Characterization studies and prototyping for a novel Positron Emission Tomography detector

Daniele Cortinovis
Apr 2016

Thesis Type:

This thesis deals with a characterization study of single components and the following integration in a prototype PET detector for the EndoTOFPET-US system, a novel multimodal medical imaging tool. Combining PET and ultrasound (US), EndoTOFPET-US will allow the investigation of newly developed specic biomarkers for pancreatic and prostate tumors, and therefore improving the diagnosis capability. The EndoTOFPET-US system consists of an external PET plate in coincidence with a PET head mounted on an endoscopic US probe. The external PET detector has 4096 channels, each made of a silicon photomultiplier (SiPM) coupled to a scintillating crystal. A dedicated setup has been developed in order to characterize and assess the quality of each SiPM in a fast, reliable and automatic way. The precise determination of the SiPM properties is critical for the optimization of the detector performances. A mass characterization has been performed, obtaining all the relevant parameters for more than 4000 SiPMs and excluding few of them from the detector assembly due to the excessive noise. A similar mass characterization has been performed also on the combined system of SiPMs glued to the scintillating crystals. The light output for the 511 keV gamma has been measured for every detector channel: the average value obtained for all the 4096 channels allows to reach the demanding coincidence time resolution of 200 ps FWHM. Due to the limited number of pixels in the SiPM, the detector response is not linear to the energy deposited in the scintillator. A method has been derived to implement the energy calibration for all the channels, and therefore derive the energy resolution for the 511 keV gamma. The mean value obtained, about 13%, is enough for effective Compton rejection and it is within the detector specications. After the quality assurance of the single components, the integration of two detector modules with the dedicated readout electronics has been tested. A rst PET image of a double point radioactive source has been obtained. Finally, all the detector modules have been assembled in the rst external plate prototype. After the functional tests and the energy calibration of the detector, the rst coincidence data have acquired with a provisional PET-US probe. Then, this EndoTOFPET-US prototype has been commissioned on phantoms, achieving the rst PET images for a free-hand PET system, an essential step before the incoming pre-clinical tests.

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