Search

In this work, an experimental comparison of the capabilities of a scintillation detector based on a NaI:Tl and a LaBr 3 :Ce monolithic crystals is presented. The main advantage of LaBr 3 :Ce respect to NaI:Tl is its very high light yield (i.e. 63photons/keV versus 38photons/keV), allowing a considerable improvement of the statistical factor affecting light collection and, consequently, Spatial Resolution (SR) and Energy Resolution (ER). Nevertheless, the following results show that the improvement of the SR with the LaBr 3 :Ce is smaller than expected. As analyzed, it could be due to the LaBr 3 :Ce refractive index higher than the NaI:Tl one, that leads to a loss of scintillation light. In fact, the measurements produce similar imaging results (SR at crystal center is about 1.1mm for both crystals), while the ER is slightly better for the LaBr 3 :Ce, as expected (7.6% and 8.8% for LaBr 3 :Ce and NaI:Tl, respectively). This work encourages a further and more specific analysis about how the refractive index affects the amount and the shape of crystal light distribution.

Recently, dual-modality systems have been developed, aimed to correlate anatomical and functional information, improving disease localization and helping oncological or surgical treatments. Moreover, due to the growing interest in handheld detectors for preclinical trials or small animal imaging, in this work a new dual modality integrated device, based on a Ultrasounds probe and a small Field of View Single Photon Emission gamma camera, is proposed. © 2018 Elsevier Ltd

Nuclear Medicine SPECT imaging is taking on new challenges, regarding the improvement of quality and contrast of images. In order to reach this goal, energy resolution and Compton rejection capability have to be enhanced. For detectors based on scintillation crystal, the choice of a scintillator with high light yield is suitable; recently one of the major candidates is Lanthanum Tri-Bromide (LaBr3:Ce), with its high 63,000 ph/MeV light yield. Unfortunately, LaBr3:Ce suffers size limitations due to the actual growth techniques (maximum 3 in. diameter) and has also elevated cost. For these reasons, great interest is shown on small field of view detectors based on LaBr3:Ce, thought for imaging of specific physiological process or organ. To improve energy resolution, continuous crystals are more appropriate instead than pixelated ones. Since in a continuous crystal a decrease in position linearity, due to the light reflections, is typically obtained at the edges, an absorbent treatment of surfaces is generally utilized for SPECT applications. On the other hand, light absorption causes a relevant degradation of local energy resolution and pulse height uniformity response, affecting local image contrast. In this work an analysis on a new continuous LaBr3:Ce scintillation crystal with size proper to a small field of view gamma imager but with reflective treatment of surfaces is presented. This leads up to outstanding overall and local energy resolution results and excellent pulse height uniformity response on the whole field of view. Furthermore, preliminary imaging results are satisfactory, compared to the ones from a scintillation crystal with absorbent edges.

We present an imaging characterization of a 10 x 10 LuYAP array (2 x 2 x 10 mm3 pixels) with an innovative dielectric coating insulation (0.015 mm thick), in view of its possible use in a gamma camera for imaging positron emission tomography (PET) or in similar applications, e.g. as γ-prompt detector in hadron therapy. The particular assembly of this array was realized in order to obtain a packing fraction of 98%, improving detection efficiency and light collection. For imaging purpose, the array has been coupled with a selected Hamamatsu H10966-100 Multi Anode Photomultiplier read out by a customized 64 independent channels electronics. This tube presents a superbialkali photocathode with 38% of quantum efficiency, permitting to enhance energy resolution and consequently image quality. A pixel identification of about 0.5 mm at 662 keV was obtained, highlighting the potentiality of this detector in PET applications. © 2017 IOP Publishing Ltd and Sissa Medialab srl.

The ECORAD collaboration aims at developing a dual compact camera for acquiring ultrasound and scintigraphic images, in order to get both morphological and functional information on the same device. A final volumetric image containing the fusion information will be provided to the user. Here we present the first simulated results of the scintigraphic camera, achieved by means of the GEANT4 program. The camera is based on a four-segment slant collimator. Each segment is coupled with a planar LaBr3(Ce) scintillator and to a Position Sensitive Photo-Multiplier Tube. We tested two different centroid algorithms for reconstructing the planar images. The 3D information is recovered from the planar images acquired at each position of the rotating collimator by using a simple back-projection algorithm. The proposed approach of a scintigraphic camera based on slant collimators is able to recover the location and the depth of a lesion in a very accurate way.

