The DICOM-conformant PACS of the MGH was subjected to a performance study. The goal was to develop the tools needed to extract meaningful, quantitative measures related to performance with a view towards establishing reliable indicators that can help identify design weaknesses and performance changes over time. Efforts focused on operational scenarios such as moving images from servers to workstations, automatic routing and prefetching tasks. The performance of each process underlying these scenarios was studied using residency timing combined with a web-based monitoring system to yield quantitative data from various low-level resources on each server. While the critical processes and hardware on the PACS were already monitored to identify faults, the tools developed in this study now provide the means to assess overall performance issues. The results have yielded insights that have helped to identify faulty and inefficient logic in certain program constructs, and suggestions for design improvement and software enhancement. / Le PACS du HGM a été soumis à des études de performance. Le but était de développer des outils qui permettent d’obtenir des mesures quantitatives reliées aux performances, afin d’établir des indicateurs fiables permettant d’identifier des points faibles du design et des variations des performances. Les efforts ont été concentrés sur des scénarios opérationnels tels que le transfer d’images des serveurs aux stations de travail, et les services automatisés de distribution d’images. La performance de chacun des procédés utilisés pour ces scénarios a été étudié en utilisant le temps de résidence combiné avec un outils de surveillance du système qui permet ainsi l’acquisition de données quantitatives pour plusieurs ressources de base de chacun des serveurs. Bien que les principaux programmes, ainsi que les équipements du PACS, soient déjà sous surveillance, les outils developpés dans cette étude permettent d’évaluer les problèmes de performance global. Les résultats ont aidé à identifier des erreurs et des inneficacités dans les algorithmes de certains programmes, et ont permis de suggérer des améliorations au design ainsi qu’aux programmes. fr

We studied 42 rectal cancer brachytherapy patients with shielding included in the treatment, but without shielding included in the treatment planning and dose distribution calculations. To study the dose distribution in shielded cases, we first extracted relevant information from the PLATO BPS system and reconstructed the PLATO treatment plans with negligible errors. Based on this, we then implemented and validated the dose-superposition algorithm and applied this algorithm to all patients, finding that although the dose to healthy tissue is reduced, 10 of the 42 patients ended up with more than a 5% 'cold spot,' which is not acceptable in clinical practice. To solve this problem, a highly automated simulated annealing (SA) optimization algorithm, with a well-developed new cost function, was designed and implemented. The algorithm alone can decrease 'V90 to healthy tissue' by 17% while keeping the dose to target at the same level. By adding a shielding rod, the algorithm can further decrease the 'V90 to healthy tissue' by an additional 13%. The average calculation time for a patient using the dose-superposition algorithm was less than 20 seconds, and the time needed to make an SA based treatment plan for a shielded case was less than 10 minutes. The SA algorithm is independent of the physicist's experience. Two simplified algorithms for dose distribution calculation were investigated, the TG43 analytical shielding algorithm and the PLATO shielding algorithm. Their calculated results show conformal isodose lines to that from the dose-kernel-superposition algorithm, but present less accuracy and precision and much longer calculation times. Hence they are useful in limited conditions. Finally, we did some preliminary investigation / Nous avons étudié 42 cas de brachythérapie de cancer rectale avec protection incluse dans le traitement mais sans protection incluse dans la planification du traitement et calcul des distributions de doses. Pour étudier la distribution des doses dans les cas protégés, nous avons prélevé des informations importantes du système PLATO BPS et rétabli les plans de traitement PLATO avec des erreurs négligeables. Sur ces bases nous avons ensuite implémenté et validé les algorithmes de superposition des doses et appliqué ces algorithmes sur tous les patients, découvrant que bien que la dose pour tissu sain a été réduite, 10 des 42 patients se sont retrouvés avec plus de 5% de 'tache froide', ce qui est inacceptable dans les pratiques cliniques. Pour résoudre ce problème, nous avons conçu et implémenté un recuit simulé (RS) hautement automatisé pour optimisation de l'algorithme avec une nouvelle fonction de coût bien développée. L'algorithme en soi peut amoindrir 'V90 à tissu sain' de 17% tout en gardant les doses à objectif au même niveau. En ajoutant une baguette de protection, l'algorithme peut encore réduire le 'V90 à tissu sain' de 13% supplémentaires. Le calcul moyen de la durée pour un patient utilisant l'algorithme de superposition de dose est de moins de 20 secondes et le temps nécessaire pour un plan de traitement à base de RS pour un cas protégé fut moins de 10 minutes. L'algorithme RS est indépendant de l'expérience du physicien. Deux algorithmes simplifiés pour le calcul des doses de distribution ont été étudiés, l'algorithme TG43 de protection analytique et l'algorithme de protection PLATO. Leurs résultats calculés montrent des lignes isodoses conformes à des algorithmes d

