Si-APD readout for LaBr3 : Ce scintillator

In this work, we report and compare the results of gamma-ray spectroscopy measurements performed using a LaBr3:Ce crystal coupled to a photornultiplier tube with modified base and to a Si-avalanche photodiode readout by standard electronics. Energy resolution values have been obtained in the range from 59.5 keV (Am-241) to 1332 keV (Co-60). Good linearity in energy response has been found. Energy resolution values obtained with avalanche photodiode readout are underestimated due to the small active area of the presently available photosensor with respect to crystal dimension. (c) 2006 Elsevier B.V. All rights reserved

Spectrometric performances of high quantum efficiency multi and single anode PMTs coupled to LaBr3(Ce) crystal

High quantum efficiency semiconductor photodetectors have recently drawn the attention of the scientific community for their potential in the realization of a new class of scintillation imagers with very high energy and spatial resolution performance. However, this goal does not seem within easy reach, due to various technological issues such as, for example, the difficulty to scale the characteristics of a single detector to an imager with suitable dimensions. Lately a definite technical improvement in increasing quantum efficiency up to 42% for position sensitive photomultipliers was achieved. The aim of this work is thus to test this new technological progress and to study the possible implications in imaging applications. Four Hamamatsu PMTs were tested: two multi anode photomultipliers, one with a bialkali (27% quantum efficiency) and the other one with a super-bialkali photocathode (38% quantum efficiency), and two 1 x 1 in. PMTs, both equipped with an ultra bialkali photocathode (42% quantum efficiency). In particular one of the ultra bialkali PMT has also an increased efficiency of first dynode charge collection. The results were compared with the ones obtained with a reference PMT (Hamamatsu R6231), mainly used in spectroscopy. The PMTs were coupled to LaBr3(Ce), NaI(Tl) and LSO(Ce) continuous scintillation crystals. The tests were done using two independent electronic chains: one dedicated for spectroscopic application and a second one, using a multi wire 64 channel readout, for imaging applications. The super-bialkali MA-PMTs have shown high energy resolution, both with spectroscopic and imaging setup, highlighting the appropriateness of these devices for the development of imaging devices with high spectroscopic performance. (C) 2013 Elsevier B.V. All rights reserved

Spectral matching factors for LaBr3:Ce crystals coupled to Hamamatsu H8500 family PMTs

The matching between the spectral distribution of the scintillation light from a LaBr3:Ce crystal and the spectral distribution of the quantum efficiency of a Photomultiplier Tube (PMT) can be characterized by a matching factor whose value depicts, in the range from 0 to 1, the efficiency of PMT for the crystal. A systematic survey of literature was carried out identifying a set of 44 LaBr3:Ce emission spectra and 11 spectral quantum efficiencies of PMTs, all published in the years 20022010. Results showing the values of matching factors calculated for all the spectral combinations are presented and commented upon. © 2011 Elsevier B.V. All rights reserved

Reliability of high quantum efficiency MA-PMT for spectrometric quality assurance of scintillation imagers

The outstanding semiconductor photodetectors with high quantum efficiency have interested the scientific community for their potential of assembling a new class of scintillation imagers with very high energy and spatial resolution performances at low cost. Recently we assisted also to a strong technological advance in Photo Multiplier Tube (PMT) by increasing of photocathode Quantum Efficiency (QE) up to 42% peak value. From a pragmatic point of view the aim of this work is to test if this technology is ready for imaging applications and mainly focused on the investigation of energy resolution and pulse height linearity performances. Two Multi Anode PMTs (MA-PMT) were tested: a standard Hamamatsu 88500 and a new modified one, equipped with SuperBiAlkali (SBA) photocathode, with enhanced QE. The PMTs were coupled to a LaBr3(Ce) continuous crystal dedicated for imaging application. The MA-PMT responses were tested utilizing two electronic chains: one dedicated for spectroscopy, where the 64 PMT outputs were reduced to only one signal, and a second one, utilizing 64 channels readout for imaging. These MA-PMTs have shown very good linearity response, up to 1 MeV photon energy, and high performances in term of energy resolution, demonstrating that this technology is particularly indicated to develop imaging devices with enhanced spectroscopic response

Monte carlo simulation to evaluate factors affecting imaging performances of compact scintillation gamma camer

In recent years, a new generation of compact gamma cameras, based on monolithic scintillation crystals, has become increasingly widespread. The main advantages of small FoV gamma cameras with respect to the standard ones are high portability, low cost and low weight, allowing several clinical applications, from scintimammography to intraoperative tumor localization. In gamma cameras based on continuous scintillation crystals, intrinsic Spatial Resolution (SR) is mainly affected by two factors: scintillation light collection efficiency and overall crystal thickness. The first affects the counting statistics, the latter impacts on the light distribution width. To fully investigate the potentiality of these devices we took advantage of Monte Carlo simulations as a valuable tool to physically characterize the imaging systems and to establish a priori reference values. GEANT4 toolkit allows to completely describe the phenomenon of light emission and propagation through the media, providing control to all second-order factors existing in real systems. Results show clearly that SR is dependent on the number of photoelectrons produced and on the light spread. Furthermore, the role of refractive index has been unambiguously identified as an important factor affecting light collection and consequently SR

