M.G. Bisogni

Università di Pisa, Pisa, Tuscany, Italy

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Publications (120)89.29 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A detector based on a pixellated scintillator crystal coupled on two opposite sides to Silicon Photomultiplier (SiPM) strips is presented. In one direction the width of the SiPM strips matches the crystal pitch, while in the other direction the strip length is equal to the crystal pitch times the number of pixels in a row. The SiPM strips on one side are orthogonal to the strips on the other side. The crystal position can be identified using a row-column coding method. As a proof of concept, a small prototype using an array of 8 × 8 LYSO crystals, each one 1.5 mm × 1.5 mm × 10 mm in dimensions, has been built. The crystal is coupled on both sides to monolithic matrices composed of 8 SiPM strips, each one 1.5 mm wide (pitch) and 12 mm long by means of silicon grease. SiPMs strips have been obtained connecting in parallel single pixels belonging to a monolithic matrix, where each pixel has the same pitch of the scintillating crystal coupled to it. This arrangement allows a reduction from N2 to 2N of the number of analog channels needed to read-out the entire crystal array. Furthermore, this method provides the information about the Depth of Interaction of the primary particles impinging on the detector. The results of the prototype characterization in terms of energy and Depth Of Interaction resolution capabilities are presented here.
    Journal of Instrumentation 08/2014; 9(08):P08007. · 1.66 Impact Factor
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    ABSTRACT: The 4DM-PET experiment aims to develop an innovative detector module for PET applications. The device is composed of a continuous LYSO scintillator crystal coupled to two SiPM matrices on its top and bottom surfaces. The peculiarity in using a continuous crystal is the ability to reconstruct the Depth of Interaction of the 511 keV photons generated by the annihilation of the positrons emitted by the radiotracer. A first small prototype module has been built. It is composed of a LYSO crystal, 20×20×10 mm3 coupled on larger surfaces with arrays of SiPMs (4×4 pixel, 4×4 mm2 each). The lateral faces of the crystal slab are black painted to avoid reflection of light. The detector is read by custom designed Front-End ASICs. We have scanned the detector in the three coordinates with pencil beams produced by collimated radioactive sources in order to investigate the module spatial resolution capabilities. The results achieved in terms of Depth of Interaction (DOI) reconstruction and Point Spread Function (PSF) at different positions on the detector surface are presented.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 12/2013; · 1.14 Impact Factor
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    ABSTRACT: We investigate the potential for extracting DOI information from reading out the light distribution along two (or three) surfaces of a discrete crystal PET detector array. The concept was investigated using both Monte Carlo (GEANT4) simulations and measurements. The crystal array was composed of a 1×6 array of 4×4×22 mm3 LYSO crystals optically coupled with meltmount (N=1.7). One or two of the 4×22 mm2 sides were optically coupled to a linear array of SiPM sensors (lateral SiPMs), as was one of the 4×24 mm2 sides (backend SiPMs.) The other sides of the array were covered with reflective material. A coincidence collimated point flux was collected at regular intervals along the DOI axis of each of the six crystals. The light response function was determined for each crystal versus DOI. The simulated and experimentally measured light response functions had similar shapes. A combination of simulated and measured data analysis was used to investigate the possibility of reducing the number of lateral SiPMs. DOI positioning was excellent for the two crystals nearest the lateral SiPM arrays and for the 10 mm closest to the backend SiPM array but degraded in the two center crystals. Estimated spatial resolution was below 5 mm in 90% of the array when using the backend and one lateral array, and less than 4.5 mm throughout the array when using at least two SiPMs from both lateral arrays.
    IEEE Nuclear Science Symposium and Medical Imaging Conference; 10/2013
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    ABSTRACT: It has already been shown how the shape of the current pulse produced by a SiPM in response to an incident photon is sensibly affected by the characteristics of the front-end electronics (FEE) used to read out the detector. When the application requires to approach the best theoretical time performance of the detection system, the influence of all the parasitics associated to the coupling SiPM–FEE can play a relevant role and must be adequately modeled. In particular, it has been reported that the shape of the current pulse is affected by the parasitic inductance of the wiring connection between SiPM and FEE. In this contribution, we extend the validity of a previously presented SiPM model to account for the wiring inductance. Various combinations of the main performance parameters of the FEE (input resistance and bandwidth) have been simulated in order to evaluate their influence on the time accuracy of the detection system, when the time pick-off of each single event is extracted by means of a leading edge discriminator (LED) technique.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2013; · 1.14 Impact Factor
  • Alberto Del Guerra, Maria Giuseppina Bisogni
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    ABSTRACT: The development of radiation detectors in the field of nuclear and particle physics has had a terrific impact in medical imaging since this latter discipline took off in late '70 with the invention of the CT scanners. The massive use in Nuclear Physics and High Energy Physics of position sensitive gas detectors, of high Z and high density scintillators coupled to Photomultiplier (PMT) and Position Sensitive Photomultipliers (PSPMT), and of solid state detectors has triggered during the last 30 years a series of novel applications in Medical Imaging with ionizing radiation. The accelerated scientific progression in genetics and molecular biology has finally generated what it is now called Molecular Imaging. This field of research presents additional challenges not only in the technology of radiation detector, but more and more in the ASIC electronics, fast digital readout and parallel software. In this paper we will try to present how Nuclear Physics/High Energy Physics and Medical Imaging have both benefited by the cross-fertilization of research activities between the two fields and how much they will take advantage in the future.
