Design of the Cherenkov TOF whole-body PET scanner using GATE simulation

Abstract : In this thesis we present the conception and performance studies of the foreseen Cherenkov whole-body positron emission scanner with time-of-flight potential (PECHE project). Our results and conclusions are based on the GATE simulation for following scanner configurations: lead fluoride crystal coupled with micro-channel-plate photomultiplier. This crystal is characterized by high density, transparency for photons in ultraviolet region, and one of the highest photoelectric fraction of about 46%. The chosen photomultiplier is fast, pixelized detector of a large size with a reasonable quantum efficiency, of 25% for 400 nm photon wavelength. Due to these properties, it is possible to create an efficient 511-keV gamma detector with a crystal thickness of the order of 10 mm(one interaction length) and hence minimize the length and dispersion of the photon trajectories, leading to better time resolution. We considered different configurations of the elementary detectors such as crystal thicknesses of 10 and 20 mm, the detector ring diameter of 80 and 90 cm, various options of the crystal coating (black, diffuse white and polished) and two optical interfaces (molecular bonding and conventional assembling with an optical gel). As an optimal configuration we chose a three-ring pet scanner with diameter of the ring 80 cm, 10 mm-thick crystal, protected with lead shielding. Molecular bonding gives better photo-collection if compare with configuration with optical gel. We estimated the potential of the foreseen scanner following the prescription of the NEMA NU 2-2012 standard. In particular, we evaluated the noise equivalent count rate (NECR), spatial resolution, image contrast recovery coefficients versus background variability for the NEMA image quality phantom. Reconstruction of images is done using iterative TOF algorithm implemented in the recently developed open source reconstruction platform CASToR. We concluded that due to an excellent TOF resolution a crystal-based Cherenkov whole-body scanner could achieve performances comparable with a conventional, scintillation-based tomograph. The use of the Cherenkov radiation allows to achieve even much better TOF resolution, but currently it is limited by the transit time spread of the existing photomultipliers, a low number of the detected optical photons, and a limited photon collection efficiency in a crystal. Limitations identified in this study will be addressed in the future development of the improved photodetector using the PbWO₄ radiator, which allows to conceive a whole-body PET scanner with an excellent TOF performance.
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Marharyta Alokhina. Design of the Cherenkov TOF whole-body PET scanner using GATE simulation. Medical Physics [physics.med-ph]. Université Paris-Saclay; Kiïvsʹkij nacìonalʹnij unìversitet imeni Tarasa Ševčenka (Ukraine), 2018. English. ⟨NNT : 2018SACLS279⟩. ⟨tel-02149704⟩

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