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In this work we report on the performance of the MA-PMT prototype, Hamamatsu H8500C-100 MOD 8, with reduced dynode stages (eight) and super bialkali photocathode (38% Q.E. @ 380 nm). This tube represents the latest technological advancement to improve energy and spatial resolution of gamma imagers. It is particularly suitable for applications involving new high light yield scintillators. To evaluate the performances of this tube, we compared the energy and spatial resolution response with the analogous ones obtained from a standard H8500 MA-PMT coupled to a LaBr 3 :Ce scintillation crystal with the same identity. All measurements were performed with a 64 channel electronic readout. An improvement of about 10% in energy and spatial resolution was found, not properly in agreement with the increased value of quantum efficiency. However, this detector configuration permits to obtain 0.92 mm value of the intrinsic spatial resolution and 7.4% of energy resolution which represent the best results obtained with 4.0 mm thickness continuous LaBr3:Ce crystal.

The development of the molecular imaging technique based on radiopharmaceuticals is requiring sophisticated devices with sub-millimeter spatial resolution and high detection efficiency. Recently, in the field of scintillation gamma camera, it has been demonstrated that continuous crystals may improve spatial resolution with respect to the use of scintillation arrays. In this work we propose a new algorithm that improves spatial resolution. It calculates the position from a single scintillation event by squaring the charge collected on a multi-anodes photomultiplier tube (MA-PMT). It is able to remove the position linearity distortion due to the light reflections and the truncations at the crystal edge. We present measurements from a compact gamma camera based on a 51 mm × 51 mm × 4.0 mm LaBr3:Ce continuous scintillation crystal, coupled to a MA-PMT Hamamatsu H8500. The results show a strong improvement in spatial resolution and confirm the high potential in using of LaBr continuous crystal for molecular imaging applications. © 2009 Elsevier B.V. All rights reserved.

Dedicated high-resolution detectors are required for detection of small cancerous breast tumours by molecular imaging with radionuclides. Absorptive collimation is normally applied in imaging single photon emitters, but it results in a strong reduction in detection efficiency. Systems based on electronic collimation are complex and expensive. For these reasons simulations and measurements have been performed to design optimised dedicated high-resolution mini gamma camera. Critical parameters are contrast and signal-to-noise ratio (SNR). Intrinsic performance (spatial resolution, pixel identification, and response linearity and uniformity) were first optimised. Pixellated scintillator arrays (NaI(Tl)) of different pixel size were coupled to arrays of PSPMTs with different anode pad dimensions (6 6m m 2 and 3 3m m 2 ). Detectors having a field of view (FOV) of 100 100 mm 2 and 150 200 mm 2 were designed and built. The electronic system allows read out of all the anode pad signals. The collimation technique was then considered and limits of coded aperture option were studied. Preliminary results are presented.

Over the last few years our interest was dedicated to the development of small field of view imagers for Nuclear Medicine applications, particularly in Oncology. Some years ago, the authors have described an original scintillation gamma camera based on a matrix of 2 × 2 R5900-C8 Hamamatsu Position Sensitive PhotoMultiplier Tube (PSPMT) coupled to a scintillating array. The intrinsic spatial resolution obtained was adequate for high-resolution imaging applications. On the contrary, the prototype was affected by reduced performances at the borders between PSPMT. The subsequent introduction by Hamamatsu of the R7600 flange-less PSPMT family allowed to reduce the dead areas at the borders. Furthermore, Hamamatsu R7600-C12 model, improving the charge sampling with lower anode pitch, allows to improve the spatial resolution and to optimize the spatial response. Good performance was obtained with 2 × 2 R5900-C8 PSPMT array with a Combined Array-Planar Crystal (CAPC) geometry, designed by the authors. It consists of a planar crystal segmented in the top in a 15 × 15 array, 3 mm square pixel, 1mm thick, and 0.25 mm gap. Hilger manufactured two CsI assemblies, Na and Tl doped, respectively, for this study. © 2002 Elsevier Science B.V. All rights reserved.

The proposal of Mindview European Project concerns with the development of a very high resolution and high efficiency brain dedicated PET scanner simultaneously working with a Magnetic Resonance scanner, that expects to visualize neurotransmitter pathways and their disruptions in the quest to better diagnose schizophrenia. On behalf of this project, we propose a low cost PET module for the first prototype, based on monolithic crystals, suitable to be integrated with a head Radio Frequency (RF) coil. The aim of the suggested module is to achieve high performances in terms of efficiency, planar spatial resolution (expected about 1 mm) and discrimination of gamma Depth Of Interaction (DOI) in order to reduce the parallax error. Our preliminary results are very promising: a DOI resolution of about 3 mm, a spatial resolution ranging from about 1 to 1.5 mm and a good position linearity.

