Développement d'un module de détection phoswich LSO/LuYAP pour le prototype de caméra à positrons ClearPET

The first part of this thesis describes the development of an optimised LSO/LuYAP phoswich detector head for the ClearPET demonstrator positron emission tomograph (PET) dedicated to small animals that is under construction in Lausanne within the Crystal Clear Collaboration. The detector head consists of a dual layer of 8 x 8 LSO and LuYAP crystal arrays coupled to a multi-anode photomultiplier tube (MaPMT). Equalistion of the LSO/LuYAP light collection is obtained through partial attenuation of the LSO scintillation light using a thin aluminium deposit of 20-35 nm on LSO and appropriate temperature regulation of the phoswich head between 30 to 60°C. At 511 keV, typical FWHM energy resolutions of the pixels of a phoswich head amounts to (28±2)% for LSO and (25±2)% for LuYAP. The LSO versus LuYAP crystal identification efficiency is better than 98%. Eighteen detector modules have been mounted on a rotating gantry. Radial and tangential spatial resolutions were measured up to 4 cm from the scanner axis and compared to Monte Carlo simulations using GATE. FWHM spatial resolution ranges from 1.3 mm on axis to 2.6 mm at 4 cm from the axis. Time resolution was measured for several event tagging methods. Pulse shape discrimination methods with an efficiency of 97-99% were developed for LSO/LuAP and LuAP/LuYAP phoswich among these, some are based on neural networks. The second part of this work is devoted to characterisation measurements performed on several recently developed arrays of avalanche photodiodes (APDs) with the perspective of replacing MaPMTs. Their doping profile were estimated from the dependence of capacitance on junction voltage. Quantum efficiency was measured as a function of wavelength in the range of 300-700 nm. Bulk and surface contributions to the dark current were estimated. Gain and excess noise factor were measured as a function of bias voltage. The S8550 APD array produced by Hamamatsu Photonics appears as being the best candidate for an aplication in PET. The last part of this thesis is dedicated to a prospective study performed on S8550 APD arrays coupled to LSO and LuAP crystals. Energy resolution and its contributions as well as time resolution were measured on modules having a single layer of LSO and LuAP crystals. Two staggered LSO/LSO and LSO/LuAP assemblies were evaluated regarding depth of interaction identification efficiency and energy resolution. Finally, a synthesis of the results obtained is presented.

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