Evaluation of spacial resolution of a PET scanner through the simulation and experimental measurement of the Recovery coefficient

Purpose: In order to measure spatial resolution of a PET tomograph in clinical conditions, this study describes and validates a method based on the recovery coefficient, a factor required to compensate underestimation in measured radioactivity concentration for small structures. Methods: In a PET image, the recovery factors of radioactive spheres were measured and their comparison with simulated recovery coefficients yielded the tomographic spatial resolution. Following this methodology, resolution was determined in different surrounding media and several conditions for reconstruction, including clinical conditions for brain PET studies. All spatial resolution values were compared with those obtained using classical methods with point and line sources. Results: In each considered condition, spatial resolution of the PET image estimated using the recovery coefficient showed good agreement with classical methods measurements, validating the procedure. Conclusion: Measurement of the recovery coefficient provides an assessment of tomographic spatial resolution, particularly in clinical studies conditions

The correlation between C/O ratio, metallicity and the initial WD mass for SNe Ia

In this paper, we want to check whether or not the carbon abundance can be affected by initial metallicity. We calculated a series of stellar evolution. We found that when $Z\leq0.02$, the carbon abundance is almost independent of metallicity if it is plotted against the initial WD mass. However, when $Z>0.02$, the carbon abundance is not only a function of the initial WD mass, but also metallicity, i.e. for a given initial WD mass, the higher the metallicity, the lower the carbon abundance. Based on some previous studies, i.e. both a high metallicity and a low carbon abundance lead to a lower production of $^{\rm 56}$Ni formed during SN Ia explosion, the effects of the carbon abundance and the metallicity on the amount of $^{\rm 56}$Ni are enhanced by each other, which may account for the variation of maximum luminosity of SNe Ia, at least qualitatively. Considering that the central density of WD before supernova explosion may also play a role on the production of $^{\rm 56}$Ni and the carbon abundance, the metallicity and the central density are all determined by the initial parameters of progenitor system, i.e. the initial WD mass, metallicity, orbital period and secondary mass, the amount of $^{\rm 56}$Ni might be a function of the initial parameters. Then, our results might construct a bridge linking the progenitor model and the explosion model of SNe Ia.Comment: 7pages, 4 figures, accepted for publication in A&

Tomografía por emisión de positrones en el cáncer de mama

PET18FDG is an imaging diagnostic technique that shows changes in glycolitic metabolism that appear at a very early phases in the tumoral process. The main limitation of PET in breast cancer is the detection of small tumor lesions and axillary micrometastases. However it offers important information in the staging of high risk patients, in clinical relapse or in therapeutic evaluation. The new PET-CT devices offer advantages over conventional techniques. It provides a greater precision in the localization of tumoral foci. In spite of current difficulties for clinical applications, fluoro-estradiol (18F-ES) offers the possibilty of studying the presence of estrogenic receptors both in the primary and in the metastases. It may prove to be a useful tool to obtain information about therapeutic management and prognosis of breast cancer

Effects of an exercise program on hepatic metabolism, hepatic fat, and cardiovascular health in overweight/obese adolescents from Bogotá, Colombia (the HEPAFIT study): study protocol for a randomized controlled trial

Background: A considerable proportion of contemporary youth have a high risk of obesity-related disorders such as cardiovascular disease, metabolic syndrome, or non-alcoholic fatty liver disease (NAFLD). Although there is consistent evidence for the positive effects of physical activity on several health aspects, most adolescents in Colombia are sedentary. It is, therefore, important to implement strategies that generate changes in lifestyle. The HEPAFIT study aims to examine whether a 6-month exercise program has benefits for hepatic fat content and cardiovascular health outcomes among overweight/obese adolescents from Bogotá, Colombia. Methods/design: Altogether, 100 hundred overweight/obese, sedentary adolescents (aged 11–17 years) attending two public schools in Bogotá, Colombia, will be included in a parallel-group randomized controlled trial. Adolescents will be randomly assigned to an intervention group following one of four curricula: (1) the standard physical education curriculum (60 min per week of physical activity, n = 25) at low-to-moderate intensity; (2) a high-intensity physical education curriculum (HIPE, n = 25), consisting of endurance and resistance games and non-competitive activities, such as running, gymkhanas, lifting, pushing, wrestling, or hauling, for 60-min sessions, three times per week, with an energy expenditure goal of 300 to 500 kcal/session at 75–85% maximum heart rate (HRmax); (3) a low-to-moderate intensity physical education curriculum (LIPE, n = 25) consisting of endurance and resistance games and non-competitive activities (e.g., chasing, sprinting, dribbling, or hopping) for 60-min sessions, three times per week with an energy expenditure goal of 300 kcal/session at 55–75% HRmax; and (4) a combined HIPE and LIPE curriculum (n = 25). The HIPE, LIPE, and combined interventions were performed in addition to the standard physical education curriculum. The primary outcome for effectiveness is liver fat content, as measured by the controlled attenuation parameter 1 week after the end of the intervention program. Discussion: The translational focus may be suitable for collecting new information in a school setting on the possible effects of physical activity interventions to reduce liver fat content and to improve metabolic profiles and the cardiometabolic health of overweight/obese adolescents. This may lead to the more efficient use of school physical education resources.The HEPAFIT study was carried out with the financial support of Instituto Colombiano para el Desarrollo de la Ciencia y la Tecnología “Francisco José de Caldas” COLCIENCIAS (code 59700 and no 122277757900). Katherine González-Ruíz receive a scholarship from Universidad del Rosario, Colombia, Escuela de Medicina y Ciencias de la Salud, to do a Doctorate. This article presents independent research commissioned by COLCIENCIAS under its Program Grants for Applied Research funding scheme (Convocatoria 777–2017)