The introduction of Lanthanum Bromide crystal, characterized by a fast and high light emission, offers the possibility to improve both imaging spatial resolution and energy resolution in SPECT in the 80-300 kev energy range, without compromising detection efficiency. The expected performances may be limited if the crystal is used with a multi-anode PMT with Position Sensitive response due to the wide differences in the segmented anode pad gains, ranging from 2:1 to 10:1, . These characteristics may strongly deteriorate the overall energy resolution and, consequently, impair the detector imaging capability. For this reason, a 256 independent channel electronic read out was developed, based on an FPGA control, to individually read the charge on each anode. The electronics features a very low electronic noise ( < 1%) and a wide dynamic range. The readout electronics was used to build a gamma camera based on a single 100 mm × 100 mm continuous LaBr3:Ce crystal coupled to a 2 × 2 array SBA photocatode (38{%} QE) Hamamatsu H8500. An offline calibration procedure is also shown in order to compensate the anode gain variation and to exploit the LaBr3:Ce capabilities, obtaining on the whole detection area an 8.0-8.5{%} energy resolution at 140 kev. The high energy resolution performances of this gamma camera permitted to discriminate emissions from two different isotope ( Tc99m and Co57) with very close photon energy (140 and 122 kev respectively). This capability can be used to provide the gamma image with references coming from Co 57 point sources (marker) fixed at known positions. These results confirm the LaBr3:Ce crystals as one of the most interesting for all single photon emission applications. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

Many modern molecular imaging techniques, based on radiopharmaceuticals, can take advantage of sophisticated devices but are still based on the scintillation detector mechanism proposed by Anger. These devices can perform with millimeter spatial resolution and high detection efficiency, but the final performance is strongly affected by the algorithm used for the scintillation position detection. In this work, a detailed comparison of the effect on the imaging performances of three new position detection algorithms, in terms of spatial resolution, detection linearity and useful Field of View is performed on a prototype gamma detector. The detector, built by the authors, is based on a continuous LaBr3:Ce scintillation crystal coupled to an Hamamatsu MA-PMT H8500 and a single anode readout electronics. The experimental data are obtained scanning the detector surface with a Tc99m collimated source (0.4 mm φ) at 1.5 mm step. The overall imaging performances of the device are also tested by mean of a bar phantom. We conclude that the Anger-like algorithms give a 50% uFoV with a 1.30 mm ±0.05 mm spatial resolution while the proposed algorithms give a 80% uFoV and 1.10 mm ±0.06 mm spatial resolution.© 2013 IOP Publishing Ltd and Sissa Medialab srl.

In the last few years, integrated dual-imaging systems have emerged as a new modality for cancer staging with the aim to offer both functional and anatomic information. At moment the prevalent dual modality devices are based on Computer Tomography and Positron Emission Tomography. In this sense, the scientific community is debating about the high effective dose to the patient, representing an indicator of the stochastic risk, especially from Computer Tomography examination. So, a new dual modality imager, based on a Ultrasound probe and a Single Photon Emission Tomography was made in order to combine functional information, from gamma camera with structural one, obtained from the Ultrasound equipment. The Ultrasound probe is the most diffuse anatomical examination device at zero-dose, using a cost-effective and reliable method with few restriction in use. The proposed Single Photon Emission Tomography detector is a compact gamma camera (10x10 cm 2 active area), based on LaBr 3:Ce scintillation crystal coupled to 4x4 array of Hamamatsu H8500C-MOD8 Multi Anode Photomultiplier, with high spatial and energy resolution performances, equipped with rotating slant-hole collimator. A calibration phantom, made of a Co 57 point source inside a water filled box, was utilized to acquire 3D dual modality images. The detector has shown good performances in terms of spatial resolution and localization along z-axis of object of interest. This project was developed by several Italian Universities under an INFN collaboration.