The performance of the new prototype of high quantum efficiency PMT (43% at 380 nm), Hamamatsu R7600U-200, was studied coupled to a LaBr 3 :Ce crystal with the size of ∅12.5 mm×12.5 mm. The energy resolution results were compared with ones from two PMTs, Hamamatsu R7600U and R6231MOD, with 22% and 30% quantum efficiency (QE), respectively. Moreover, the photodetectors were equipped with tapered and un-tapered voltage dividers to study the non-linearity effects on pulse height distribution, due to very high peak currents induced in the PMT by the fast and intense light pulse of LaBr 3 :Ce. The results show an energy resolution improvement with UBA PMT of about 20%, in the energy range of 80–662 keV, with respect to the BA one.

Purpose Nuclear medicine imaging based on commonly used gamma cameras, which are large, bulky and designed for general-purpose imaging, is limited in detecting small lesions often indicative of early stage diseases. To overcome this limitation, the authors propose a gamma tomosynthesis method based on variable tilt-angle collimation system that, complemented by a conventional gamma camera, is able to perform high-resolution three-dimensional imaging. Methods The variable tilt-angle collimator allows to acquire a set of planar images at different angles, which are then 3D reconstructed through the Shift And Add (SAA) method [1] . Spatial resolutions were measured in reconstructed images using a point source at different source-to-collimator distances; sensitivity was evaluated over the range of slant angles (from −45°to 45°) using a disk source. Image contrast (IC) and contrast to noise ratio (CNR) of sub-centimeters tumours were evaluated using a breast phantom. Furthermore, the capability of the tomosynthesis technique in preserving axial resolution was tested by using the Mini Defrise phantom. Gamma tomosynthesis images were compared with those obtained with a standard circular-orbit SPECT scan. Results The proposed system allows reaching spatial resolutions in the x-y plane ranging from 9 to 14 mm over a depth range of 6-10 cm; spatial resolution in the depth dimension becomes two times greater than those in the other two dimensions. The measured sensitivity decreased from 9 cps/ μ Ci to 6 cps/ μ Ci varying the slant angle from 5° to 45degr . The IC and CNR resulted from gamma tomosynthesis images demonstrated a significant improvement compared to SPECT. Conclusions The proposed gamma tomosynthesis demonstrated the potential for superior lesion detection in nuclear medicine imaging. Differently from the currently used SPECT, a conventional gamma camera equipped with the variable tilt-angle collimator could be located at the minimum distance from the patient, thus improving detection, localisation and characterisation of sub-centimetre lesions.

The Depth of Interaction (DoI) discrimination of gamma-photons within scintillation crystals allows to improve imaging performance in PET scanners as well as in SPECT devices equipped with non-parallel collimators (e. g. pinhole ones). In previous works, the authors experimentally proved the efficiency of a DoI-encoding technique in case of a 20 mm-thick monolithic crystal PET module. For the thinner crystals commonly used in SPECT, DoI determination still remains a challenging goal. To this aim, in this work the authors have experimentally evaluated the DoI-encoding method on a 6 mm-thick monolithic LaBr3:Ce crystal. The results prove the efficiency and reliability of the proposed method. It indeed allows to discriminate the gamma photons interacting at the the top and the bottom of the crystal.

Phoswich detectors based on scintillation crystals are widely diffused for both PET and SPECT applications. In order to separate the signals arising from different layers many methods have been proposed in literature. Separation of the layers commonly relies on time discrimination or pulse height discrimination. In this work, by means of experimental measurement on a phoswich detector based on Lanthanum Bromide and Lutetium Fine Silicate monolithic crystals, a novel method allowing to separate signals coming from different layers has been evaluated. The main feature of this method, specifically developed for phoswich based on monolithic scintillation crystals, is the discrimination capability based on the scintillation light distribution shape. For this reason, the findings that will be shown could be easily extended to whatever combination of scintillator, independently from their decay time or light yield.

