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Thèses en cours

Benjamin Auer

(50% ministère / 50% Région)
Quantitative reconstruction methods dedicated to small animal SPECT.

In Single Photon Emission Computed Tomography (SPECT), attenuation and scatter introduce important artifacts in the reconstructed images skewing the diagnosis and the follow-up of the subject. Indeed, the presence of scatter results in a blurring, and haziness of the observed projections reduces the reconstructed contrast and introduces a significant uncertainty in quantification of the underlying activity distribution. The use of accurate modeling can result in reduced artifacts, improved detection ability and contrast to noise ratio, images with larger quantitative differences between defect and non-defect cases, less sensitivity to anatomical variations and more accurate quantification.

My research project focuses on the development of several quantitative reconstruction methods dedicated to small animal SPECT. The latter is based on modeling the acquisition process of a pinhole SPECT system available at our institute using Monte Carlo simulations. The system matrix approach, combined with an iterative reconstruction algorithm, enabled to characterize the system performance and to compare it to the state of the art.

Gold standard Monte Carlo Simulation is one of the well-established tools that has been used in SPECT image reconstruction due to its ability to accurately model photon transport. However, MCS requires extensive computation time to obtain a low noise system matrix and are therefore inappropriate for the rate of daily exams performed in both clinical and preclinical routine : an improvement in simulation speed is thus mandatory.

The major drawbacks of Monte Carlo methods led us to develop an efficient and simplified modeling of the physical effects occurring in the subject. My approach based on a system matrix decomposition, associated to a scatter pre-calculated database method, demonstrated an acceptable time for a daily imaging subject follow-up (∼ 1h), leading to a personalized image reconstruction (Auer et al. 2016).
Auer, B., Rey, C., Bekaert, V., Gallone, J.-M., and El Bitar, Z. (2016). "Implementation of a pre-calculated database approach for scatter correction in SPECT." Biomed. Phys. Eng. Express, 2.

Kajal Aggarwal

(50% CNRS / 50% Région)
Development of a Preclinical PET system and investigation on the parameters limiting its performance in spatial and temporal resolution.

Positron Emission Tomography (PET) is a nuclear imaging modality that provides in vivo measurements of the spatial distribution of the compounds labeled with a positron emitting radionuclide. Recently, the ongoing research has two major goals, firstly to improve the Time-Of-Flight (TOF) of the clinical PET system and secondly to combine PET with Magnetic Resonance Imaging (MRI), as a new tool for multimodal imaging, to study the functional processes.

My thesis work is divided into two major steps. The first step is to participate in the development of a Preclinical PET system and to evaluate its performance in terms of instrinsic spatial resolution, Energy resolution, Signal-to-Noise Ratio (SNR) and timing resolution. The second phase of the thesis work is to investigate the parameters limiting the performance of the pre-clinical PET in the scope of above mentioned factors and to work on these parameters leading to improved spatial and temporal resolution of the PET system.

Nastassja Muller

(Chef de clinique)
Caractérisation par imagerie métabolique par Tomographie par Emission de Positon de la réponse tumorale après irradiation proton chez le petit animal.

Mon projet d’étude est de caractériser en imagerie métabolique par Tomographique par Emission de Positon (TEP) la réponse tumorale à la protonthérapie chez le petit animal. La lignée cellulaire inoculée au petit animal par injection sous-cutanée est une lignée cellulaire tumorale humaine isolée à partir du liquide d’ascite d’un patient porteur d’un adénocarcinome hépatique. Les caractéristiques tumorales que nous souhaiterions évaluer par imagerie métabolique après irradiation sont le métabolisme glucidique, la prolifération et l’hypoxie. Pour cela nous avons fait le choix d’utiliser différents radiotraceurs TEP : le 18F-FDG pour le métabolisme glucidique et le 18F-FLT pour la prolifération. L’hypoxie sera marquée par le 18F-MISO ou le 18F-FAZA. La caractérisation métabolique de la tumeur est réalisée avant irradiation et à différents délais après irradiation. Le but est de déterminer d’une part si les radiotraceurs permettent de visualiser la réponse tumorale précoce et tardive, et d’autre part s’ils permettent de déterminer si la dose délivrée à la tumeur au cours de l’irradiation est adaptée ou insuffisante (non-réponse, réponse partielle, rechute précoce). Nous souhaiterions aussi déterminer une éventuelle potentialisation de la radiothérapie par un traitement chimiothérapeutique par Topotécan.

Truong Nguyen-Pham

(50% CNRS / 50% Région)

abstract coming soon