Targeted fully 3D Monte Carlo reconstruction in SPECT

PCSV, présenté par Z. El Bitar, soumis aux proceedingsFully 3D Monte-Carlo (F3DMC) reconstruction consists in calculating a fully 3D object-specific system matrix using Monte-Carlo simulations and inverting it using an iterative approach. To reduce the large amount of disk space required by this approach, we derived a targeted F3DMC approach (TF3DMC) in which the volume to be reconstructed is irregularly sampled, so that pre-identified functional regions of interest are reconstructed using fine sampling while regions with non-specific activity or without any particular interest are coarsely sampled. This method was assessed using simulated and real SPECT data of a phantom filled with Tc99m. The GATE Monte-Carlo simulator was considered to simulate the phantom data and to calculate the system matrices needed for the reconstruction of the simulated and of the real SPECT data. Activity ratios measured in TF3DMC images were compared with those measured on F3DMC and OSEM images corrected for scatter, attenuation and detector response function. TF3DLMC yielded errors less than 10% in activity ratio estimates in hot regions, while errors with quantitative OSEM were between -21% and -3%. The space needed to store the system matrix was divided by a factor from 3.5 to 9.4 compared to F3DMC, for similar or even better accuracy in activity ratio estimates. These results suggest that TF3DMC can be made practical and outperforms F3DMC and OSEM in terms of quantitative accuracy

Helium mixtures in nanotube bundles

An analogue to Raoult's law is determined for the case of a 3He-4He mixture adsorbed in the interstitial channels of a bundle of carbon nanotubes. Unlike the case of He mixtures in other environments, the ratio of the partial pressures of the coexisting vapor is found to be a simple function of the ratio of concentrations within the nanotube bundle.Comment: 3 pages, no figures, submitted to Phys. Rev. Let

Monte Carlo Simulation With The GATE Software Using Grid Computing

DémonstrationInternational audienceMonte Carlo simulations needing many replicates to obtain good statistical results can be easily executed in parallel using the "Multiple Replications In Parallel" approach. However, several precautions have to be taken in the generation of the parallel streams of pseudo-random numbers. In this paper, we present the distribution of Monte Carlo simulations performed with the GATE software using local clusters and grid computing. We obtained very convincing results with this large medical application, thanks to the EGEE Grid (Enabling Grid for E-sciencE), achieving in one week computations that could have taken more than 3 years of processing on a single computer. This work has been achieved thanks to a generic object-oriented toolbox called DistMe which we designed to automate this kind of parallelization for Monte Carlo simulations. This toolbox, written in Java is freely available on SourceForge and helped to ensure a rigorous distribution of pseudo-random number streams. It is based on the use of a documented XML format for random numbers generators statuses

GINSENG (Global Initiative for Sentinel E-health Network on Grid)

The GINSENG (Global Initiative for Sentinel E-health Network on Grid) project aims to implement a grid infrastructure for ehealthand epidemiology in Auvergne. A distributed medical database is created upon a secure network for epidemiologicalstudies. Our goal is to create a decentralized information system using grid technologies. The medical sites involved in theproject are clustered around two themes: cancer monitoring and perinatal care. On each medical site a server whichduplicates the medical database, is deployed with grid services. At the same time, full control of the information is kept by theorganizations storing patients' files. This solution allows for a high level of security, privacy, availability, and fault tolerance.Queries made on the distributed medical databases are made via a secure web portal. Public health authorities use thisinfrastructure for health monitoring, epidemiological studies and evaluation of specific medical practices

A Statistical Mechanical Problem in Schwarzschild Spacetime

We use Fermi coordinates to calculate the canonical partition function for an ideal gas in a circular geodesic orbit in Schwarzschild spacetime. To test the validity of the results we prove theorems for limiting cases. We recover the Newtonian gas law subject only to tidal forces in the Newtonian limit. Additionally we recover the special relativistic gas law as the radius of the orbit increases to infinity. We also discuss how the method can be extended to the non ideal gas case.Comment: Corrected an equation misprint, added four references, and brief comments on the system's center of mass and the thermodynamic limi