During the last years the research for new scintillation crystals has been crucial for the improvement of imaging performance in nuclear medicine applications. Crytur company has recently released two new scintillators named CRY-018 and CRY-019 which are non hygroscopic, have short decay time and low refraction index. They represent the ideal candidates to substitute NaI:Tl and BGO crystals in future PET ad SPECT applications. The purpose of this work is to characterize this unknown crystals, look for possible applications in imaging for nuclear medicine. The results of this work were compared with the results obtained with a LaBr3:ce scintillation crystal. This particular crystal is used as a comparison benchmark because of its strong linear pulse height uniformity response and high energy resolution. Measurements have been performed with a high count rate which is typical for medical applications. Irradiation of the crystals have been performed in three different geometries and in a photon energy range suitable with SPECT and PET applications. The experimental results identify the CRY-018 as an Yttrium and Silicon mixture and the CRY-019 with as Lutetium and Silicon one. Moreover a light yield of about 45% of LaBr3 one, was obtained for both the CRY-018 and CRY-019. This is one of the higher light yield between most of the scintillation crystals usually used in nuclear medicine. Both crystals are characterized by a non-proportionality in the pulse height linearity response. Energy resolutions of 7.4% for CRY-018 and 8.4% for CRY-019 at 661 keV, have been measured. The intrinsic component of the energy resolution has been esteemed for all three scintillators. An intrinsic detection efficiency of about 45% at 122 keV for CRY-018 and 14% at 661 keV for CRY-019 has been measured. Compared with LaBr3:Ce efficiency, which is highly deteriorated by the coating required by the hygroscopicity, CRY-018 and CRY-019 are really interesting considering that these two samples are only 6 mm thick. Crytur's crystals seem to be suitable for nuclear medicine applications.

Spatial localization of radioactive sources is currently a main issue interesting different fields, including nuclear industry, homeland security as well as medical imaging. It is currently achieved using different systems, but the development of technologies for detecting and characterizing radiation is becoming important especially in medical imaging. In this latter field, radiation detection probes have long been used to guide surgery, thanks to their ability to localize and quantify radiopharmaceutical uptake even deep in tissue. Radiolabelled colloid is injected into, or near to, the tumor and the surgeon uses a hand-held radiation detector, the gamma probe, to identify lymph nodes with radiopharmaceutical uptkake. The present work refers to a novel scintigraphic goniometric probe to identify gamma radiation and its direction. The probe incorporates several scintillation crystals joined together in a particular configuration to provide data related to the position of a gamma source. The main technical characteristics of the gamma locator prototype, i.e. sensitivity, spatial resolution and detection efficiency, are investigated. Moreover, the development of a specific procedure applied to the images permits to retrieve the source position with high precision with respect to the currently used gamma probes. The presented device shows a high sensitivity and efficiency to identify gamma radiation taking a short time (from 30 to 60 s). Even though it was designed for applications in radio-guided surgery, it could be used for other purposes, as for example homeland security.

The aim of the ECORAD collaboration is to develop a dual integrated compact and portable camera able to acquire ultrasound and scintigraphic images at the same time. In this work, we present some simulated results of the scintigraphic part of the system. This camera consists of a rotating slant collimator with four segments connected to a planar LaBr3:Ce scintillator and to a PMT Hamamatsu Flat Panel H8500. Simulations are achieved by means of the GEANT4 program. The volumetric information is reconstructed from the planar images acquired at each position of the rotating collimator by means of a simple back-projection method. Results showed that the planar spatial resolution is better that the axial one. First preliminary results suggest that the detection limit of the camera is about 15:1 (in terms of Tumor/Background ratio) for a spherical tumor with 8 mm diameter located at 3 cm distance from the collimator. This confirms that with our approach it is feasible to develop a compact camera able to recover the 3D position of lesions located at small depths (up to some centimeters), without the need of rotating the camera around the body.

