The prospects for enhanced Positron Emission Tomography imaging using liquid xenon (LXe) gamma ray detectors had been examined. Monte-Carlo simulations using GEANT4 were performed and the results were used to study the expected performance of a small animal PET scanner in comparison with a simulated conventional small animal scanner (LSO Focus 120). A NEMA-like cylinder phantom and an image contrast phantom were simulated with both scanners to compare performance characteristics. A Compton reconstruction algorithm was developed for the LXe scanner, and its performance and limitations studied.

No description available.

No description available.

The LSO scintillator crystal commonly used in PET scanners contains a low level of intrinsic radioactivity due to a small amount of Lu-176. This is not usually a concern in routine scanning but can become an issue in small animal imaging, especially when imaging low tracer activity levels. Previously there had been no systematic validation of simulations of this activity; this thesis discusses the validation of a GATE model of intrinsic Lu-176 against results from a bench-top pair of detectors and a Siemens Inveon preclinical PET system. The simulation results matched those from the bench-top system very well, but did not agree as well with results from the complete Inveon system due to a drop-off in system sensitivity at low energies that was not modelled. With this validation the model can now be used with confidence to predict the effects of Lu-176 activity in future PET systems.

Pour établir le comportement pharmacocinétique de nouveaux radiotraceurs en imagerie moléculaire, il est nécessaire d’approfondir l’analyse réalisée à partir d ’une image par l’ajout d’une mesure dynamique de la radioactivité dans le sang. L’Université de Sherbrooke développe présentement une plateforme microfluidique d’échantillonnage et d’analyse permettant la mesure de la radioactivité du plasma en temps réel. L’objectif du présent projet de maîtrise était de réaliser le composant optoélectronique responsable de la détection des positrons et de l’intégrer à la puce microfluidique. L’option retenue a été l’utilisation de photodiodes PIN en silicium. Un procédé de fabrication, ainsi qu’une série de photomasques ont été développés afin de produire une première itération de prototypes. Les détecteurs ont été conçus de manière à optimiser leur sensibilité en fonction du type de rayonnement à détecter. En effet, la région de détection doit être suffisamment épaisse et sensible pour absorber le maximum de particules énergétiques. Également, il est essentiel de minimiser le courant de fuite en noirceur afin d’obtenir un photocourant directement proportionnel à l’énergie des radiations incidentes. Les caractéristiques électriques obtenues avec les premiers détecteurs ont été démontrées proches des performances de détecteurs commerciaux similaires. De plus, il a été possible d’intégrer un canal microfluidique au substrat contenant les photodiodes et d’en réaliser l’encapsulation sans altérer les performances électriques initiales des détecteurs. Une courbe de l’activité radioactive du l8F a été mesurée, celle-ci se comparant à l’activité théorique associée à ce radioisotope communément utilisé en TEP. Enfin, un spectre en énergie des émissions radiatives du 18F a été mesuré et comparé aux performances de systèmes utilisant des photodiodes commerciales. D a été démontré que le prototype offrait un rapport signal sur bruit similaire aux systèmes basés sur des photodiodes commerciales. Des problèmes durant la fabrication ont cependant compromis les performances de la deuxième itération de détecteurs. Une série de recommandations finales afin d’éviter ces problèmes a été émise suite à la deuxième itération réalisée lors de ce projet de maîtrise.

Characterized by excessive myocardial glycogen deposition, cardiac hypertrophy, frequent cardiac arrhythmias and progressive conduction system disease, the PRKAG2 cardiac syndrome stems from a genetic mutation in the γ2-subunit of AMP-activated protein kinase (AMPK). Although functionally diverse, the main role of AMPK is to modulate cardiac metabolism in response to depleted ATP levels. A comprehensive study of the dysfunctional regulation of AMPK activity involved in the progression of the human PRKAG2 cardiac syndrome is hindered by the limitations of in vitro techniques. Positron emission tomography (PET) imaging with the glucose analogue, FDG, offers a quantitative assessment of myocardial glucose uptake non-invasively. The aim of this thesis was to determine the ability of FDG to detect changes in glucose uptake, storage and metabolism in the heart in relation to AMPK activity and provide insights into the mechanism of PRKAG2 cardiac hypertrophy. To achieve this aim, a transgenic AMPK γ2-subunit Arg302Gln mouse model was evaluated with small animal FDG PET with correlation to biochemical assays of cardiac AMPK activity and the glycogen metabolism pathway. Using the vena cava blood input function, FDG myocardial glucose uptake was reliably assessed in mice for the first time with Patlak modeling. Reduced FDG uptake in the Arg302Gln PRKAG2 mouse model suggested a feedback pathway reducing exogenous glucose uptake due to excessive intracellular glycogen stores. Despite an increase in FDG uptake in the skeletal muscle of the PRKAG2 mutant mice following insulin stimulation, there was no change in cardiac uptake, signifying myocardial insulin resistance. Increased reliance on glucose oxidation by TMZ inhibition of fatty acid oxidation reduced glycogen stores, restored cardiac function and eliminated ventricular preexcitation. The observed reduction in mouse myocardial FDG uptake mirrors the reduction previously observed in the human PRKAG2 patients. The potential now exists to evaluate both progression and therapeutic interventions for the PRKAG2 cardiac syndrome with the transgenic mouse model with translation to the affected patients using FDG cardiac imaging.

The LSO scintillator crystal commonly used in PET scanners contains a low level of intrinsic radioactivity due to a small amount of Lu-176. This is not usually a concern in routine scanning but can become an issue in small animal imaging, especially when imaging low tracer activity levels. Previously there had been no systematic validation of simulations of this activity; this thesis discusses the validation of a GATE model of intrinsic Lu-176 against results from a bench-top pair of detectors and a Siemens Inveon preclinical PET system. The simulation results matched those from the bench-top system very well, but did not agree as well with results from the complete Inveon system due to a drop-off in system sensitivity at low energies that was not modelled. With this validation the model can now be used with confidence to predict the effects of Lu-176 activity in future PET systems.

The prospects for enhanced Positron Emission Tomography imaging using liquid xenon (LXe) gamma ray detectors had been examined. Monte-Carlo simulations using GEANT4 were performed and the results were used to study the expected performance of a small animal PET scanner in comparison with a simulated conventional small animal scanner (LSO Focus 120). A NEMA-like cylinder phantom and an image contrast phantom were simulated with both scanners to compare performance characteristics. A Compton reconstruction algorithm was developed for the LXe scanner, and its performance and limitations studied.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 5 uppsatser.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available in print.