    06/2013;
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    ABSTRACT: Positron emission tomography (PET) is a clinical and research tool for in vivo metabolic imaging. The demand for better image quality entails continuous research to improve PET instrumentation. In clinical applications, PET image quality benefits from the time of flight (TOF) feature. Indeed, by measuring the photons arrival time on the detectors with a resolution less than 100 ps, the annihilation point can be estimated with centimeter resolution. This leads to better noise level, contrast and clarity of detail in the images either using analytical or iterative reconstruction algorithms. This work discusses a silicon photomultiplier (SiPM)-based magnetic-field compatible TOF-PET module with depth of interaction (DOI) correction. The detector features a 3D architecture with two tiles of SiPMs coupled to a single LYSO scintillator on both its faces. The real-time front-end electronics is based on a current-mode ASIC where a low input impedance, fast current buffer allows achieving the required time resolution. A pipelined time to digital converter (TDC) measures and digitizes the arrival time and the energy of the events with a timestamp of 100 ps and 400 ps, respectively. An FPGA clusters the data and evaluates the DOI, with a simulated z resolution of the PET image of 1.4 mm FWHM.
    IS&T/SPIE Electronic Imaging; 02/2013
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    ABSTRACT: The importance of a high-quality hybrid imaging, providing morphological and functional information with only one acquisition session, is widely acknowledged by the scientific community. The historical limitations to the quality of PET images are related to the unsatisfactory measurement of the depth of interaction (DOI) in the crystals and of the time of flight (TOF), that cause a parallax error and an unfavorable signal to background condition in the image reconstruction process, respectively. The 4DMPET project is developing a high performance PET block-detector featuring 4D image reconstruction capabilities. The detector module is based on a fast scintillating continuous crystal coupled on both sides to arrays of Silicon PhotoMultipliers (SiPM). The SiPMs collect the scintillation light and provide the trigger signal, the time and the energy released in the crystal at the pixel level. The photon depth of interaction (DOI) is reconstructed by measuring the cluster size asymmetry on the two faces of the crystal, thus obtaining a comparable spatial resolution in the three coordinates and removing the parallax error. The event position along the line of response can be measured with high precision by means of TOF techniques. We discuss the module design concept and the results of the detailed Monte Carlo detector simulation, which inspire the architectural solutions selected for the layout and the front-end The expected resolution for 3D spatial coordinates of the interaction point in the crystal (1 mm) and the TOF (about 110 ps) would provide a substantial improvement of the image quality. 4DMPET aims at building a prototype block detector demonstrating that the proposed layout meets the expected performance and is suitable for designing a detector focused on a specific application.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2013; 702:6–9. · 1.14 Impact Factor
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    ABSTRACT: Positron emission tomography (PET) is a molecular imaging technique that provides images of physiological processes inside the body. In clinical applications, PET image quality benefits from the time of flight (TOF) feature. This is based on measuring the difference in the arrival times of couples of nearly collinear photons generated during the PET exam on a detector ring with a resolution less than 100 ps. In this scenario, a time to digital converter (TDC) can be used for the read out of the detectors to provide the photon arrival time. If matrices of Silicon Photomultipliers are used as photodetectors, multichannel topology and real time noise rejection capability are strongly required in the design of the converter along with good linearity. We present an innovative TDC architecture which is suitable for TOF PET applications.