In this work, we present a mean square estimation (MSE) based algorithm to calculate the position of a scintillation event within the crystal of a gamma camera dedicated to single photon imaging applications. The performances analysis takes into account pixilated and continuous shape configuration crystals, coupled to an Hamamatsu H8500C multi-anodes PMT (MA-PMT). The readout electronics used for readout has 64-independent channels each reading simultaneously the 64 anodes of the MA-PMT. An array of NaI(Tl) scintillation crystal with 2.0 mm pitch, one of CsI(Tl) with 1.6 mm pitch and one of YAP with 2.0 mm pixel size are taken into account. In addition, a continuous LaBr 3(Ce) crystal coupled to an Hamamatsu H8500C-Mod8 MA-PMT equipped with a super-bialkali photocathode (38% QE at 380 nm) was analyzed. Position linearity and spatial resolution analyzed with collimated (for continuous crystal) and uncollimated (for pixilated crystal) Co57 radioactive source and the scintillation points are calculated both with MSE and with a standard center of gravity (CoG) algorithm. The MSE algorithm improves spatial resolution and expands the useful field of view (UFOV) of the gamma camera that nearly reaches the size of the photocathode area thus showing a great advantage with respect to the CoG algorithm. © 2010 Elsevier B.V. All rights reserved.

The increasing demand of sophisticated devices for Medical Imaging, with submillimeter spatial resolution and high detection efficiency, motivates an in-depth study of detectors able to fulfill these requirements. In particular for Single Photon Emission Tomography applications, the on-going development of large LaBr3:Ce crystals makes very attractive their use as a system of gamma imaging. Single crystals can overcome the limitation in term of spatial resolution related to pixel size in scintillation arrays, once the problems of limited position linearity and image size are solved. In this work we use GEANT4 simulations in order to model different configurations based on LaBr3:Ce crystals coupled to a Hamamatsu H8500 Multi Anode Photomultiplier. The position linearity, the spatial and energy resolutions obtainable from optimum photodetection conditions are investigated. The values obtained by the Monte Carlo simulations are compared to the experimental results and found to be in good agreement with them upon tuning of some parameters.

Recently scintillators with very high light yield and photodetectors with high quantum efficiency have been opening a new way to realize gamma cameras with superior performances based on continuous crystals. Pixilated imagers have a spatial resolution limited by pixel size, in contrast with continuous scintillation crystals, where spatial resolution is a statistical function depending on light distribution spread and on generated photoelectrons from scintillation light flash. Continuous LaBr 3 :Ce crystal, with a light yield almost two times higher than NaI:Tl ones and a lower intrinsic energy resolution, could be the best candidate to carry out a gamma imaging with sub-millimeter spatial resolution and very good energy resolution. Unfortunately standard Anger algorithm produces an intrinsic position non-linearity affecting spatial resolution for small size continuous crystal. In this work we propose a new method to calculate the position mean value by squaring the 2D collected charge distribution on a multi-anodes photomultiplier tube (MA-PMT). In this study we take into account four different detector configurations: three sample of LaBr 3 :Ce scintillation crystals, 49mm×49mm area, a couple of 4.0 with different surface treatment and a single 10 mm thick, with 3 mm glass window. Moreover a forth one with 5.0mm thickness which was integral assembled with an Hamamatsu H8500. We applied the new position algorithm to simulated data, obtained by Geant4 code and afterwards to the experimental data obtained scanning the different detectors with 0.4 mm O collimated Tc99m point source, at 1.5 mm step. The results obtained with the new algorithm show an improvement in position linearity and in spatial resolution of about a factor two. The best values in terms of spatial resolution were 0.9 mm, 1.1 mm and 1.8 mm for integral assembled, 4.0 mm thick and 10 mm thick LaBr 3 :Ce crystal respectively. These results demonstrate the potential of LaBr crystal for molecular imaging application and more in general for gamma ray imaging

Nuclear medicine imaging devices commonly use multi-element photo detection systems, composed of an array of N × N elements, each one providing an individual signal. Many strategies have been developed to reduce the number of readout channels, one of the main approaches is the Rows and Columns (R/C) projection logic. In this paper we proposed a modified version of Raised To the Power (RTP) algorithm adapted to R/C logic. In order to validate its efficiency a linear scanning irradiation on two 49× 49 mm2 LaBr3:Ce (0.5%) crystals with different thickness (4 mm and 10 mm) was carried out. Imaging performance analysis was made in terms of position linearity, Field-of-View (FoV) enlargement and spatial resolution. Imaging results from Anger Logic, RTP algorithm based on single element readout and RTP algorithm based on R/C readout were compared. A notable advantage of using RTP algorithms instead of Anger Logic was found: the FoV widens from about 30% to more than 70% of the detector area whereas the spatial resolution is highly improved, especially for off-center interactions, both for 4 mm-thick and 10 mm-thick crystals. Furthermore, imaging performance with the R/C readout is just slightly different from the single element one (FoV reduction less than 7% and SR worsening less than 10%). The R/C adapted RTP algorithm opens doors to high imaging performance with a substantial reduction of complexity and cost in the readout electronics.