Natural and anthropogenic lead in sediments of the Rotorua lakes, New Zealand

Global atmospheric sources of lead have increased more than 100-fold over the past century as a result of deforestation, coal combustion, ore smelting and leaded petroleum. Lead compounds generally accumulate in depositional areas across the globe where, due to low solubility and relative freedom from microbial degradation, the history of their inputs is preserved. In lakes there is rapid deposition and often little bioturbation of lead, resulting in an excellent depositional history of changes in both natural and anthropogenic sources. The objective of this study was to use sediments from a regionally bounded set of lakes to provide an indication of the rates of environmental inputs of lead whilst taking into account differences of trophic state and lead exposure between lakes. Intact sediment gravity cores were collected from 13 Rotorua lakes in North Island of New Zealand between March 2006 and January 2007. Cores penetrated sediments to a depth of 16–30 cm and contained volcanic tephra from the 1886 AD Tarawera eruption. The upper depth of the Tarawera tephra enabled prescription of a date for the associated depth in the core (120 years). Each core showed a sub-surface peak in lead concentration above the Tarawera tephra which was contemporaneous with the peak use of lead alkyl as a petroleum additive in New Zealand. An 8 m piston core was taken in the largest of the lakes, Lake Rotorua, in March 2007. The lake is antipodal to the pre-industrial sources of atmospheric lead but still shows increasing lead concentrations from <2 up to 3.5 μg g−1 between the Whakatane eruption (5530 ± 60 cal. yr BP) and the Tarawera eruption. Peaks in lead concentration in Lake Rotorua are associated with volcanic tephras, but are small compared with those arising from recent anthropogenic-derived lead deposition. Our results show that diagenetic processes associated with iron, manganese and sulfate oxidation-reduction, and sulfide precipitation, act to smooth distributions of lead from anthropogenic sources in the lake sediments. The extent of this smoothing can be related to changes in sulfate availability and reduction in sulfide driven by differences in trophic status amongst the lakes. Greatest lead mobilisation occurs in mesotrophic lakes during seasonal anoxia as iron and manganese are released to the porewater, allowing upward migration of lead towards the sediment–water interface. This lead mobilisation can only occur if sulfides are not present. The sub-surface peak in lead concentrations in lake sediments ascribed to lead alkyl in petroleum persists despite the diagenetic processes acting to disperse lead within the sediments and into the overlying water

К всеобщим свойствам экономического пространства: науковедческий анализ

Определяются всеобщие свойства экономического пространства. Сделана попытка осмыслить современные тенденции в развитии экономической науки. Рассматриваются общие проблемы состояния и развития мировой экономики, ее глобализации.Визначено загальні властивості економічного простору. Зроблено спробу осмислити сучасні тенденції у поступі економічної науки. Розглядаються загальні проблеми стану та розвитку світової економіки, її глобалізації.The paper outlines general features of an economic area. A try is made to rethink latest tendencies in the stride of economic science. Also, broad problems related with the performance and globalization of worldwide economics are discussed

Using Genetic Variation to Explore the Causal Effect of Maternal Pregnancy Adiposity on Future Offspring Adiposity: A Mendelian Randomisation Study

Background: It has been suggested that greater maternal adiposity during pregnancy affects lifelong risk of offspring fatness via intrauterine mechanisms. Our aim was to use Mendelian randomisation (MR) to investigate the causal effect of intrauterine exposure to greater maternal body mass index (BMI) on offspring BMI and fat mass from childhood to early adulthood. Methods and Findings: We used maternal genetic variants as instrumental variables (IVs) to test the causal effect of maternal BMI in pregnancy on offspring fatness (BMI and dual-energy X-ray absorptiometry [DXA] determined fat mass index [FMI]) in a MR approach. This was investigated, with repeat measurements, from ages 7 to 18 in the Avon Longitudinal Study of Parents and Children (ALSPAC; n = 2,521 to 3,720 for different ages). We then sought to replicate findings with results for BMI at age 6 in Generation R (n = 2,337 for replication sample; n = 6,057 for total pooled sample). In confounder-adjusted multivariable regression in ALSPAC, a 1 standard deviation (SD, equivalent of 3.7 kg/m2) increase in maternal BMI was associated with a 0.25 SD (95% CI 0.21–0.29) increase in offspring BMI at age 7, with similar results at later ages and when FMI was used as the outcome. A weighted genetic risk score was generated from 32 genetic variants robus

Bose-Einstein Condensate in Weak 3d Isotropic Speckle Disorder

The effect of a weak three-dimensional (3d) isotropic laser speckle disorder on various thermodynamic properties of a dilute Bose gas is considered at zero temperature. First, we summarize the derivation of the autocorrelation function of laser speckles in 1d and 2d following the seminal work of Goodman. The goal of this discussion is to show that a Gaussian approximation of this function, proposed in some recent papers, is inconsistent with the general background of laser speckle theory. Then we propose a possible experimental realization for an isotropic 3d laser speckle potential and derive its corresponding autocorrelation function. Using a Fourier transform of that function, we calculate both condensate depletion and sound velocity of a Bose-Einstein condensate as disorder ensemble averages of such a weak laser speckle potential within a perturbative solution of the Gross-Pitaevskii equation. By doing so, we reproduce the expression of the normalfluid density obtained earlier within the treatment of Landau. This physically transparent derivation shows that condensate particles, which are scattered by disorder, form a gas of quasiparticles which is responsible for the normalfluid component