The TRIMAGE project aims at developing a braindedicated PET/MR system able to perform simultaneous PET and MR acquisitions for application in schizophrenia. Both PET and MR components have been designed in this project. The PET component consists of a full ring with 18 sectors each comprising three square detector modules. The modules are based on duallayer staggered matrices of LYSO crystals read out by silicon photomultipliers. The FOV of the combined PET/MR/EEG system has an inner diameter of 260 mm and an axial extension of 160 mm. This paper describes in full detail the final version of the PET detectors and the related electronics. It also reports on the preliminary performance of a pair of sectors in terms of pixel resolvability index (RI), energy resolution, singles count rate capability and coincidence time resolution (CTR). The procedures used for the optimization and calibration of PET detector are described. Results demonstrate the pixel/layer identification performance with a RI of about 0.2 while the energy resolution resulted in 20% and 22% FWHM for the bottom and top layer, respectively. The maximum singles count rate of a PET detector is about 700 kcps and the CTR of two sectors is 515 ps.
Objective. Monolithic scintillator crystals coupled to silicon photomultiplier (SiPM) arrays are promising detectors for PET applications, offering spatial resolution around 1 mm and depth-of-interaction information. However, their timing resolution has always been inferior to that of pixellated crystals, while the best results on spatial resolution have been obtained with algorithms that cannot operate in real-time in a PET detector. In this study, we explore the capabilities of monolithic crystals with respect to spatial and timing resolution, presenting new algorithms that overcome the mentioned problems. Approach. Our algorithms were tested first using a simulation framework, then on experimentally acquired data. We tested an event timestamping algorithm based on neural networks which was then integrated into a second neural network for simultaneous estimation of the event position and timestamp. Both algorithms are implemented in a low-cost field-programmable gate array that can be integrated in the detector and can process more than 1 million events per second in real-time. Results. Testing the neural network for the simultaneous estimation of the event position and timestamp on experimental data we obtain 0.78 2D FWHM on the (x, y) plane, 1.2 depth-of-interaction FWHM and 156 coincidence time resolution on a 25 mm × 25 mm × 8 mm × LYSO monolith read-out by 64 3 mm × 3 mm Hamamatsu SiPMs. Significance. Our results show that monolithic crystals combined with artificial intelligence can rival pixellated crystals performance for time-of-flight PET applications, while having better spatial resolution and DOI resolution. Thanks to the use of very light neural networks, event characterization can be done on-line directly in the detector, solving the issues of scalability and computational complexity that up to now were preventing the use of monolithic crystals in clinical PET scanners.
In hadron therapy, the accelerated ions, interacting with the body of the patient, cause the fragmentation of both projectile and target nuclei. The fragments interact with the human tissues depositing energy both in the entrance channel and in the volume surrounding the tumor. The knowledge of the fragments features is crucial to determine the energy amount deposited in the human body, and - hence - the damage to the organs and to the tissues around the tumor target. The FOOT (FragmentatiOn Of Target) experiment aims at studying the fragmentation induced by the interaction of a proton beam (150-250 MeV/n) inside the human body. The FOOT detector includes an electronic setup for the identification of Z ≥ 3 fragments integrated with an emulsion spectrometer to measure Z ≤ 3 fragments. Charge identification by nuclear emulsions is based on the development of techniques of controlled fading of the particle tracks inside the nuclear emulsion, that extend the dynamical range of the films developed for the tracking of minimum ionising particles. The controlled fading strongly depends on temperature, relative humidity and treatment duration. In this study the performances in terms of charge separation of proton, helium and carbon particles, obtained on a batch of new emulsion films produced in Japan are reported.
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