780 research outputs found
A novel method for calibration and monitoring of time synchronization of TOF-PET scanners by means of cosmic rays
All of the present methods for calibration and monitoring of TOF-PET scanner
detectors utilize radioactive isotopes such as e.g. Na or Ge,
which are placed or rotate inside the scanner. In this article we describe a
novel method based on the cosmic rays application to the PET calibration and
monitoring methods. The concept allows to overcome many of the drawbacks of the
present methods and it is well suited for newly developed TOF-PET scanners with
a large longitudinal field of view. The method enables also monitoring of the
quality of the scintillator materials and in general allows for the continuous
quality assurance of the PET detector performance.Comment: 10 pages, 7 figure
Characterization studies of Silicon Photomultipliers and crystals matrices for a novel time of flight PET detector
This paper describes the characterization of crystal matrices and silicon
photomultiplier arrays for a novel Positron Emission Tomography (PET) detector,
namely the external plate of the EndoTOFPET-US system. The EndoTOFPET-US
collaboration aims to integrate Time-Of-Flight PET with ultrasound endoscopy in
a novel multimodal device, capable to support the development of new biomarkers
for prostate and pancreatic tumors. The detector consists in two parts: a PET
head mounted on an ultrasound probe and an external PET plate. The challenging
goal of 1 mm spatial resolution for the PET image requires a detector with
small crystal size, and therefore high channel density: 4096 LYSO crystals
individually readout by Silicon Photomultipliers (SiPM) make up the external
plate. The quality and properties of these components must be assessed before
the assembly. The dark count rate, gain, breakdown voltage and correlated noise
of the SiPMs are measured, while the LYSO crystals are evaluated in terms of
light yield and energy resolution. In order to effectively reduce the noise in
the PET image, high time resolution for the gamma detection is mandatory. The
Coincidence Time Resolution (CTR) of all the SiPMs assembled with crystals is
measured, and results show a value close to the demanding goal of 200 ps FWHM.
The light output is evaluated for every channel for a preliminary detector
calibration, showing an average of about 1800 pixels fired on the SiPM for a
511 keV interaction. Finally, the average energy resolution at 511 keV is about
13 %, enough for effective Compton rejection.Comment: 12 pages, 31 figure
Silicon Photomultipliers (SiPM) as novel photodetectors for PET
Next generation PET scanners should fulfill very high requirements in terms of spatial, energy and timing resolution. Modern scanner performances are inherently limited by the use of standard photomultiplier tubes. The use of Silicon Photomultipliers (SiPMs) is proposed for the construction of a 4D-PET module of 4.8×4.8 cm2 aimed to replace the standard PMT based PET block detector. The module will be based on a LYSO continuous crystal read on two faces by Silicon Photomultipliers. A high granularity detection surface made by SiPM matrices of 1.5 mm pitch will be used for the x–y photon hit position determination with submillimetric accuracy, while a low granularity surface constituted by 16 mm2 SiPM pixels will provide the fast timing information (t) that will be used to implement the Time of Flight technique (TOF). The spatial information collected by the two detector layers will be combined in order to measure the Depth of Interaction (DOI) of each event (z). The use of large area multi-pixel Silicon Photomultiplier (SiPM) detectors requires the development of a multichannel Data Acquisition system (DAQ) as well as of a dedicated front-end in order not to degrade the intrinsic detector capabilities and to manage many channels. The paper describes the progress made on the development of the proof of principle module under construction at the University of Pisa
The Borexino detector at the Laboratori Nazionali del Gran Sasso
Borexino, a large volume detector for low energy neutrino spectroscopy, is
currently running underground at the Laboratori Nazionali del Gran Sasso,
Italy. The main goal of the experiment is the real-time measurement of sub MeV
solar neutrinos, and particularly of the mono energetic (862 keV) Be7 electron
capture neutrinos, via neutrino-electron scattering in an ultra-pure liquid
scintillator. This paper is mostly devoted to the description of the detector
structure, the photomultipliers, the electronics, and the trigger and
calibration systems. The real performance of the detector, which always meets,
and sometimes exceeds, design expectations, is also shown. Some important
aspects of the Borexino project, i.e. the fluid handling plants, the
purification techniques and the filling procedures, are not covered in this
paper and are, or will be, published elsewhere (see Introduction and
Bibliography).Comment: 37 pages, 43 figures, to be submitted to NI