Optical and IR observations of SN 2002dj: some possible common properties of fast expanding SNe Ia

As part of the European Supernova Collaboration we obtained extensive photometry and spectroscopy of the type Ia SN 2002dj covering epochs from 11 days before to nearly two years after maximum. Detailed optical and near-infrared observations show that this object belongs to the class of the high-velocity gradient events as indicated by Si, S and Ca lines. The light curve shape and velocity evolution of SN 2002dj appear to be nearly identical to SN 2002bo. The only significant difference is observed in the optical to near-IR colours and a reduced spectral emission beyond 6500 A. For high-velocity gradient Type Ia supernovae, we tentatively identify a faster rise to maximum, a more pronounced inflection in the V and R light curves after maximum and a brighter, slower declining late-time B light curve as common photometric properties of this class of objects. They also seem to be characterized by a different colour and colour evolution with respect to ``normal'' SNe Ia. The usual light curve shape parameters do not distinguish these events. Stronger, more blueshifted absorption features of intermediate-mass elements and lower temperatures are the most prominent spectroscopic features of Type Ia supernovae displaying high velocity gradients. It appears that these events burn more intermediate-mass elements in the outer layers. Possible connections to the metallicity of the progenitor star are explored.Comment: Equations A4, A5 and A7 in the appendix section have been corrected. Part of text in the appendix has been remove

Investigation of the Pu 240 (n,f) reaction at the n_TOF/EAR2 facility in the 9 meV-6 MeV range

Background: Nuclear waste management is considered amongst the major challenges in the field of nuclear energy. A possible means of addressing this issue is waste transmutation in advanced nuclear systems, whose operation requires a fast neutron spectrum. In this regard, the accurate knowledge of neutron-induced reaction cross sections of several (minor) actinide isotopes is essential for design optimization and improvement of safety margins of such systems. One such case is Pu240, due to its accumulation in spent nuclear fuel of thermal reactors and its usage in fast reactor fuel. The measurement of the Pu240(n,f) cross section was previously attempted at the CERN n_TOF facility EAR1 measuring station using the time-of-flight technique. Due to the low amount of available material and the given flux at EAR1, the measurement had to last several months to achieve a sufficient statistical accuracy. This long duration led to detector deterioration due to the prolonged exposure to the high α activity of the fission foils, therefore the measurement could not be successfully completed. Purpose: It is aimed to determine whether it is feasible to study neutron-induced fission at n_TOF/EAR2 and provide data on the Pu240(n,f) reaction in energy regions requested for applications. Methods: The study of the Pu240(n,f) reaction was made at a new experimental area (EAR2) with a shorter flight path which delivered on average 30 times higher flux at fast neutron energies. This enabled the measurement to be performed much faster, thus limiting the exposure of the detectors to the intrinsic activity of the fission foils. The experimental setup was based on microbulk Micromegas detectors and the time-of-flight data were analyzed with an optimized pulse-shape analysis algorithm. Special attention was dedicated to the estimation of the non-negligible counting loss corrections with the development of a new methodology, and other corrections were estimated via Monte Carlo simulations of the experimental setup. Results: This new measurement of the Pu240(n,f) cross section yielded data from 9meV up to 6MeV incident neutron energy and fission resonance kernels were extracted up to 10keV. Conclusions: Neutron-induced fission of high activity samples can be successfully studied at the n_TOF/EAR2 facility at CERN covering a wide range of neutron energies, from thermal to a few MeV