This thesis presents an investigation of depth doses of 9-18 MeV electron beams measured with custom-built ionization chambers, film, and TLD in homogeneous solid water and bone-like phantoms as well as in a solid-water/bone heterogeneous phantom. Our measurement results show that dosimetry based on film and TLD corresponds well with ionization chamber dosimetry in both homogeneous and heterogeneous phantoms if appropriate methods for converting film or TLD responses to doses in phantom are used. We observed no clinically significant dose enhancement in relatively thin bone heterogeneities, however, we found dose enhancement in solid homogeneous bone phantoms. Work by previous investigators might have overestimated the dose in bone heterogeneities. We also found that the coefficient equivalent thickness (CET) method is suitable for estimating of dose in heterogeneous phantoms incorporating large uniform heterogeneities. / The thesis also presents an investigation of magnitudes, energies, and dose profiles of photon contaminations for 9-18 MeV electron beams with various field sizes used clinically. Our measurements show that the magnitude of photon contamination increases both with electron beam energy and with field size. The photon contamination dose profile is forward peaked and its energy decreases with an increase in field size.

Coronary arteries obstructed by atherosclerosis can be cleared by a balloon angioplasty accompanied by a permanent scaffolding implant ("stent"). There is, however, a 25--45% occurrence rate of excessive thickening of the treated vessel wall a few weeks post-angioplasty, leading to a re-obstruction of the vessel ("restenosis"), and recurrent symptoms. Endovascular radiotherapy, a potential preventive treatment against restenosis, can be delivered by a stent impregnated with radionuclides. The present thesis examines the local dosimetry of radioactive stents. A computer algorithm, D OSECOP, was developed based on the dose point kernel theory, to calculate the dose distribution created by a 32P-implanted stent in the surrounding vessel wall. The dosimetric significance of four parameters is also assessed, namely: (1) mechanical distortions of the stent, (2) the exact location of radionuclides on the stent, (3) the self-attenuation of the stainless steel stent, and (4) the width of the stent's struts in the calculation models.

This thesis presents the design, implementation and testing of a perfusion-weighted magnetic resonance imaging sequence that is capable of acquiring several slices at a time. Various methods of image acquisition and perfusion contrast generation are considered and tested. / The results of multi-slice acquisitions are compared with those from single-slice sequences in a variety of experiments to elucidate the effects of various imaging parameters on the measured perfusion signal. A seven slice version was implemented, and was found to give good results in the tests performed. This sequence will be useful in perfusion-based functional magnetic resonance imaging studies where the region of interest can not be covered with a single image slice.

The Radiology Department of the Montreal General Hospital was testing a digital system for gastrointestinal examinations. The goal of the study was to evaluate its potential in clinical situations, with the purpose of complementing or replacing the old fluoroscopic system available at the moment. / The core of our study was to image 18 surgical specimens with gastrointestinal pathology utilizing 3 different techniques: high resolution shielded-cabinet, the Siemens digital system and the conventional analog hard copy system. / A skin dose exposure test was conducted by the department with the purpose of assessing the benefits of both the digital and the conventional systems. / We concluded in this study that the many advantages of the digital system--lower skin exposure, image reconstruction and manipulation, fast access to images, overcome its inferior resolution as compared with the analog hard-copy generation system.

This thesis retrospectively analyzes prostate's daily motion provided by three-dimensional US localization and investigates its dosimetric impacts based on XVMC calculation which takes into account patient geometry, heterogeneity and prostate motion correction. The retrospective analysis on 32 prostate patients shows that the mean  SD displacements of prostate in the AP, SI, and RL directions are -3.3  7.9 mm, -1.1  6.4 mm, -0.2 5.6 mm, respectively. The largest rotation occurs about lateral axis with mean  SD of -0.9  4.6, ranging between -6.7 and 8.0 from a preliminary study including three patients. To assess the dosimetric impacts of prostate motion, five motion scenarios including with and without prostate translation and correction, with translation and rotation but no correction or only having translation correction are simulated. Analysis based on dose-volume histograms and isodose curves shows that prostate motion (translation and rotation) will deteriorate the dose delivered to patient target and OARs. With translation correction method, the degraded patient dose could be recovered nearly completely. For the scenarios with both translation and rotation, translation correction method could dramatically improve the degraded patient dose, but could not completely eliminate the dosimetric impact of prostate motion. Besides, the dosimetric impact of metal prosthesis in three patients has been analysed as well. Up to 5% discrepancies in their D90%, D95%, V90%, and D95% for PTV have been observed. / Le mouvement de la prostate est un problème critique dans le traitement conforme du cancer de la prostate, le plus commun cancer parmi les hommes au Canada. La radiothérapie guidée par l'image (IGRT) utilisant les images ultrasons (US) quotidiennes est une technique largement utilisée pour régler ce problème. Une nouvelle technique de localisation ultrasons en trois dimensions, basée sur une méthode de vérification intra modalités, a été testée à l'Hôpital General de Montreal en 2005. L'objectif principal de cette thèse a été de mieux quantifier l'amplitude du mouvement de la prostate à travers une analyse rétrospective de 32 patients et d'évaluer son impacte dans la dosimétrie des traitements de la prostate avec et sans localisation US. L'analyse rétrospective a montré que la moyenne  écart-type des mouvements de la prostate dans les directions AP, SI et DG est de -3.3  7.9 mm, -1.1  6.4 mm et -0.2  5.6 mm, respectivement. La plus grande rotation survient autour de l'axe latérale, avec une moyenne  écart-type de -0.9  4.6, s'échelonnant entre -6.7 et 8.0. Pour estimer l'impacte dosimétrique du mouvement rigide de la prostate, la dose a été calculée en utilisant la méthode XVMC, qui prend en considération la géométrie du patient, les hétérogénéités et les corrections pour le mouvement. Une déviation moyenne de la D95% de jusqu'à -11.9% a été observe pour le PTV, -5.1% pour le CTV et -4.2% pour le GTV. Le V95% du PTV a été réduit par un facteur de -22.2% lorsque la translation quotidienne de la prostate était présente mais aucune correction n'a été appliquée. La dégradation de la dose à la cible a pu être corrige presque complètement en appliquant une correction du mouvement de translation, cependant lorsque la rotation a été prise en compte, le recouvrement de la dose a été moins adéquat. L'effet des prothèses m

Thèse (Ph.D.)--Université de Sherbrooke (Canada), 2008. / Titre de l'écran-titre (visionné le 1 février 2007). In ProQuest dissertations and theses. Publié aussi en version papier.

Thèse (Ph.D.)--Université de Sherbrooke (Canada), 2007. / Titre de l'écran-titre (visionné le 1 février 2007). In ProQuest dissertations and theses. Publié aussi en version papier.

Recently, systems that integrate positron emission tomography and magnetic resonance imaging (PET/MR) have become available for clinical use. This new technology, which combines the high spatial resolution and superior soft-tissue contrast of MR with the picomolar sensitivity, quantitative capabilities, and wide array of tracers of PET, has the potential to benefit patients and provide insights that were previously unattainable in standalone systems. Simultaneous measurement of PET and MR parameters provides complementary information, allowing for a more complete assessment of disease, as well as cross validation and calibration of MR and PET measurements and techniques. To take full advantage of such a multi-modal system, accurate quantification of the PET data is necessary. Due to the low spatial resolution of PET – which can be further reduced by external factors like patient motion – and the inherent lack of anatomic detail, accurate quantification can be challenging. The simultaneously acquired MR information provides an opportunity to optimize PET quantification and analysis. In order to fully realize the benefits provided by the simultaneously acquired MR data, the MR data cannot be treated as discrete sequences, but as the continuous flow of information. This is due to differences in the time required for data collection to generate PET and MR images. This work describes the development and optimization of a pipeline for the reconstruction and analysis of PET data in a brain-dedicated prototype PET/MR system, the BrainPET (Siemens Healthcare). First, the performance of the BrainPET system was optimized for neurological imaging. MR-hardware interference and characteristics of the PET camera were quantified and a method for multimodal alignment was developed. To simplify and streamline the reconstruction and quantification process, a platform was designed which utilizes the functionality of a number of specialized brain imaging analysis software packages in an automated fashion. Second, MR-based methods addressing specific challenges to PET quantification were addressed. Simultaneously acquired structural MR data was used to correct the PET data for attenuation and partial volume effects. The use of MR data for motion correction was addressed and a unified algorithm which derives motion estimates from the PET data when MR data is unavailable was presented. Finally, the value of the optimized PET processing for neurological studies was evaluated in three instances: first an upper limit on the physiologic noise introduced by MR imaging on cerebral metabolism was estimated using PET and found to be minimal; next the benefit of MR-based motion correction and partial volume effect correction were estimated in a patient study; and lastly, a method to derive the PET radiotracer input function from the PET data using multiple MR sequences was presented. / Biophysics