The authors report on the performance of two small field of view, compact gamma cameras working in single photon counting in planar imaging tests at 122 and 140 keV. The first camera is based on a LaBr 3 : Ce scintillator continuous crystal ( 49 × 49 × 5 mm 3 ) assembled with a flat panel multianode photomultiplier tube with parallel readout. The second one belongs to the class of semiconductor hybrid pixel detectors, specifically, a CdTe pixel detector ( 14 × 14 × 1 mm 3 ) with 256 × 256 square pixels and a pitch of 55 μ m , read out by a CMOS single photon counting integrated circuit of the Medipix2 series. The scintillation camera was operated with selectable energy window while the CdTecamera was operated with a single low-energy detection threshold of about 20 keV, i.e., without energy discrimination. The detectors were coupled to pinhole or parallel-hole high-resolution collimators. The evaluation of their overall performance in basic imaging tasks is presented through measurements of their detection efficiency, intrinsic spatial resolution, noise, image SNR, and contrast recovery. The scintillation and CdTecameras showed, respectively, detection efficiencies at 122 keV of 83% and 45%, intrinsic spatial resolutions of 0.9 mm and 75 μ m , and total background noises of 40.5 and 1.6 cps. Imaging tests with high-resolution parallel-hole and pinhole collimators are also reported.

The Hamamatsu H8500 Flat Panel PMT is the latest technological advancement in gamma ray imaging. Its compact size makes it attractive for medical imaging applications. To study and compare image performance a Flat Panel PMT, representing the present production, was coupled to CsI(Tl) and Nal(Tl) scintillation arrays with 3 mm and 1.8 mm pixel size respectively and connected to a multi-anode electronic readout. Furthermore, a pulsed blue LED coupled to an optical liber was utilized to scan the tube with different light distributions. This study investigated how PMT anode gain uniformity response, scintillation light distribution and intensity influence the spatial resolution, the position linearity and the image noise. Each crystal in the scintillation array produces a different charge distribution, which depends on the match between the anode size and the scintillation array lattice. The Nal(Tl) array demonstrated to fit both PMT characteristics and dynamic range of electronic read out, due to the charge distribution adequate to the anode size. For CsI(Tl) crystal, the pulse height calibration resulted more critical, due to the narrow light distribution. In conclusion, the use of Flat Panel tube with selected anode gain uniformity could represent the cheapest and easiest solution to obtain the best image quality, in particular for scintillator array with smaller pixel size.

Dedicated high resolution detectors are needed for detection of small tumors by molecular imaging with radionuclides. Absorptive collimation are typically used for imaging single photon emitters, but it results in a strong reduction in efficiency. Systems based on electronic collimation offer higher efficiency but they are complex and expensive. In case of scintimammography, dual-head detectors increase sensitivity and cancel out the dependence of the lesion depth. In the system presented here, pixellated scintillator arrays (NaI:Tl) were coupled to arrays of PSPMT's, HPK H8500 Flat Panel. A dual-head detector having field of view of 100×100 mm2 and 150×200 mm2 were designed and built. The electronic system allows readout of all the anode pad signals. First clinical trials, performed in the framework of the Scintimammography project of Italian National Institute of Health and University of Tor Vergata in Rome, and University of Naples, are presented.

The imaging capabilities of radioisotope molecular imaging systems are limited by their ring geometry and by the object-to-detector distance, which impairs spatial resolution, efficiency and image quality. These detection capabilities could be enhanced by performing acquisitions with dedicated gamma cameras placed in close proximity to the object that has to be examined. The main aim of this work is to develop a compact camera suitable for detecting small and low-contrast lesions, with a higher detection efficiency than conventional SPECT, through a gamma emission tomosynthesis method. In this contribution a prototype of a new automated slant hole collimator, coupled to a small Field of View (FoV) gamma camera, is presented. The proposed device is able to acquire planar projection images at different angles without rotating around the patient body; these projection images are then three-dimensional reconstructed. Therefore, in order to perform the volumetric reconstruction of the studied object, the traditional Back Projection (BP) reconstruction is compared with the Shift And Add (SAA) method. In order to verify the effectiveness of the technique and to test the image reconstruction algorithms, a Monte Carlo simulation, based on the GEANT4 code, was implemented. The method was also validated by a set of experimental measurements. The discussed device is designed to work in patient proximity for detecting lesions placed at a distances ranged from 0 to 8 cm, thus allowing few millimeters planar resolutions and sagittal resolution of about 2 cm. The new collimation method implies high-resolution capabilities demonstrated by reconstructing the projection images through the BP and the SAA methods. The latter is simpler than BP and produces comparable spatial resolutions with respect to the traditional tomographic method, while preserving the image counts. © 2015 IOP Publishing Ltd and Sissa Medialab srl.