New position arithmetic for scintillation camera based on floating weight system

Over the last thirty years we have been seeing impressive advances in photodetection technology and in scintillation crystal production and manufacturing. Researchers proposed an impressive variety of small FoV scintillation cameras or detector modules for SPET and PET. The original position arithmetic based on linear weight is still widely used although this logic generates a conflict between position linearity and spatial resolution. In this paper, we propose a method of position arithmetic based on floating weights, simply utilizing non linear amplification of anode charge. The method has been tested on a continuous LaBr3:Ce scintillation crystal 51x51 mm(2) area and 4.0 mm thickness coupled to a Hamamatsu H8500 multi-anodes PMT. The charge collected on each anode was independently digitized, so to be free to apply to the charge distribution any different non linear transformation. In this way the charge around the peak is much more weighed then the remaining. As a result, we obtain a floating weighting matrix according to event interaction location. Comparing the data with the analogous ones from linear weights, it resulted a general improvement of more than 30% of position calibration slope and of spatial resolution values. Position linearity response and spatial resolution values resulted in good agreement with simulated ones. The best spatial resolution value was about 1.0 mm and position linearity resulted in close agreement with that of scintillation array

Detection of sentinel node in breast cancer: Pilot study with the imaging probe

The commonly used gamma probes are easy to use but also give rough information when employed in radioisotope-guided surgery. When images are required for exact localization, a gamma camera as well as a probe have to be used. Position-sensitive photomultipliers have contemporaneously allowed high-resolution scintigraphy and miniaturization of gamma cameras. We have assembled a miniature gamma camera with a 1-square-inch field of view and an intrinsic resolution of about 1 mm. When the minicamera is collimated with a large-holed, highly sensitive collimator, it acquires a spatial resolution of 3 mm. This prototype has been tested in the detection of difficult-to-image breast cancer sentinel nodes. Five nodes that had not been found with the usual technique of an Anger camera plus conventional probe were checked with the miniature camera that we named imaging probe: it actually is small enough to be used as a probe and large enough to give an image. One of the five nodes was found and imaged. It was small, disease-free, close to the tumor and probably hidden by the Compton halo around the peritumoral injection site. Our pilot study shows that the imaging probe, although still a prototype, has certain advantages over conventional methods when lymph node localization is required during surgery

Multi-printed inkjet phantoms for radionuclide molecular imaging

This work describes the multi-printing technique for preparing, with a commercial inkjet printer and radio marked ink, planar emission phantoms particularly suitable for high-resolution radionuclide imaging. The well known practice of producing radioactive phantoms by inkjet was improved by developing the multi-printing technique definable as the reiteration of printing commands before processing the next line. The major advantage consists of the increase of the concentration of radioactivity deposited in the image with respect to the standard over-printing method without refilling radioactivity in the cartridge. Since the paper needs just one insertion in the printer, a better outlined image is produced than in the case of the over-printing technique obtainable by reiterating both the insertion and the printing of the same image over of the same sheet. This paper discusses in particular: (1) the linear dependence of deposited activity vs. the number of multi-printing cycles; (2) the effective decay’s time of radio marker at nozzle’s output; (3) the evaluation of the absolute value of the activity deposited in the image and (4) the broadening of the printed surfaces vs. the number of multi-printing cycles

Continuous DoI determination by gaussian modelling of linear and non-linear scintillation light distributions

The Depth of Interaction (Dol) detection is crucial in many medical imaging applications such as small ring PET and high resolution SPECT. In this work we investigate the possibility to discriminate the Dol using continuous crystals. A LaBr3(Ce) crystal has been used in the detection system for its intrinsic high light yield, that especially at low energies (e. g. 140 keY) reduces considerably the statistical uncertainties increasing the Dol discrimination power. The innovative suggestion of this work is the use of spectrometric observables to discriminate events on top and bottom of the crystal, under the hypothesis that scintillation light distributions can be parameterized by a gaussian model. The spread of the light cone (sigma) is proportional to the Dol simply by geometrical considerations, but under the gaussian hypothesis relations between the spectrometric variables (maximum high I and integral of the distribution N) and the Dol become a straightforward consequence. Two methods are proposed and discussed: a linear treatment of the light distribution and a non linear (quadratic) manipulation of it. The expected correlations between the spectrometric variables (N and I), according to the gaussian model, are checked using a specific Monte Carlo simulation of the experimental apparatus. Those are then compared with experimental data obtained irradiating the LaBr3:Ce crystal with a Tc-99m collimated source. A close agreement between experimental data and MC is verified. Finally, a preliminary test on experimental data has been performed irradiating the crystal with a Co-57 source, in order to investigate the strong dependence of the non linear manipulation of the light distribution to the DoI

Multi-printed inkjet phantoms for radionuclide molecular imaging

This work describes the multi-printing technique for preparing, with a commercial inkjet printer and radio marked ink, planar emission phantoms particularly suitable for high-resolution radionuclide imaging. The well known practice of producing radioactive phantoms by inkjet was improved by developing the multi-printing technique definable as the reiteration of printing commands before processing the next line. The major advantage consists of the increase of the concentration of radioactivity deposited in the image with respect to the standard over-printing method without refilling radioactivity in the cartridge. Since the paper needs just one insertion in the printer, a better outlined image is produced than in the case of the over-printing technique obtainable by reiterating both the insertion and the printing of the same image over of the same sheet. This paper discusses in particular: (1) the linear dependence of deposited activity vs. the number of multi-printing cycles; (2) the effective decay’s time of radio marker at nozzle’s output; (3) the evaluation of the absolute value of the activity deposited in the image and (4) the broadening of the printed surfaces vs. the number of multi-printing cycles