The aim of this paper is to investigate the intrinsic spatial resolution limit by coupling a CsI(Tl) micro-pixel scintillation array to position sensitive photomultipliers (PSPMTs) for ultra-high resolution gamma-ray imaging. On this purpose, 1 mm thick array with 0.2 mm pixel side, 0.4 mm pitch has been realized by Spectra Physics (Hilger). The present scintillation arrays technology is suitable to produce larger crystal areas. In this paper we present spatial resolution and positioning results obtained by coupling the micro-pixel scintillation array to Hamamatsu square PSPMTs: 1rdquo R8520-C12, 1rdquo R5900-L16 and 2rdquo H8500 Flat panel PMT. Preliminary measurements demonstrate better performance in term of uniformity response when micro-pixel array is coupled to a H8500 PSPMT model. This setup carries out an intrinsic spatial resolution lower limit of about 0.6 mm FWHM at 50% FWHM energy resolution, defining it as the minimum scintillation array pitch detectable at 122 keV. The results obtained by R5900-L16 with a better sampling of the scintillation light has shown an improvement of the position linearity in spite of a worse spatial resolution due to the poor light output of scintillation array.

High spatial resolution, small Field Of View (FOV), fully portable scintillation cameras are lower cost and obviously lower weight than large FOV, not transportable Anger gamma cameras. Portable cameras allow easy transfer of the detector, thus of radioisotope imaging, where the bioptical procedure takes place. In this paper we describe a preliminary experience on radionuclide Breast Cancer (BC) imaging with a 22.8 × 22.8 mm2 FOV minicamera, already used by our group for sentinel node detection with the name of Imaging Probe (IP). In this work IP BC detection was performed with the aim of guiding biopsy, in particular open biopsy, or to help or modify fine needle or needle addressing when main driving method was echography or digital radiography. The IP prototype weight was about 1kg. This small scintillation camera is based on the compact Position Sensitive Photomultiplier Tube Hamamatsu R7600-00-C8, coupled to a CsI(Tl) scintillation array 2.6 × 2.6 × 5.0 mm3 crystal-pixel size. Spatial resolution of the IP was 2.5 mm Full-Width at Half-Maximum at laboratory tests. IP was provided with acquisition software allowing quick change of pixels number on the computer acquisition frame and an on-line image-smoothing program. Both these programs were developed in order to allow nuclear physicians to quickly get target source when the patient was anesthetized in the operator room, with sterile conditions. 99mTc Sestamibi (MIBI) was injected at the dose of 740 MBq 1 h before imaging and biopsy to 14 patients with suspicious or known BC. Scintigraphic images were acquired before and after biopsy in each patient. Operator was allowed to take into account scintigraphic images as well as previously performed X-ray mammograms and echographies. High-resolution IP images were able to guide biopsy toward cancer or washout zones of the cancer, that are thought to be chemoresistant in 7 patients out of 10. Four patients, in whom IP and MIBI were not able to guide biopsy, did not show cancer. Two patients in whom biopsy was performed in the high washout zone, did show Multi Drug Resistance (MDR) gene product at immunohistochemistry on bioptical samples. Specific radioactivity was measured on biopsy specimens and measurement confirmed the etherogeneous distribution of MIBI within cancers. Our study confirms the ability of IP to guide breast biopsy even when our mini-camera has to be manually handled by trained physicians during operation. © 2002 Elsevier Science B.V. All rights reserved.

Recently the application of small imagers in nuclear medicine is growing, particularly in scintimammography. In this paper we propose the use of the Hamamatsu R7600-C8 Position Sensitive Photomultiplier Tube (PSPMT) for detection image optimization in scintimammography through the evaluation of image performances of detector pixellation and its interaction with a collimator lattice . To this aim, a number of CsI(Tl) scintillating arrays with different pixel size and thickness were coupled to the same PSPMT. Considering the very high intrinsic spatial resolution, a look up table was realized to correct accurately the gain non uniformities. The results show an overall energy resolution FWHM, from flood field irradiation source, in close agreement with the individual crystal response and an uniformity response within ± 10%. Finally an analysis of tumor signal to noise ratio (SNR) as a function of detection pixellation was performed, utilizing a breast phantom. Tumor SNR values are highest for 5 mm thick CsI(Tl) arrays but shown slight differences with pixel size. The best tumor SNR value for 6 cm breast thick was obtained with 1.5 × 1.5 mm2 crystal pixel size. The collimator used was a low energy all purpose, parallel hole collimator with 22 mm length, 1.5 mm hexagonal hole, 0.2 mm Pb septa, currently utilized in scintimammography.