Calculation of time resolution of the J-PET tomograph using the Kernel Density Estimation
In this paper we estimate the time resolution of the J-PET scanner built from
plastic scintillators. We incorporate the method of signal processing using the
Tikhonov regularization framework and the Kernel Density Estimation method. We
obtain simple, closed-form analytical formulas for time resolutions. The
proposed method is validated using signals registered by means of the single
detection unit of the J-PET tomograph built out from 30 cm long plastic
scintillator strip. It is shown that the experimental and theoretical results,
obtained for the J-PET scanner equipped with vacuum tube photomultipliers, are
consistent.Comment: 25 pages, 11 figure
Time resolution of the plastic scintillator strips with matrix photomultiplier readout for J-PET tomograph
Recent tests of a single module of the Jagiellonian Positron Emission
Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips
have proven its applicability for the detection of annihilation quanta (0.511
MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved
resolution is almost by a factor of two better with respect to the current
TOF-PET detectors and it can still be improved since, as it is shown in this
article, the intrinsic limit of time resolution for the determination of time
of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much
lower. As the major point of the article, a method allowing to record
timestamps of several photons, at two ends of the scintillator strip, by means
of matrix of silicon photomultipliers (SiPM) is introduced. As a result of
simulations, conducted with the number of SiPM varying from 4 to 42, it is
shown that the improvement of timing resolution saturates with the growing
number of photomultipliers, and that the 2 x 5 configuration at two ends
allowing to read twenty timestamps, constitutes an optimal solution. The
conducted simulations accounted for the emission time distribution, photon
transport and absorption inside the scintillator, as well as quantum efficiency
and transit time spread of photosensors, and were checked based on the
experimental results. Application of the 2 x 5 matrix of SiPM allows for
achieving the coincidence resolving time in positron emission tomography of
0.170 ns for 15 cm axial field-of-view (AFOV) and 0.365 ns
for 100 cm AFOV. The results open perspectives for construction of a
cost-effective TOF-PET scanner with significantly better TOF resolution and
larger AFOV with respect to the current TOF-PET modalities.Comment: To be published in Phys. Med. Biol. (26 pages, 17 figures
Database and data structure for the novel TOF-PET detector developed for J-PET project
The complexity of the hardware and the amount of data collected during the
PET imaging process require application of modern methods of efficient data
organization and processing. In this article we will discuss the data
structures and the flow of collected data from the novel TOF-PET medical
scanner which is being developed at the Jagiellonian University. The developed
data format reflects: registration process of the gamma quanta emitted from
positron-electron annihilation, Front-End Electronic (FEE) structure and
required input information for the image reconstruction. In addition, the
system database fulfills possible demands of the evolving J-PET project.Comment: 6 p, 3 figs, based on talk given at Symposium on Positron Emission
Tomography, Sept. 19-22, 2013, Jagiellonian University, Krak\'ow PL,
submitted to Bio-Algorithms and Med-System
Scintillator gamma-ray detectors with silicon photomultiplier readouts for high-energy astronomy
Space-based gamma-ray detectors for high-energy astronomy face strict constraints of mass, volume, and power, and must endure harsh operating environments. Scintillator materials have a long history of successful operation under these conditions, and new materials offer greatly improved performance in terms of efficiency, time response, and energy resolution. The use of scintillators in space remains constrained, however, by the mass, volume, and fragility of the associated light readout device, typically a vacuum photomultiplier tube (PMT). Recently developed silicon photomultipliers (SiPMs) offer gains and efficiencies similar to those of PMTs, but with greatly reduced mass and volume, high ruggedness, and no high-voltage requirements. We have therefore been investigating the use of SiPM readouts for scintillator gamma-ray detectors, with an emphasis on their suitability for space- and balloonbased instruments for high-energy astronomy. We present our most recent results, including spectroscopy measurements for lanthanum bromide scintillators with SiPM readouts, and pulse-shape discrimination using organic scintillators with SiPM readouts. We also describe potential applications of SiPM readouts to specific highenergy astronomy instrument concepts
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