The optimisation of image quality in medical imaging techniques is a significant factor in favourable patient prognoses. The number of counts in a nuclear medicine image is one factor in determining the diagnostic value of the image. The current study aims to determine the variation in counts in whole-body bone scan images with patient height and weight. Three separate studies were undertaken as part of the investigation. First, 65 whole-body bone scans were analysed together with patient height, weight, age and sex. Weight was found to the most important anatomy influence on image counts. However, significant influences from patient sex and age meant that a useful relationship between image counts and patient anatomy based solely on height and weight could not be determined. For the second study, a model of General Electric Millennium MG gamma camera was created and validated within the SIMIND Monte Carlo software. The results indicate that the model is an accurate representation of the gamma camera. Third, the 4D NCAT whole-body patient phantom was modified to represent the average male and female clinical study participants. The phantoms were used in conjunction with the gamma camera model to simulate the whole-body bone scan procedure. The counts in the simulated images were consistent with the average measured counts of the clinical study indicating that it is feasible to use the NCAT phantom for nuclear medicine bone imaging. However, the phantom’s method of activity distribution should be refined to allow a more realistic distribution of activity throughout the skeleton.

The optimisation of image quality in medical imaging techniques is a significant factor in favourable patient prognoses. The number of counts in a nuclear medicine image is one factor in determining the diagnostic value of the image. The current study aims to determine the variation in counts in whole-body bone scan images with patient height and weight. Three separate studies were undertaken as part of the investigation. First, 65 whole-body bone scans were analysed together with patient height, weight, age and sex. Weight was found to the most important anatomy influence on image counts. However, significant influences from patient sex and age meant that a useful relationship between image counts and patient anatomy based solely on height and weight could not be determined. For the second study, a model of General Electric Millennium MG gamma camera was created and validated within the SIMIND Monte Carlo software. The results indicate that the model is an accurate representation of the gamma camera. Third, the 4D NCAT whole-body patient phantom was modified to represent the average male and female clinical study participants. The phantoms were used in conjunction with the gamma camera model to simulate the whole-body bone scan procedure. The counts in the simulated images were consistent with the average measured counts of the clinical study indicating that it is feasible to use the NCAT phantom for nuclear medicine bone imaging. However, the phantom’s method of activity distribution should be refined to allow a more realistic distribution of activity throughout the skeleton.

This survey has shown, using the Monte Carlo N-Particle(MCNP) code to model a detection system, to demonstrate that it is possible to design a system to measure hazard elements in polluted water. At first, the measurement method needs to be determined. For measuring the specimen component without knowing the accuracy concentration in a short time, when compared with other methods, the Energy-dispersive X-ray fluorescence (ED-XRF) is a good choice for solving this problem. Then, a basic part of this method and actual experiment setting is using the simulation to find the suitable parameters such as the input X-ray energy level, the detector thickness, etc. At last, the polluted water has been measured for evaluating the system function.

La Radiothérapie Interne Vectorisée (RIV) consiste à détruire des cibles tumorales en utilisant des vecteurs radiomarqués (radiopharmaceutiques) qui se lient sélectivement à des cellules tumorales. Dans un contexte d'optimisation de la RIV, une meilleure détermination du dépôt d'énergie dans les tissues biologiques est primordiale pour la définition d'une relation dose absorbée - effet biologique et pour l'optimisation des traitement du cancer. Cela nécessite une évaluation quantitative de la distribution de l'activité (avec la technique d'imagerie moléculaire la plus appropriée) et d'effectuer le transport du rayonnement à l'échelle à laquelle se produisent les phénomènes biologiques pertinents. Les méthodologies à appliquer et les problématiques à établir dépendent strictement de l'échelle (cellule, tissu, organe) de l'application considérée, et du type de rayonnement en cause (photons, électrons, particules alpha). Mon travail de recherche a consisté à développer des techniques dosimétriques dédiées (dosimétrie mono-échelle) et innovantes, capables de prendre en compte la particularité de différents scénarios expérimentaux (cellulaire, pré-clinique, RIV clinique). / Targeted Radionuclide Therapy (TRT) consists in killing tumour targets by using radiolabeled vectors (radiopharmaceuticals) that selectively bind to tumour cells. In a context of TRT optimization, a better determination of energy deposition within biologic material is a prerequisite to the definition of the absorbed dose-effect relationship and the improvement of future cancer treatment. This requires being able to quantitatively assess activity distribution (with the most appropriate molecular imaging technique) and perform radiation transport at the scale at which biologically relevant phenomena occur. The methodologies that should be applied and the problematic to be faced strictly depend on the scale (cell, tissue, body) of the application considered, and on the type of radiation involved (photons, electrons, alpha). This research work consisted in developing dedicated dosimetric techniques (single-scale dosimetry) capable of taking into account the peculiarity of different experimental scenarios (cellular, pre-clinical, clinical TRT).