The simultaneous administration of radiopharmaceuticals labeled with more than one radioisotope is becoming of increasing interest in clinical practice. Because the photon energies of the utilized radioisotopes could be very close (less than 15% difference), a gamma camera with adequate energy resolution is required. The availability of scintillation crystals with high light yield, as lanthanum tri-bromide (LaBr3:Ce), is particularly appealing for these applications. In this work, a new small field of view gamma camera prototype is presented, based on a planar LaBr3:Ce scintillation crystal with surfaces treatment typical of spectrometric devices, in order to enhance energy resolution performances. The crystal has round shape and has been optically coupled with a position sensitive photomultiplier tube with high quantum efficiency. The presented gamma camera shows outstanding energy resolution results in the investigated energy range (32–662 keV). These relevant performances have been obtained through the application of uniformity correction on the raw data, necessary due to the presence of position sensitive phototube, characterized by a spread of anodic gain values. In spite of position linearity degradation at crystal edges, due to reflective treatment of surfaces, intrinsic spatial resolution values are satisfactory on the useful field of view.The characterization of the presented gamma camera, based on a continuous LaBr3:Ce scintillation crystal with reflective surfaces, indicates good performances in multi-isotope imaging due to the excellent energy resolution results, also in comparison with similar detectors.

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.

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.

In vivo imaging of pharmaceuticals labeled with radionuclides has proven to be a powerful tool in human subjects. The same imaging methods have often been applied to small animal but usually only within the nuclear medicine (NM) community, and usually only to evaluate the efficacy of new radiopharmaceuticals. We have built a compact mini gamma camera, a pixellated array of NaI(Tl) crystals coupled to 3′′ R2486 Hamamatsu Position Sensitive PMT; in combination with a pinhole collimator, which allows for high resolution in vivo SPECT imaging. Calculations show that reasonable counting rates are possible. The system has been tested and preliminary measurements on mice have been done. The performances of the camera are in the expectations. Improvements will be done both on the collimation technique and on the detector. Simulations have been performed to study a coded aperture collimator. The results show that the efficiency can be greatly improved without sacrificing the spatial resolution. A dedicated mask has been designed and will be used soon.

An analytical and a statistical approach to describe the scintillation crystal arrays responses are presented in order to identify crystal detectors. They were applied to two flood-field irradiation images, with and without strong distortion and no linearity. The comparison of the outcomes suggests that the first and simplest to apply one is appropriate for light distortion, whereas the second and more complex statistical approach is unavoidable in the presence of strong distortions of the image.

A Monte Carlo simulation of a 50 mm × 50 mm × 4 mm continuous crystal has been developed to investigate the correlation between the scintillation light width (σ) and the Depth of Interaction (DoI) within the crystal. Our studies are based on a LaBr3(Ce) crystal, in order to take advantage of its high light yield to reduce the statistic uncertainties on the estimators of the σ. The first one, the standard deviation of the light distribution, has demonstrated a poor, though linear, correlation to DoI, that is not experimentally detectable. Otherwise, the second estimator, N I , is the ratio of the total number of photoelectrons to the maximum number of photoelectrons collected from a single anode, in a scintillation event. N I has been found to have the best correlation to DoI, that provides 2 mm resolution.

