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[en] Positron emission tomography (PET) has moved from a distinguished research tool in physiology, cardiology and neurology to become a major tool for clinical investigation in oncology, in cardiac applications and in neurological disorders. Much of the PET accomplishments is due to the remarkable improvements in the last 10 years both in hardware and software aspects. Nowadays a similar effort is made by many research groups towards the construction of dedicated PET apparatus in new emerging fields such as molecular medicine, gene therapy, breast cancer imaging and combined modalities. This paper reports on some recent results we have obtained in small animal imaging and positron emission mammography, based on the use of advanced technology in the field of scintillators and photodetectors, such as Position-Sensitive Detectors coupled to crystal matrices, combined use of scintillating fibers and Hybrid-Photo-Diodes readout, and Hamamatsu flat panels. New ideas and future developments are discussed
[en] A prototype for positron emission mammography is under development within a collaboration of the Departments of Physics of Pisa and Ferrara. The device will be composed of two opposing detectors (parallel plane geometry). The active part of the detector head is constituted by a matrix of scintillators with a small pixel size (2x2 mm2). We have evaluated the possibility to use an array of Position Sensitive PhotoMultiplier Tube (PSPMT mod R8520-C12 from Hamamatsu) for the readout of the scintillation matrix. Two different crystal-PMT coupling techniques have been explored: the results for each method are reported in this work. The overall performance, in terms of efficiency and pixel identification of the final prototype of the detector head are also presented. For future applications the new H8500 (also called the 'flat panel' PMT) has been studied and compared to the R8520 in terms of the imaging performance and other considerations such as cost and geometry. The imaging performance of these tubes is characterized in terms of the pixel image resolution and the peak-to-valley ratio
[en] The development of MRI compatible detectors based on compact solid state photomultipliers has recently led to simultaneous fully integrated PET/MRI systems for human imaging. The PET acquisition design for MRI integration is known to have several additional constraints, including smaller space, electromagnetic compatibility issues and thermal management. The current work presents the PET acquisition architecture that has been developed for the TRIMAGE project, whose aim is to provide a cost effective, commercial grade trimodality PET/MRI/EEG scanner. The TRIMAGE PET component consists of 216 modules of 2.5 cm x 2.5 cm, arranged in 18 rectangular detectors of 5 cm x 15 cm, the latter in the axial direction, to form a full ring of 31 cm diameter. Each module consists of a staggered dual layer LYSO matrix read out by two arrays of 4 x 8 SiPMs and an ASIC. The detector board hosts a low-power low-end FPGA that performs pixel identification, energy calibration and handles the communication between the ASICs and the motherboard, which is located in proximity of the scanner. Data is streamed using high-density shielded cables and high-speed LVDS transmission to 9 low-end SoC FPGAs and from there to a central mainboard where coincidences and events statistics are processed. Coincidence data is finally transmitted to a host PC for image reconstruction. The proposed architecture and technological solutions will be presented and discussed.
[en] The TRIMAGE consortium aims to develop a multimodal PET/MR/EEG brain scanner dedicated to the early diagnosis of schizophrenia and other mental health disorders. The PET component features a full ring made of 18 detectors, each one consisting of twelve 8x8 Silicon PhotoMultipliers (SiPMs) tiles coupled to two segmented LYSO crystal matrices with staggered layers. In each module, the crystals belonging to the bottom layer are coupled one to one to the SiPMs, while each crystal of the top layer is coupled to four crystals of the bottom layer. This configuration allows to increase the crystal thickness while reducing the depth of interaction uncertainty, as photons interacting in different layers are expected to produce different light patterns on the SiPMs. The PET scanner will implement the pixel/layer identification on a front-end FPGA. This will allow increasing the effective bandwidth, setting at the same time restrictions on the complexity of the algorithms to be implemented. In this work two algorithms whose implementation is feasible directly on an FPGA are presented and evaluated. The first algorithm implements a method based on adaptive thresholding, while the other uses a linear Support Vector Machine (SVM) trained to distinguish the light pattern coming from two different layers. The validation of the algorithm performance is carried out by using simulated data generated with the GAMOS Monte Carlo. The obtained results show that the achieved accuracy in layer and pixel identification is above the 90% for both the proposed approaches.
[en] A novel x-ray source for mammography application is being investigated. Quasimonochromatic x rays have been produced via Bragg diffraction with a W-anode x-ray tube and a graphite mosaic crystal array. The system provides 18 keV x rays with an energy resolution ΔE/E≅0.12. A thorough analysis of the spatial resolution of the system has been performed in order to understand and quantify the effect of the introduction of an active optical element such as a mosaic crystal in the x-ray path. The focal spot of the source and its emission properties have been studied by using the slit camera method. Experiments have shown that the introduction of a mosaic crystal in the optical path modifies the resolution properties of the Bragg diffraction-based radiography system. Along the direction perpendicular to the diffraction plane the resolution properties of the imaging system mainly depend on the x-ray tube focal spot size and position. Along the diffraction plane the focal spot size depends on mosaic characteristics and on the geometrical setup. Hence, it could be modified by setting the appropriate experimental conditions
[en] This review describes the properties of available and emerging radiation detector and read-out technologies and discusses how they may affect PET scanner performance. After a general introduction, there is a section in which the physical properties of several different detector scintillators are compared. This is followed by a discussion of recent advances in read-out electronics. Finally, the physical performance of the several commercial PET scanners is summarized. (orig.)
[en] The success of PET systems for dedicated applications such as small animal and breast cancer imaging is largely due to the continuous development of high-resolution, high sensitivity instrumentation for gamma ray detection. This paper reports on some recent advances in the technology together with a brief review of the state-of-the-art of PET systems in these fields. A brief overview of the near-future perspectives is also presented
[en] The design of CMOS front-end electronics suitable for Silicon Photo-Multipliers (SiPM) is described in this paper, starting with the specification of an accurate electrical model of the detector and its experimental validation. A novel current-mode solution is proposed for the preamplifier and the discriminator, to cope with the large dynamic range and the extremely fast rise time of the detector signal. Experimental results achieved from front-end prototypes designed according to this current-mode approach demonstrate its effectiveness: dynamic range of the order of 50 pC and timing accuracy of the electronics alone of about 30 ps have been measured.
[en] Molecular imaging is an emerging field of research for the investigation of biological processes occurring at cellular level. This new field could help the understanding of human diseases by studying animal models. To accomplish this ambitious program, the development of novel high-performance imaging instruments such as small animal PET holds a fundamental role. This paper reports on the present state of the art in small animal PET scanners together with a spotlight view on future technologies for next generation instruments
[en] During the last decade we have observed a growing interest in in-vivo imaging techniques for small animals. This is due to the necessity of studying biochemical processes at a molecular level for pharmacology, genetic, and pathology investigations. Among the various 'molecular imaging' techniques Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) have represented a valuable approach in such field. On the shadow of the successful application of combined PET-CT scanners in the clinical environment, multi-modality techniques have been recently transferred to small animal scanners. This paper reports on some recent advances in small animal PET, SPECT and CT scanners. An overview of the near future perspectives is also presented