    Time-to-Digital Converters (NoMe TDC), 2013 IEEE Nordic-Mediterranean Workshop on; 01/2013
  • Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 09/2012; · 1.14 Impact Factor
  • Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 09/2012; · 1.14 Impact Factor
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    ABSTRACT: A prototype of a high resolution small animal PET scanner with continuous LYSO crystals coupled to SiPM matrices has been developed. Initial tomographic images of point-like sources have been obtained with a spatial resolution of 0.7±0.2 mm FWHM using crystals with 5 mm and 10 mm thickness. The next step in the prototype development is to improve the scanner performance. From the instrumentation point of view, a slight misalignment of the detector heads has been identified as well as a malfunctioning in the ADC that leads to a degraded time resolution. In addition, a GEANT4 simulation of one detector head has been implemented including generation and transportation of optical photons for a better understanding of its response and to predict its performance in different conditions. Squared and tapered crystals geometries have been simulated. Simulated data have been compared to experimental data, showing good agreement.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE; 01/2012
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    ABSTRACT: We are investigating the performances of a data acquisition system for Time of Flight PET, based on LYSO crystal slabs and 64 channels Silicon Photomultipliers matrices (1.2 cm2 of active area each). Measurements have been performed to test the timing capability of the detection system (SiPM matices coupled to a LYSO slab and the read-out electronics) with both test signal and radioactive source.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2012; 695:210-212. · 1.14 Impact Factor
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    ABSTRACT: Silicon Photomultipliers are used in many new generation PET block detectors. High granularity pixel SiPMs allow a high precision measurement of the photon interaction coordinates along the crystal surface. In order to further improve the resolution it is necessary to measure the photon Depth of Interaction (DOl), so as to reduce the parallax error in the Line of Response reconstruction. An innovative technique for DOl determination is proposed and tested. Measurements are made with a 2 cm × 2 cm × 1 cm LYSO slab with readout on the front and back large sides by means of two 4 × 4 square SiPM pixel matrices of 5 mm pitch. The data acquisition is based on the new BASIC32 chip read out with an FPGA-based system.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE; 01/2012
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    ABSTRACT: The design of a Positron Emission Tomography detection module capable of working inside a Magnetic Resonant Imaging system is the main objective of the 4D-MPET project. Combining the two imaging technologies offers better soft tissue contrast and lower radiation doses by providing both functional and morphological information at the same time. The proposed detector will feature a three-dimensional architecture based on two tiles of Silicon Photomultipliers coupled to a single LYSO scintillator on both its faces. Silicon Photomultipliers are magnetic-field compatible photo-detectors with a very small size enabling novel detector geometries that allow the measurement of the Depth of Interaction as well as a high detector packing fraction to maximize system sensitivity. Furthermore they can be fabricated using standard silicon technology, have a large gain in the order of 106 and are very fast thus allowing evaluating the Time of Flight. Among the other features of the proposed detection system, the architecture of the innovative readout electronics will be also described which plays a relevant role for the achievement of the desired performance and is based on custom integrated circuits. Simulation results of the whole system show good performance in terms of time and spatial resolution: a timestamp of 100 ps is the ultimate performance achievable with the use of a double threshold technique along with fast electronics. Time over threshold is exploited to provide the energy information with a bin size of 400 ps. Moreover, a z resolution of 1.4 mm Full Width at Half Maximum can be achieved. The proposed detector can also be exploited in other tracking applications, such as High Energy Physics and Astrophysics.
    Journal of Instrumentation 01/2012; · 1.66 Impact Factor
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    ABSTRACT: A PET imaging system demonstrator based on LYSO crystal arrays coupled to SiPM matrices is under construction at the University and INFN of Pisa. Two SiPM matrices, composed of 8×8 SiPM pixels, and 1,5mm pitch, have been coupled one to one to a LYSO crystals array and read out by a custom electronics system. front-end ASICs were used to read 8 channels of each matrix. Data from each front-end were multiplexed and sent to a DAQ board for the digital conversion; a motherboard collects the data and communicates with a host computer through a USB port for the storage and off-line data processing. In this paper we show the first preliminary tomographic image of a point-like radioactive source acquired with part of the two detection heads in time coincidence.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2012; · 1.14 Impact Factor
