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Correction de l'atténuation et de la réponse géométrique d'un détecteur en tomographie d'émission sur colis de déchets nucléaires

Raphaël Thierry 1
1 TIMC-GMCAO - Gestes Medico-chirurgicaux Assistés par Ordinateur
TIMC - Techniques de l'Ingénierie Médicale et de la Complexité - Informatique, Mathématiques et Applications, Grenoble - UMR 5525
Abstract : Multiphotonic emission tomography is a non destructive technique applied to the control of radioactive waste drums. The emitted gamma rays are detected on the range [50 keV, 2 MeV] by a hyper pure germanium, of high resolution in energy, which enables to set up a detailed list of radionucleides contained within the drum. From different points of measurement located in a transaxial plane of the drum, the activity distribution is computed by a reconstruction algorithm. An algebraic modelling of the physical process has been developed in order to correct the different degrading phenomenon, in particular the attenuation and the detector geometric response. Attenuation through the materials constituting the barrel is the preponderant phenomena. Its ignorance prevents from accurate activity quantification. Its correction has been realised from an attenuation map obtained by a transmission tomograph. The detector geometric response, introducing a blurring within the detection, is compensated by an analytic model. An adequate modelling of those phenomenon is primordial : it highly contributes on a large scale the image quality and the quantification. The image reconstruction, requiring the resolution of sparse linear system, is realised by iterative algorithms. Due to the "ill-posed" nature of tomographic reconstruction, it is necessary to use regularisation : by introducing an a priori information on the solution, the stabilisation of the methods is carried out. We chose to minimise the Maximum A Posteriori criterion. Its resolution is considered with a half-quadratic regularisation : it permits the preservation of natural discontinuities, and avoids global oversmoothing of the image. It is evaluated on real phantoms and waste drums. Efficient sampling of the data is considered.
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Submitted on : Wednesday, February 18, 2004 - 5:42:36 PM
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Raphaël Thierry. Correction de l'atténuation et de la réponse géométrique d'un détecteur en tomographie d'émission sur colis de déchets nucléaires. Autre [cs.OH]. Université Joseph-Fourier - Grenoble I, 1999. Français. ⟨tel-00004856⟩

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