IMAGERIE DIAGNOSTIQUE DES TUMEURS DU TRONC CEREBRAL CHEZ L'ENFANT (A PROPOS DE 9 CAS VUS EN SERVICE DE PEDIATRIE GENERALE)

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Anatomie in vivo de l'encéphale et de la voûte en IRM (quantification informatisée et normalisation)

Le but de ce travail est de quantifier en IRM les structures cérébrales du sujet sain et d'en normaliser les résultats. Matériels et méthodes : Le travail comporte l'étude des points de crâniométrie et des sutures (n=150), l'analyse de la voûte et du parenchyme (20-80 ans, n=126), la segmentation automatique de la voûte et du parenchyme à partir de données en 3D (témoins 20-49 ans, n=30 ans). Résultats : La voûte et les sutures sont analysables en IRM. La taille de la voûte est corrélée à la taille du sujet. Avec l'âge, le V3 s'élargit (r=0,78), les dimensions de la voûte sont stables. Dans le plan bi-commissural, l'indice surfacique CA-CP (rapport surface du parenchyme sur surface du contenu de la voûte, délimitée par la table externe) est de 0,73 +- 0,02 de 20-49 ans. Conclusion : Les paramètres de la crâniométrie sont analysables en IRM. L'indice surfacique CA-CP, permet une quantification normalisée précise complètement automatisée et reproductible des structures cérébralesLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Apport de l'IRM à l'étude du pronostic des accidents ischémiques aigus carotidiens traités par thrombolyse intraveineuse

Nous avons étudié l'apport de l'IRM au pronostic des accidents ischémiques aigus carotidiens traités par thrombolyse intraveineuse. Une IRM multimodale a été réalisée chez 49 patients consécutifs, avant thrombolyse, et répétée à J1. L'évolution clinique a été appréciée à J60 par le score NIHSS et le score de Rankin modifié. L'évolution tissulaire a été quantifiée sur une séquence pondérée T2 à J60. Une évolution clinique et une évolution tissulaire favorables étaient associées à un score NIHSS initial faible, à des volumes initiaux peu étendus d'anomalies de diffusion et de perfusion, à un site d'occlusion artérielle relativement distal, et à la recanalisation artérielle à J1. Le site de l'occlusion et le TTP mesuré dans l'anomalie de diffusion étaient prédictifs à J0 de la recanalisation artérielle. La visibilité anormale des veines transcérébrales en T2* était prédictive du risque de transformation hémorragiqueLYON1-BU.Sciences (692662101) / SudocSudocFranceF

The solubilisation of Ru and U from condensation particles released by overheated nuclear fuel and maturated in air and in argon

The emission of uranium and ruthenium oxides from overheated nuclear fuel is a complex phenomenon which depends on fuel matrix, temperature, oxygen potential of the atmosphere in contact and on emission sequence. Furthermore, secondary annealing ("maturation") reactions of aerosol particles in the gas phase, immediately after emission, strongly influence the properties of particles before their dispersion in the reactor containment building and/or in the environment. Maturation influences surface and bulk gradient composition, particle size, and, as a consequence, weathering rates in the environment. This paper describes how emission and maturation conditions may affect the solubility rates of condensation particles released by overheated U and Ru oxides mixtures, in small-scale laboratory simulations. It will be demonstrated that the presence of Ru decreases the solubilisation rate of U

Contamination of quartz surfaces by Cs, Sr and U from deposited UO2 aerosol particles

This paper describes the mechanisms likely to lead to a practically irreversible contamination of quartz (in concrete, for example) after deposition of radioactive aerosol particles released by overheated nuclear fuel. Contamination results from diffusion of Cs, Sr and UO2 into quartz from deposited condensation particles. In laboratory experiments, submicronic condensation particles were deposited onto quartz surfaces and annealed for 3 hours at 700, 900 and 1100 degreesC in different atmospheres. The contamination potential of deposited radioactive material depends on the characteristics of the UO2 particle matrices, on temperature and on the oxidizing potential of the atmosphere in contact

Time-dependent emission of U from overheated UO2 pellets

The emission of uranium oxides from overheated nuclear fuels proceeds as a function of time. depending mainly on temperature. oxygen potential of the amosphere in contact. and structure and composition of the fuel matrix itself. This Lime dependent emission results in variation of the U-concentration in the released aerosol. The subsequent annealing ("maturation") reactions acting on the aerosol particles are greatly affected bq the emission sequence of the different elements. The maturation phase strongly influences the properties of particles dispersed in thr environment: e.g. the rate of leaching of the particles is particularly sensitive to their "chemical history"

A time-dependent emission of some radionuclides from overheated nuclear fuel

The physico-chemical characteristics of particles emitted by an overheated nuclear fuel may be significantly modified when they are put in contact with an oxidizing atmosphere at temperatures of the order of 700-900 degrees C. This so-called "maturation" stage induces reactions between radioelements and the UOx matrix of the aerosol particles. These reactions, in turn, deeply influence the solubility of radioelements in the environment. This paper presents experiments aimed at describing the behavior of characteristic radioactive elements present in nuclear fuel (Cs, Sr, Tb), which are emitted as a consequence of an accidental thermal excursion. As the sequence of radionuclide emission from the nuclear fuel depends on the volatility of their chemical forms, it has to be expected that the maturation stage itself is a time-dependent process in the sequence of emission events

The influence of maturation stage on the solubility of fission products from aerosols emitted by overheated nuclear fuels

In case of a nuclear reactor accident, radionuclides are emitted in chemical forms which determine their mobility in the environment. Two stages are important in this aspect: (i) the emission stage which depends on the temperature and composition of the nuclear fuel and (ii) the so called 'maturation stage' during which UO2 aerosols react with gases and vapours in the plume of the damaged reactor or in the atmosphere of the confinement structure. The oxidizing nature and the temperature of the reacting gases exert a strong influence on the solubility of fission products carried by UO2 aerosols

Study of Ru released under accidental conditions by overheated nuclear fuel: the emission of Ru and U

The emission of uranium and ruthenium oxides from overheated nuclear fuel is a complex phenomenon which depends on the fuel matrix, on temperature, on the oxygen potential of the amosphere in contact and on the emission sequence. All these factors influence the properties of particles before their dispersion in the reactor containment building and in the environment: these properties are, among others, surface composition, particle size, and, as a consequence, weathering rates in the environment. Emission in air increases the solubility of U-oxides mainly. This first paper describes the main physico-chemical characteristics of condensation particles released by overheated U and Ru oxides mixtures, in small-scale laboratory simulations