In this paper the response in term of pulse height linearity of two Hamamatsu photomultipliers is investigated, when coupled to a LaBr 3 :Ce scintillation crystal. The two photodetectors have high quantum efficiency and in particular 30% for R6231-01 and 42% for R7600-200 tube. The substantial difference is in the dynode structure, linear focused and metal channel for R6231 and R7600 respectively. In this work in order to verify the non-linearity effects on the pulse height distribution, due principally to the high and fast light production of LaBr 3 :Ce scintillator, we propose a ‘peak by peak’ procedure to calibrate the pulse height distribution. Utilizing a specific fragmentation of the calibration curve in subsets, the calculated energy values are very similar for both PMTs. This result confirmed the potentiality of the procedure to highlight the non-linearity effects on pulse height distribution.

Over the last years Nuclear Medicine and Oncology require the development of new scintigraphic imagers dedicated to particular organs and lesions, with improved performances with respect to presently available devices. In order to enhance the imaging responses, pixellated crystals have to be employed as scintillating devices coupled to position sensitive photomultiplier tubes. Some of major steps forward in this field could be obtained by using the recently produced Hamamatsu photomultiplier tubes. The knowledge of the pixel scintillation light distribution at photocathode allows the imaging performances optimization. To this aim CsI(Tl) arrays pixel light distributions were investigated by using a photographic method and a Hamamatsu multianode 16 channel linear array photomultiplier tube for single-event light output readout. Ten scintillating arrays, with square pixel base area ranging between 1.0×1.0 and 2.0×2.0 mm 2 and thickness from 1.0 to 5.0 mm, were tested. In this study, the strip scintillation light distribution spread at photocathode was found linearly dependent on the total light guide thickness and crystal-pixel base side.

Images obtained by flood-field Co57 irradiation of CsI(Tl) crystal arrays detectors, coupled to a metal-channel dynode PSPMT, were statistically analyzed by means of a bivariate normal distribution. For each crystal position, the planar distribution charge was described by a confidence ellipse chosen to maximize the 1-to-1 relationship between the photons incoming at each crystal and the centroid obtained from electric charge distribution. The flood-field irradiation response of a 22 mm×22 mm CsI(Tl) array, with different pixel dimensions, were studied, and the comparison between the charge distribution of a limited number of crystals following the flood-field irradiation was made.

In the last 40 years, in the field of Molecular Medicine imaging there has been a huge growth in the employment and in the improvement of detectors for PET and SPECT applications in order to reach accurate diagnosis of the diseases. The most important feature required to these detectors is an high quality of images that is usually obtained benefitting from the development of a wide number of new scintillation crystals with high imaging performances. In this contest, features like high detection efficiency, short decay time, great spectral match with photodetectors, absence of afterglow and low costs are surely attractive. However, there are other factors playing an important role in the realization of high quality images such as energy and spatial resolutions, position linearity and contrast resolution. With the aim to realize an high performace gamma ray detector for PET and SPECT applications, this work is focused on the evaluation of the imaging characteristics of a recently developed scintillation crystal, CRY019.

The growing interest for new scintillation crystals with outstanding imaging performances (i.e. resolution and efficiency) has suggested the study of recently discovered scintillators named CRY018 and CRY019. The crystals under investigation are monolithic and have shown enhanced characteristics both for gamma ray spectrometry and for Nuclear Medicine imaging applications such as the dual isotope imaging. Moreover, the non-hygroscopic nature and the absence of afterglow make these scintillators even more attractive for the potential improvement in a wide range of applications. These scintillation crystals show a high energy resolution in the energy range involved in Nuclear Medicine, allowing the discrimination between very close energy values. Moreover, in order to prove their suitability of being powerful imaging systems, the imaging performances like the position linearity and the intrinsic spatial resolution have been evaluated obtaining satisfactory results thanks to the implementation of an optimized algorithm for the images reconstruction.

Recently scintillating crystals with high light yield coupled to photodetectors with high quantum efficiency have been opening a new way to make gamma cameras with superior performances based on continuous crystals. In this work we propose the analysis of a gamma camera based on a continuous LaBr3:Ce crystal coupled to a multi-anodes photomultiplier tube (MA-PMT). In particular we take into account four detector configurations, different in crystal thicknesses and assembling. We utilize a new position algorithm to reduce the position non linearity affecting intrinsic spatial resolution of small FoV gamma cameras when standard Anger algorithm is applied. The experimental data are obtained scanning the detectors with 0.4 mm collimated 99 m Tc source, at 1.5 mm step. An improvement in position linearity and spatial resolution of about a factor two is obtained with the new algorithm. The best values in terms of spatial resolution were 0.90 mm, 0.95 mm and 1.80 mm for integral assembled, 4.0 mm thick and 10 mm thick LaBr3:Ce crystal respectively.

