OPTIMISATION DE LA RECONSTRUCTION COMPLÈTE 3D EN TOMOGRAPHIE PAR ÉMISSION DE POSITONS DU PETIT ANIMAL PAR MODÉLISATION MONTE-CARLO DE LA MATRICE SYSTÈME

The quality of PET images depends strongly on the image reconstruction method. Statistical iterative methods help to reduce the impact of the physical artefact sources on the image, since they can incorporate a model of the system response. We implemented fully 3-D reconstruction technique based on an accurate description of the system response to reconstruct listmode data. The main feature of our method, named SIMALIR, is the off-line calculation of the system probability matrix by Monte Carlo simulations. It was applied on the Philips MOSAICTM animal PET system. The tomograph was simulated using GATE toolkit. A comprehensive evaluation of the MOSAICTM model was performed in order to describe reliably the system response function. The SIMALIR method was compared with FBP, RAMLA-3D and MLEM using phantoms and mice data. The results show that SIMALIR improves considerably the images quality compared to classical PET reconstruction algorithms.La qualité des images en TEP est directement liée à l'algorithme de reconstruction utilisé. Les méthodes de reconstruction statistiques peuvent modéliser, via la matrice système, les différents phénomènes physiques qui détériorent la qualité des images. Notre approche consiste d'une part, à modéliser les différents phénomènes géométriques et physiques, au moyen de l'outil de simulation Monte-Carlo, et d'autre part, à exploiter les données dans un format "mode-liste" présentant de nombreux avantages, afin de les reconstruire à l'aide d'un algorithme de reconstruction 3D. Cette méthode, appelée SIMALIR, a été appliquée et étudiée sur la caméra MOSAIC(TM) de Philips, système TEP dédié au petit animal qui a fait l'objet d'une modélisation à l'aide de la plateforme GATE. Les principales performances du modèle simulé et particulièrement la distribution spatiale ont été testées et validées, afin de pouvoir les exploiter dans la modélisation de la matrice système. Les résultats précliniques et sur des objets tests ont montré que la méthode SIMALIR permet d'améliorer considérablement la qualité des images reconstruites par rapport aux programmes de reconstruction classiques

Optimisation de la reconstruction complète 3D en tomographie par émission de positons du petit animal par modélisation monte-carlo de la matrice système

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Pregnancy promotes melanoma metastasis through enhanced lymphangiogenesis

The relationships of pregnancy and melanoma have been debatable. Our aim was to assess the influence of gestation on the course of melanoma in a classic murine model of tumor progression and in women. B16 mouse melanoma cells were injected in nonpregnant or pregnant mice on day 5 of gestation. Animals were evaluated for tumor progression, metastases, and survival. Tumor sections were analyzed for lymphatic and blood vessel number and relative surface and expression of angiogenic growth factors. Finally, primary melanomas from pregnant and nonpregnant women, matched for age and tumor thickness, were also considered. Tumor growth, metastasis, and mortality were increased in B16-injected pregnant mice. Tumors displayed an increase in intratumoral lymphangiogenesis during gestation. This increased lymphatic angiogenesis was not observed in normal skin during gestation, showing its specificity to the tumor. An analysis of melanoma from pregnant and matched nonpregnant women showed a similar increase in lymphatic vessels. Tumors from pregnant mice had increased expression of vascular endothelial growth factor A at the RNA and protein levels. The increased vascular endothelial growth factor A production by melanoma cells could be reproduced in culture using pregnant mouse serum. In conclusion, pregnancy results in increased lymphangiogenesis and subsequent metastasis. Caution should be applied in the management of patients with advanced-stage melanoma during gestation