Made available in DSpace on 2014-10-09T12:37:18Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:06Z (GMT). No. of bitstreams: 1 02029.pdf: 4740189 bytes, checksum: ff05d787c5ab98b675cc36bbe2b0c062 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Cette thèse traite de l'estimation de la concentration dans le sang artériel de molécules marquées par un radioélément émettant des positons. Cette concentration est appelée « fonction d'entrée artérielle B+ ». Elle doit être déterminée dans de nombreuses analyses en pharmacocinétique. Actuellement, elle est mesurée à l'aide d'une série de prélèvements artériels, méthode précise mais nécessitant un protocole contraignant. Des complications liées au caractère invasif de la méthode peuvent survenir (hématomes, infections nosocomiales).L'objectif de cette thèse est de s'affranchir de ses prélèvements artériels par l'estimation non-invasive de la fonction d'entrée B+ à l'aide d'un détecteur externe et d'un collimateur. Cela permet la reconstruction des vaisseaux sanguins afin de discriminer le signal artériel du signal contenu dans les autres tissus avoisinants. Les collimateurs utilisés en imagerie médicale ne sont pas adaptés à l'estimation de la fonction d'entrée artérielle B+ car leur sensibilité est très faible. Pour cette thèse, ils sont remplacés par des collimateurs codés, issus de la recherche en astronomie. De nouvelles méthodes pour utiliser des collimateurs à ouverture codée avec des algorithmes statistiques de reconstruction sont présentées.Des techniques de lancer de rayons et une méthode d'accélération de la convergence des reconstructions sont proposées. Une méthode de décomposition spatio-temporelle est également mise au point pour estimer efficacement la fonction d'entrée artérielle à partir d'une série d'acquisitions temporelles.Cette thèse montre qu'il est possible d'améliorer le compromis entre sensibilité et résolution spatiale en tomographie d'émission à l'aide de masques codés et d'algorithmes statistiques de reconstruction ; elle fournit également les outils nécessaires à la réalisation de tellesreconstructions. / This work deals with the estimation of the concentration of molecules in arterial blood which are labelled with positron-emitting radioelements. This concentration is called “ B+ arterial input function”. This concentration has to be estimated for a large number of pharmacokinetic analyses. Nowadays it is measured through series of arterial sampling, which is an accurate method but requiring a stringent protocol. Complications might occur during arterial blood sampling because this method is invasive (hematomes, nosocomial infections).The objective of this work is to overcome this risk through a non-invasive estimation of B+ input function with an external detector and a collimator. This allows the reconstruction of blood vessels and thus the discrimination of arterial signal from signals in other tissues.Collimators in medical imaging are not adapted to estimate B+ input function because their sensitivity is very low. During this work, they are replaced by coded-aperture collimators, originally developed for astronomy.New methods where coded apertures are used with statistical reconstruction algorithms are presented. Techniques for analytical ray-tracing and for the acceleration of reconstructions are proposed. A new method which decomposes reconstructions on temporal sets and on spatial sets is also developped to efficiently estimate arterial input function from series of temporal acquisitions.This work demonstrates that the trade-off between sensitivity and spatial resolution in PET can be improved thanks to coded aperture collimators and statistical reconstruction algorithm; it also provides new tools to implement such improvements.

SPECT (Single Photon Emission Computed Tomography) is the modality of choice for myocardial perfusion imaging due to the high sensitivity and specificity, and the lower cost of equipment and radiotracers compared to PET. Dynamic SPECT imaging provides new possibilities for myocardial perfusion imaging by encoding more information in the reconstructed images in the form of time-activity functions. The recent introduction of small solid-state SPECT cameras using multiple pinhole collimators, such as the GE Discovery NM 530c, offers the ability to obtain accurate myocardial perfusion information with markedly decreased acquisition times and offers the possibility to obtain quantitative dynamic perfusion information. This research targets two aspects of dynamic SPECT imaging with the intent of contributing to the improvement of projection and reconstruction methods. First, we propose an adaptation of distance-driven projection to SPECT imaging systems using single-pinhole collimator detectors. The proposed distance-driven projection approach accounts for the finite size of the pinhole, the possibly coarse discretization of the detector and object spaces, and the tilt of the detector surface. We evaluate the projection method in terms of resolution and signal to noise ratio (SNR). We also propose two maximum a posteriori (MAP) iterative image reconstruction methods employing kernel density estimators. The proposed reconstruction methods cluster time-activity functions (or intensity values) by their spatial proximity and similarity, each of which is determined by spatial and range scaling parameters respectively. The results of our experiments support our belief that the proposed reconstruction methods are especially effective when performing reconstructions from low-count measurements. / Thesis / Doctor of Philosophy (PhD)

Made available in DSpace on 2014-10-09T12:28:43Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:15Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:28:43Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:15Z (GMT). No. of bitstreams: 0 / Este trabalho apresenta as medidas das taxas de reação nuclear ao longo da direção radial da pastilha combustível por irradiação e posterior espectrometria gama de um fino disco de UO2 com enriquecimento de 4,3% no reator IPEN/MB- 01. A partir de sua irradiação, a taxa de captura radioativa e de fissão foram medidas em função do raio do disco utilizando um detector HPGe. Colimadores de chumbo foram utilizados para esse fim. O disco de UO2 é inserido no interior de uma vareta combustível desmontável e esta é então colocada na posição central do núcleo do reator IPEN/MB-01 e irradiada durante uma hora sob um fluxo de nêutrons de aproximadamente 9 x 108 n/cm2s. Na espectrometria gama, 10 colimadores com diâmetros diferentes foram utilizados, consequentemente, as reações nucleares de captura radioativa que ocorrem nos átomos de 238U e as fissões que ocorrem em ambos 235U e 238U são mensuradas em função de 10 regiões distintas do disco combustível. Correções de eficiência geométrica devido à introdução dos colimadores no sistema de detecção HPGe foram estimados usando o código MCNP-4C. Alguns valores calculados da taxa de reação nuclear de captura radioativa e fissão obtidos pela metodologia de Monte Carlo, utilizando o código MCNP-4C, são apresentados e comparados aos dados experimentais apresentando boa concordância. Além de taxas de reação nuclear, os índices espectrais 28ρ e 25δ foram obtidos para cada raio do disco combustível. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP