GATE simulations. The resolution of the phantoms was set to 2 mm3. The most important organ densities were simulated according to the GATE Materials Database. Several used radiopharmaceuticals in SPECT and PET applications are being tested, following the EANM pediatric dosage protocol. The biodistributions of the several isotopes used as activity maps in the simulations, were derived by the literature.Initial results of absorbed dose per organ (mGy) are presented in a 5 years old girl from the whole body exposure to 99mTc - SestaMIBI, 30 minutes after administration. Heart, kidney, liver, ovary, pancreas and brain are the most critical organs, in which the S-factors are calculated. The statistical uncertainty in the simulation procedure was kept lower than 5%. The Sfactors for each target organ are calculated in Gy/(MBq*sec) with highest dose being absorbed in kidneys and pancreas (9.29*10An approach for the accurate dosimetry on pediatric models is presented, creating a reference dosage dataset for several radionuclides in children computational models with the advantages of MC techniques. Our study is ongoing, extending our investigation to other reference models and evaluating the results with clinical estimated doses.

Fylladitakis E.D.,Brunel University | Theodoridis M.P.,Brunel University | Moronis A.X.,Technical Educational Institute of Athens
IEEE Transactions on Plasma Science | Year: 2014

Corona discharge refers to the phenomenon when the electric field near a conductor is strong enough to ionize the dielectric surrounding it but not strong enough to cause an electrical breakdown or arcing between conductors or other components. This phenomenon is unwanted and dangerous in high-voltage systems; however, a controlled corona discharge may be used to ionize a fluid and induce motion by directly converting the electrical energy into kinetic energy. Phenomena that involve the direct conversion of electrical energy into kinetic energy are known as electrohydrodynamic (EHD) and have a variety of possible applications today. This paper contains a literature review of the research regarding the EHD effects associated with corona discharges, from the first observation of the phenomenon to the most recent advancements on its mathematical modeling, as well as the advancements on specific applications, such as thrust, heat transfer improvement, boundary layer enhancement, drying, fluid pumping, and cooling. © 2013 IEEE.

Tang J.,National Technical University of Athens | Tang J.,North University of China | Photopoulos P.,National Technical University of Athens | Photopoulos P.,Technical Educational Institute of Athens | And 3 more authors.
Nanotechnology | Year: 2011

In this work, a novel Ag nanoparticle self-assembly process based on plasma-induced two-dimensional Ostwald ripening is demonstrated. Ag nanoparticles are deposited on p-doped Si substrates using a DC magnetron sputtering process. With the assistance of O2/Ar plasma treatment, different sizes and patterns of Ag nanoparticles are formed, due to the Ostwald ripening. The evolution of plasma-induced nanoparticle ripening is studied and a clear increase in particle size and a decrease in particle density are observed with increasing plasma treatment. From the experiments, it is concluded that the initial nanoparticle density and the plasma gas mixture (Ar/O2 ratio) are important factors that affect the ripening process. The proposed plasma-directed Ag nanoparticle self-assembly provides a rapid method of tailoring the nanoparticle distribution on substrates, with potential applications in the fields of solar cells, biosensors, and catalysis. © 2011 IOP Publishing Ltd.

Galanis G.,Hellenic Naval Academy | Famelis I.,Technical Educational Institute of Athens | Liakatas A.,Hellenic Naval Academy
Stochastic Environmental Research and Risk Assessment | Year: 2016

A new Kalman filter is presented in this work, enhanced with abilities and tools obtained from the area of Information Geometry (IG), for the optimization of the results of numerical weather prediction models. The new developments allow the better estimation of the discrepancies between modeled and corresponding observed data sets by categorizing them in the appropriate geometric framework and utilizing the associated geodesics/minimum-length-curves in order to estimate and minimize the necessary cost functions, instead of adopting least square based approximations. Numerical analysis techniques are developed and used for solving the associated boundary value problems. The proposed new IG Kalman filter is evaluated over idealized and real world test cases with very promising results. The systematic error of the simulations is almost eliminated and the forecast uncertainty is critically reduced. © 2016 Springer-Verlag Berlin Heidelberg

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