A detection system of the conventional PET tomograph is set-up to record data from annihilation into two photons with energy of 511 keV, and it gives information on the density distribution of a ...radiopharmaceutical in the body of the object. In this paper we explore the possibility of performing the three gamma photons imaging based on ortho-positronium annihilation, as well as the possibility of positronium mean lifetime imaging with the J-PET tomograph constructed from plastic scintillators. For this purposes simulations of the ortho-positronium formation and its annihilation into three photons were performed taking into account distributions of photons' momenta as predicted by the theory of quantum electrodynamics and the response of the J-PET tomograph. In order to test the proposed ortho-positronium lifetime image reconstruction method, we concentrate on the decay of the ortho-positronium into three photons and applications of radiopharmaceuticals labeled with isotopes emitting a prompt gamma. The proposed method of imaging is based on the determination of hit-times and hit-positions of registered photons which enables the reconstruction of the time and position of the annihilation point as well as the lifetime of the ortho-positronium on an event-by-event basis. We have simulated the production of the positronium in point-like sources and in a cylindrical phantom composed of a set of different materials in which the ortho-positronium lifetime varied from 2.0 ns to 3.0 ns, as expected for ortho-positronium created in the human body. The presented reconstruction method for total-body J-PET like detector allows to achieve a mean lifetime resolution of 40 ps. Recent positron annihilation lifetime spectroscopy measurements of cancerous and healthy uterine tissues show that this sensitivity may allow to study the morphological changes in cell structures.
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 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 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.
A novel whole-body positron emission tomography (PET) system based on plastic scintillators is developed by the J-PET Collaboration. It consists of plastic scintillator strips arranged axially in the ...form of a cylinder, allowing the cost-effective construction of the total-body PET system. In order to determine the properties of the scanner prototype and optimize its geometry, advanced computer simulations were performed using the GATE (Geant4 application for tomographic emission) software. The spatial resolution, sensitivity, scatter fraction and noise equivalent count rate were estimated according to the National Electrical Manufacturers Association norm, as a function of the length of the tomograph, the number of detection layers, the diameter of the tomographic chamber and for various types of applied readout. For the single-layer geometry with a diameter of 85 cm, a strip length of 100 cm, a cross-section of 4 mm × 20 mm and silicon photomultipliers with an additional layer of wavelength shifter as the readout, the spatial resolution (full width at half maximum) in the centre of the scanner is equal to 3 mm (radial, tangential) and 6 mm (axial). For the analogous double-layer geometry with the same readout, diameter and scintillator length, with a strip cross-section of 7 mm × 20 mm, a noise equivalent count rate peak of 300 kcps was reached at 40 kBq cc−1 activity concentration, the scatter fraction is estimated to be about 35% and the sensitivity at the centre amounts to 14.9 cps kBq−1. Sensitivity profiles were also determined.
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 formulae for time resolution. The proposed method is validated using signals registered by means of the single detection unit of the J-PET tomograph built from a 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.
Time Calibration of the J-PET Detector Skurzok, M.; Silarski, M.; Alfs, D. ...
Acta physica Polonica, A,
11/2017, Letnik:
132, Številka:
5
Journal Article
The Bonikowo Reef occurs in the central part of the Zechstein Limestone Basin in western Poland and was growing on the topmost edges of tilted blocks and/or on the top of uplifted horsts of the ...Brandenburg-Wolsztyn-Pogorzela High.Its size is ca.1.6 km2.The Bonikowo Reef shows the thickest reef section (90.5 m) recorded in the High.The Zechstein Limestone unit is represented mostly by limestones,often thoroughly recrystallized,although the macrotextures and biota of the boundstone are identifiable in most cases.The drillcore section is a mixture of boundstones (microbial and bryozoan),wackestones,packstones and grainstones,which often co-occur.The δ13C and δ18O values for both calcite (avg.3.8 ± 0.8‰ and -3.4 ± 1.7‰,respectively) and dolomite (avg.3.5 ± 0.7‰ and-5.2 ± 1.3‰,respectively) are transitional between the values previously reported for condensed sequences of the basinal facies and larger reef complexes.The biofacies of the Bonikowo Reef are very similar to those recognized in other reefs of the Brandenburg-Wolsztyn-Pogor-zela High,which owe their origin to the destruction of bryozoan boundstones.The biota composition is typical and characteristic of other Zechstein Limestone reefs.However,the Bonikowo Reef demonstrates the importance of microbialites,laminar and nodose encrustations,in the growth and cohesion of the Zechstein Limestone reefs.Such encrustations abound within the Zechstein Limestone although,in many cases,the real nature of the encrustations is difficult to ascertain.These laminated encrustations show great similarity to Archaeolithoporella that is one of the most important Permian reefbuilding organisms.The encrustations considered to represent Archaeolithoporella were also previously recorded in the Zechstein Limestone of western Poland and in its stratigraphic equivalent,the Middle Magnesian Limestone of Northeast England.The lower part of the sequence shows great biofacies variability that reflects common environmental changes.The major part of the section is represented by slope deposits grading upward into the reef,which reflects the prograding nature of reef margin.The progradation rate for the Bonikowo Reef is estimated at 400 m/My.
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