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    ABSTRACT: It is generally recognized that the main factors affecting the timing accuracy of a typical γ-ray detection system based on SiPM's coupled to fast scintillators are related to the statistical properties of the scintillation light, to the parameters of the SiPM and to the performance of the front-end electronics used to read out the detectors. In our study, Geant4 Monte Carlo simulations have been exploited to reproduce the statistical characteristics of the photon emission from the scintillator in response to the photoelectric absorption of a γ-ray. Each Monte Carlo trial provides the incidence times of the emitted photons on the surface of the detector. A comprehensive electrical model of the SiPM coupled to the front-end electronics allows finding the waveform of the elementary current pulses produced by each single photon which triggers the avalanche breakdown in a micro-cell of the SiPM, taking into account also the interconnection parasitics. Combining the available information for each Monte Carlo trial, the overall pulse waveform, obtained in response to the photoelectric interaction of a y-ray in the scintillator, is reconstructed. In case a leading edge discriminator is used to generate the signal which marks the arrival of the event, it is possible to study the accuracy of this timing signal as a function of the threshold level, considering also the contribution from the electronic noise of the front-end. Using this procedure, it is possible to distinguish the contribution of each individual parameter affecting the timing accuracy of the detection system and, in particular, to obtain useful indications for an effective choice of the specifications of the front-end electronics.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE; 01/2012
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    ABSTRACT: Scintillators suitable for PET applications must be characterized by a high efficiency for gamma-ray detection, determined by a high density and atomic number of the crystal; a fast light signal that allows to achieve a good time resolution and to cope with high counting rates; a high light yield for a good energy and time resolution; a good linearity of the light output as a function of the energy to preserve the intrinsic energy resolution of the scintillator. Recently developed LSO:Ce scintillators, co-doped with Ca, have been produced by the University of Tennessee group. They are characterized by the improved performance of most the above-mentioned characteristics. The crystals, initially tested with PMTs, showed a higher light output, faster light pulse, improved energy resolution and reduced afterglow, as compared to the standard LSO:Ce crystals. Even though the PMTs still represent the gold standard photodetectors, the recently available SiPMs are now valid candidate to replace PMTs in the next generation of PET scanners thanks to their compactness, high spatial resolution performances, low bias operating voltage and, most important for combined PET/MRI systems, insensitivity to static and RF fields. In this work we present the performance of Ca co-doped LSO:Ce samples coupled to SiPMs and PMTs. In particular we have assessed their performances by evaluating the energy and time resolution.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2011; 628(1):423-425. · 1.14 Impact Factor
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    ABSTRACT: In this work we present a comparison of different methods for reconstructing the position of the events detected by gamma cameras with small Field of View. This task was completed within a project aimed to the development of an ultra high resolution, MR compatible PET detector camera head based on SiPM detector. It is well known that the spatial resolution deteriorates and the displacement error (defined as the deviation of the reconstructed position from the true position) increases at the edges of the detector. Here we investigate the possibility of improving the detector performance by using different reconstruction methods. The usual algorithm based on the barycenter fails to track the true position near the edges of the detector. We implemented and tested four different algorithms: the classic barycenter, a modified barycenter method where we consider not the charge collected, but the charge squared (named ``barycenter squared''), an algorithm based on the estimation of the skewness of the distribution of the light (``skewness''), and finally a method based on the minimization of the difference between the distribution of light and a suitable fitting function (``Newton''). It turns out that the use of reconstruction algorithms different from the classic barycenter can help to improve the performance of the system. In particular, the reconstruction error improves, especially at the edges of the detector. Our simulations show that it is feasible to get submillimeter planar spatial resolutions at the center of the detector and of about 1 mm at the edges of the detector.
    Journal of Instrumentation 01/2011; 6(01):C01030. · 1.66 Impact Factor
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    ABSTRACT: A first prototype of a high resolution small animal PET scanner based on continuous LYSO scintillator crystals and silicon photomultiplier matrices has been developed at IFIC-Valencia, in collaboration with the University of Pisa and INFN Pisa. The prototype consists of two detector heads attached to a rotating stage. Each head is composed of a continuous 12 mm × 12 mm × 5 mm LYSO crystal painted white, coupled to a monolithic SiPM matrix. The matrices, developed at FBK-irst, are composed of 8×8 SiPM elements of 1.5 mm×1.4 mm size in a common substrate. The full characterization of the detector heads with different types of crystals has been carried out, and a method for determining the interaction position of the gamma-rays in the crystals has been successfully employed. Tomographic data have been acquired with the prototype, and images of different source distributions have been reconstructed with the Maximum Likelihood Expectation Maximization algorithm (MLEM). A FWHM close to 1 mm is obtained for one and two point-like sources.
    01/2011;
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    ABSTRACT: A small Positron Emission Tomography demonstrator based on LYSO slabs and Silicon Photomultiplier matrices is under construction at the University and INFN of Pisa.
    01/2011;

Publication Stats

332 Citations
89.29 Total Impact Points

Institutions

  • 1998–2014
    • Università di Pisa
      • • Department of Physics "E.Fermi"
      • • Department of Information Engineering
      Pisa, Tuscany, Italy
  • 1997–2009
    • Università degli Studi di Sassari
      Sassari, Sardinia, Italy
  • 2002
    • Università degli Studi di Siena
      Siena, Tuscany, Italy
  • 2001
    • University of Naples Federico II
      • Department of Physical Sciences
      Portici, Campania, Italy
  • 1999
    • INFN - Istituto Nazionale di Fisica Nucleare
      Frascati, Latium, Italy
    • University of Florence
      Florens, Tuscany, Italy
  • 1996
    • University of Glasgow
      • School of Physics and Astronomy
      Glasgow, SCT, United Kingdom