We have developed a SPEMT (Single Photon Emission MammoTomography) scanner that is made up of two cameras rotating around the pendulous breast of the prone patient, in Vertical Axis of Rotation (VAoR) geometry. Monte Carlo simulations indicate that the device should be able to detect tumours of 8 mm diameter with a tumour/background uptake ratio of 5:1. The scanner field of view is 41.6 mm height and 147 mm in diameter. Each head is composed of one pixilated NaI(Tl) crystal matrix coupled to three Hamamatsu H8500 64-anodes PMT’s read out via resistive networks. A dedicated software has been developed to combine data from different PMT’s, thus recovering the dead areas between adjacent tubes. A single head has been fully characterized in stationary configuration both in active and dead areas using a point-like source in order to verify the effectiveness of the readout method in recovering the dead regions. The scanner has been installed at the Nuclear Medicine Division of the University of Pisa for its validation using breast phantoms. The very first tomographic images of a breast phantom show a good agreement with Monte Carlo simulation results.

Mammoscintigraphy is an important tool for secondary breast cancer screening. Good results have been achieved with dedicated gamma cameras for T 1b tumors (size >5 mm). We have performed simulations and measurements in order to improve the performance of compact gamma cameras for detecting T 1a tumors (size 3 ) coupled with a Position Sensitive Photomultiplier Tube (PSPMT) having a multianode structure (2×2 mm 2 pad size). Measurements allowed to test the validity of the simulation software.

The principal limiting factor in the clinical acceptance of scintimammography is certainly its low sensitivity for cancers sized

Over the last three years, there has been a growing interest in the development of a new class of fast scintillators such as LaCl3 :Ce and LaBr3:Ce, or their superior energy resolution is opening an easier way to improve spatial resolution. In this paper we present the results obtained from the first LaBr3:Ce small gamma camera. It is based on continuous 50 times 50 mm2 crystal 5 mm thick integral assembled with a Hamamatsu Flat panel PMT. This detector optical configuration permits the narrowest light distribution and highest light collection to obtain the best spatial and energy resolution values respectively. At the same time 5 mm crystal thickness carries out 80% efficiency at 140 keV photon energy. Measurements of spatial resolution are also compared with the analogous ones obtained from another 50 times 50 mm2 LaBr3:Ce crystal, assembled with a 3 mm glass optical window. Energy resolution values have been furtherly compared with ones obtained from a LaBr3:Ce one inch diameter and thickness optimized for spectrometric measurements. The first LaBr3:Ce gamma camera shows excellent intrinsic spatial resolution values such as 0.9 mm with a best energy resolution value of 6.0% at 140 keV photon energy

Molecular imaging with radionuclides is a very sensitive technique because it allows to obtain images with nanomolar or picomolar concentrations. This has generated a rapid growth of interest in radionuclide imaging of small animals. Indeed radiolabeling of small molecules, antibodies, peptides and probes for gene expression enables molecular imaging in vivo, but only if a suitable imaging system is used. Detecting small tumors in humans is another important application of such techniques. In single gamma imaging, there is always a well known tradeoff between spatial resolution and sensitivity due to unavoidable collimation requirements. Limitation of the sensitivity due to collimation is well known and affects the performance of imaging systems, especially if only radiopharmaceuticals with limited uptake are available. In many cases coded aperture collimation can provide a solution, if the near field artifact effect can be eliminated or limited. At least this is the case for “small volumes” imaging, involving small animals. In this paper 3D-laminography simulations and preliminary measurements with coded aperture collimation are presented. Different masks have been designed for different applications showing the advantages of the technique in terms of sensitivity and spatial resolution. The limitations of the technique are also discussed.

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.

