A growing interest in the development of dual modality PET/CT scanners prompts the comparative study of numerous scintillators to select the best one, which could be used simultaneously in PET ...detectors working in the pulsing mode and in the CT detectors working in the current mode. In the comparative measurements, done in the same experimental conditions, various samples of BGO, GSO, GSO:Ce, Zr, LGSO, LSO, LYSO, MLS, LaCl 3 , LaBr 3 and CWO scintillators were tested. The measurements covered a determination of the light output, energy resolution, non-proportionality of the light yield, decay times of the light pulses and for the selected crystals their time resolution for 511 keV annihilation quanta. Moreover, a comparative study of afterglow, induced by 60 keV gamma-rays from a strong 241 Am source (13.9 GBq), was done in the second range of time. The LSO-like crystals are the best in the PET scanners application. However, they do not fit to the CT requirements, due to a high afterglow. The studies conclude that besides of the well known BGO, only GSO:Ce and most likely LaBr 3 might be considered for the simultaneous PET/CT detector
The performance of multi pixel photon counters (MPPC) of 3 mm × 3 mm size, with 14400 and 3600 pixels, were studied by means of the signal from a laser light pulser and using the 3 mm × 3 mm × 20 mm ...LSO pixel scintillator. Special attention was paid to measure number of fired pixels, generated by the light of pulser and that of the LSO crystal, using a direct method of a comparison of the light peak position in the pulse height spectrum with that of the single photoelectron. The tests of the LSO crystal showed 1550 ± 80 fired pixels per MeV in the MPPC with 14400 pixels assuring a good linearity of the response up to about 1 MeV energy of gamma rays absorbed in the LSO crystal. Energy resolution of 14.8% for 662 keV gamma rays from 137 Cs source and a time resolution of about 850 ps for 511 keV annihilation quanta were limited by a rather low number of the fired pixels compared to the number of photoelectrons in photomultipliers.
Recently, a silicon photomultiplier (SiPM) became one of the strongest candidates for application in PET–MR or SPECT–MR dual-modality scanners. However, optimization of the scintillation detectors ...with SiPM light readout requires different approach than in the case of classic photomultipliers. The finite number of micro-cells in a SiPM creates nonlinear response for high number of incident photons. Moreover, the size and total number of micro-cells defines fill factor, which in turn affects the photon detection efficiency (PDE). Response of SiPMs is also highly sensitive to bias voltage causing changes in PDE and excess noise factor (ENF). Finally, each cell posses an effective dead time needed to fully recharge that cell after the photon detection. In this work the listed above unique features of SiPMs are overviewed. The reported data also contain measurements of energy resolution and 22Na time resolution.
The aim of this work is to provide the characteristics of MPPC arrays with an active area of 6 × 6 mm 2 in gamma-ray spectrometry with CsI:Tl, LSO:Ce:Ca, LaBr 3 :Ce and BGO scintillators. The chosen ...scintillators have significantly different decay times of the scintillation pulses and different wavelengths of emission peaks. This allowed an investigation into the dependence of MPPC readout features on the MPPC and scintillator characteristics. The study of influence of effective dead time and the number of MPPC pixels on a readout response in relation to the brightness and speed of the scintillator were performed. The measurements covered a selection of MPPC optimum operating voltage, verification of the linearity range for a given decay time of the crystals, verification of the excess noise factor for the optimal voltage and evaluation of the Photon Detection Efficiency (PDE). The results of energy resolution and non-proportionality obtained with the MPPC array readout of CsI:Tl and BGO were compared to those obtained for the same crystals with the XP2020Q PMT readout. The results show that an MPPC can be used as effectively as a PMT for gamma spectrometry measurements in the whole tested energy ranges (up to 1.3 MeV) and for many types of scintillation crystals (BGO, CsI:Tl).
Methods to reduce gamma-ray sensitivity of a liquid scintillator EJ309 have been studied. Zero-crossing pulse shape discrimination method was used to separate events generated by neutron and gamma ...radiation between 60−
keVee and 4
MeVee. The measurements were carried out under irradiation from an intense
137Cs source, yielding dose rate of 10
mR/h at the detector. A Pu–Be source was used to establish neutron integration window. Pile-up rejection (PUR) circuit was used to reduce gamma-ray induced events under irradiation from an intense gamma-ray source. Further, application of lead, tin and copper shields was done in order to decrease intrinsic gamma-neutron detection efficiency.
A BC523A liquid scintillator loaded with boron-10 was tested as a detector for both fast and thermal neutrons. A pulse shape discrimination (PSD) method based on a zero-crossing principle was applied ...to distinguish between neutron and gamma radiation. High quantum efficiency Photonis XP5500B photomultiplier was used to enhance light detection from the scintillator. This allowed a good registration of the energy spectrum of neutron capture events on boron-10, corresponding to about 60 keV gamma-rays. The applied PSD method proved to be useful for n/gamma discrimination. A good resolving power of the method was achieved even without gating on neutron capture events. A comparison with a standard BC501A liquid scintillator was done to evaluate thermal neutrons detection efficiency in BC523A.
Boron-10 loaded liquid scintillators were studied in order to improve n/¿ separation. Pulse shape discrimination (PSD) was implemented by means of a zero-crossing (ZC) method to distinguish between ...¿-rays and fast/slow neutrons. Significant progress was done for BC523A2 and EJ339A2 scintillators loaded with reduced amount of 10 B (2% and 2.5%, respectively), as compared to the results obtained earlier with BC523A loaded with 4.4% of 10 B. The improvement was probably caused by the reduction of 10 B content, as indicated in the reported study. A 10 B loaded scintillator EJ309B5 based on non-flammable liquid was also studied, showing the best separation of thermal neutron capture events from fast neutrons, ¿-rays and noise.
The growing interest in time-of-flight PET triggered the study of the time resolution obtainable with a 4times4times20 mm 3 LSO crystal coupled directly to the center of a 52 mm in diameter Photonis ...XP20D0 photomultiplier as well as the time resolution obtainable with the use of an 11 mm thick Lucite light diffuser that simulates the conditions in typical PET block detectors. The LSO crystal directly coupled to the PMT yielded a time resolution of 166plusmn5 ps, while in the case of light readout with the use of the light diffuser it degraded to 196plusmn5 ps and 277plusmn6 ps in the center and at the edge of the PMT, respectively. The light diffuser was coated on the sides with black tape to absorb light and to approximate in this way the realistic performance of a future block detector. Similar time resolution was obtained by coupling the LSO crystal either to the Photonis XP20D0 PMT or to a very fast 25 mm diameter Hamamatsu R5320 PMT. These results illustrate the advantages of the very low time jitter of the Hamamatsu PMT on one side, and high quantum efficiency and a screening grid at the anode of the Photonis PMT, on the other. This study strongly suggests that time-of-flight PET based on LSO crystals is a realistic proposition for the further development
We have studied the nonproportionality and intrinsic energy resolution of cerium doped YSO, GSO, LSO and LGSO crystals. While LSO and YSO have similar light output, GSO and LGSO have ca. 70% and 20% ...lower light output than LSO, respectively. YSO, a compound containing fairly light elements, was expected to have proportional light output vs. energy, like YAP:Ce. Surprisingly it has almost the same non-proportional as LSO and GSO. The nonproportionality of YSO is followed by large values of intrinsic energy resolution. The comparison of the nonproportionality of YSO-LSO and YAP-LuAP pairs indicates that high proportionality is connected with the structure of the crystal and not with the presence of light elements. To our knowledge, this is the first study of nonproportionality and intrinsic resolution for LGSO.