Dans un site de stockage profond de déchets radioactifs, l’utilisation de matériaux à base de ciment Portland en association avec de l’argile pourrait se révéler inadaptée en raison de leur forte alcalinité. Une alternative serait de mettre en œuvre des ciments générant des solutions interstitielles de pH réduit (de l’ordre de 11 au lieu de 13,5 pour un CEM I). Les formulations étudiées dans cette thèse font appel à des ciments composés (également appelés « liant bas pH ») élaborés à partir de mélanges binaires (CEM I / fumée de silice) ou ternaires (CEM I / fumée de silice / cendres volantes ou laitier), avec de forts taux de substitution du CEM I (de 30% à 80%). Le travail réalisé répond à un double objectif : (i) étudier l’évolution chimique des liants bas pH à 50°C ou 80°C, températures qui pourraient être rencontrées dans certaines zones du stockage, et (ii) préciser les mécanismes à l’origine de la bonne rétention des alcalins par ces liants hydratés. (i) Le suivi sur une période d’un an de pâtes de liant bas pH montre que l’accroissement de la température de 20 à 80°C accélère l’hydratation des liants et favorise la consommation de la portlandite. L’allongement et la réticulation des chaînes de silicates des C-A-S-H est mise en évidence par RMN de l’27Al et du 29Si. L’ettringite observée dans les pâtes conservées à 20°C est par ailleurs déstabilisée. Les sulfates ainsi relâchés sont pour partie adsorbés sur les C-A-S-H et dissous dans la solution interstitielle. Le pH de cette dernière est réduit de 1,7 à 2,2 unités selon les formulations. En revanche, les fractions solubles d’alcalins n’évoluent pas de façon importante. Le liant ternaire T1 composé de 37,5% de CEM I, 32,5% de fumée de silice et 30% de cendres volantes est le seul des ciments étudiés à conduire à un pH de solution interstitielle inférieur à 11 aux trois températures considérées (20, 50 et 80°C - échéances 6 mois et 1 an). Son évolution à plus long terme a pu être simulée à l’aide de systèmes modèles reproduisant sa composition chimique à partir d’oxydes réactifs. A l’équilibre thermodynamique, l’assemblage minéralogique est constitué de C-A-S-H (rapports Ca/Si et Al/Si de 0,75 et 0,15 respectivement) ainsi que d’hydroxyde d’aluminium et de silice amorphes, et il impose un pH de 10,3 à 20°C. (ii) Ce sont les C-A-S-H qui jouent le rôle essentiel dans la rétention des alcalins. Le mécanisme mis en jeu est celui d’une compensation des charges négatives des C-A-S-H par interaction électrostatique. Il existe une sélectivité de sorption : le potassium est mieux retenu que le sodium. Celle-ci pourrait être attribuée en première approche à la différence de rayon solvaté entre ces ions. Une modélisation Monte Carlo des interactions électrostatiques entre des particules de C-S-H et un électrolyte contenant des ions sodium et potassium montre cependant que cette hypothèse ne suffit pas à elle seule à expliquer la sélectivité observée expérimentalement. / Because of their high alkalinity, Portland cement (OPC)-based materials may have deleterious effects in an underground waste repository. A solution would be to use low-alkalinity cements (also referred as low-pH cements) generating interstitial solutions with a reduced pH (11 instead of 13.5 for OPC), and thus showing an improved chemical compatibility with the repository environment. In this work, the investigated formulations were based on binary (OPC / silica fume) or ternary (OPC / silica fume / slag or fly ash) blends, with high substitution levels of CEM I (from 30% to 80%). This research project met two main objectives: (i) study the chemical evolution of low-pH cements at 50°C or 80°C, since such temperatures could be encoutered in certain zones of the waste repositories, and (ii) determine the mechanisms of alkali retention by hydrated low-pH cements. (i) Investigation of low-pH cement pastes with ongoing hydration over one year showed that increasing the temperature from 20°C to 80°C accelerated cement hydration and favoured the depletion of portlandite. A lengthening of the C-A-S-H silicate chains was also detected by 27Al and 29Si NMR analyses. Besides, ettringite precipitated at 20°C, but was destabilised at higher temperature. The released sulphates were partly adsorbed on the C-A-S-H and dissolved in the interstitial solution. The pH of this solution was reduced from 1.7 to 2.2 units depending on the formulations. The soluble fractions of alkalis did not significantly change with temperature. Among the five investigated blends, ternary binder T1 (37.5% CEM I, 32.5% silica fume, 30% fly ash) was the only one giving a pore solution pH lower than 11 at 20, 50 and 80°C (curing time of 6 months and 1 year). Its long-term evolution was simulated by model systems reproducing its chemical composition with reactive oxides. At equilibrium, the hydrate assemblage comprised C-A-S-H (Ca/Si and Al/Si ratios of 0.75 and 0.15 respectively), amorphous silica and aluminium hydroxide. It led to a pH of 10.3 at 20°C. (ii) C-A-S-H hydrates played a major role in the retention of alkalis. Sorption of potassium was higher than that of sodium and mainly resulted from electrostatic interactions with C-A-S-H. Monte Carlo modelling of these interactions showed that the difference of solvated radii between these ions could not explain by itself the sorption selectivity experimentally observed.