The bimodal diagnostic systems like ultrasound/scintigraphic ones have the benefit of providing both morphological and physiological information. In the case in which it intends to develop a compact bimodal probe it is important that, as the readout electronics are doubled, the acquisition system is the most compact possible. In this paper we present the characterization and preliminary measurements on a multi-channel readout ASIC for PSPMTs. The chip is equipped with 32 readout channels, as different works show that single channel readout allows to exploit the performances of a gamma detector, especially for linearity. Each single channel readout is composed by a variable capacitor CSA, a sample&hold and a variable gain amplifier (VGA). The possibility to change the gain of the amplifier allows to compensate for the differences in gain of the anodes of the PSPMT, while the possibility of changing the integrator capacitor allows to adapt the input dynamic of the chip depending on the PMT used (BA or SBA photocatode) and on the scintillation crystal coupled to the PMT itself. The preliminary measurements show that a 200 kHz maximum sampling rate is achievable, with 1 V input dynamic and an overall linearity of the whole channel with respect to the input charge impulse of than 2%. To validate the performances of the ASIC different operative measurement was made in two configurations: with a single chip and two R11265-M16 PMTs, and, parallelizing two chips with a single PMT H8500. The tubes were coupled with scintillation crystals with different response speeds, from CsI to LaBr3.

In the last few years, integrated multi-modality systems have been developed, aimed at improving the accuracy of medical diagnosis correlating information from different imaging techniques. In this contest, a novel dual modality probe is proposed, based on an ultrasound detector integrated with a small field of view single photon emission gamma camera. The probe, dedicated to visualize small organs or tissues located at short depths, performs dual modality images and permits to correlate morphological and functional information. The small field of view gamma camera consists of a continuous NaI:Tl scintillation crystal coupled with two multi-anode photomultiplier tubes. Both detectors were characterized in terms of position linearity and spatial resolution performances in order to guarantee the spatial correspondence between the ultrasound and the gamma images. Finally, dual-modality images of custom phantoms are obtained highlighting the good co-registration between ultrasound and gamma images, in terms of geometry and image processing, as a consequence of calibration procedures.

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 recent improvements in the quantum efficiency of Hamamatsu H8500 position sensitive PMT can be exploited if a multi channel low-noise readout electronics is used. In order to test to its limits the capability of the H8500 and readout electronic system, the PSPMT is coupled with an integral line NaI(Tl) crystal 1.5 mm thick, a pixellated NaI(Tl) 2.0mm pitch, 6mm thick and a pixellated CsI(Tl), 1mm pitch, 1mm thick. The gamma camera with the different crystals is tested with gamma sources in the 30 to 660 keV energy range. The acquisition system used is made by four analog PCBs, each one makes the acquisition of the analog signal and the A/D conversion from 16 anodes at 14 bit resolution, and is connected by USB to a control PC. The aim of the measurements is to show that, as expected from poisson statistic, the spatial resolution and the size of the PSF (sigma of the distribution of light) are inversely proportional to the square root of the photocathode generated photoelectron number. The values measured in the two configurations (continuous integral line and pixelated crystal) are compatible with those expected. Particularly, for the pixellated NaI(Tl) we find a Gaussian light distribution with about 11 mm FWHM and a with a source at 140 keV we can estimate a photo electron yield equal to 600–800 per scintillating event, with an estimated resolution close to 0.35–0.50 mm. The gamma camera is able to correctly identify the light distribution also with 1 mm pixellated CsI(Tl) where the light distribution is virtually contained in a single anode (the anode dimension is 6 mm by 6 mm) and the assignment of the correct position is only estimated based on the very low levels of charge present on the anodes around the one that collected the most of the charge.

The public domain code GENIA, based on multi-printing method for producing surface sources with appropriate radioactivity, is described. The conventional technique, running on standard inkjet printer with radio-marked ink filling, is improved by repeating elementary printing commands in the same band. Well outlined sources with adjustable radioactivity can be obtained without refilling. The intrinsic limitation of printable radioactivity, depending on the value available at nozzles at printing time, was overcome. In addition the method permits the accurate calibration of the amount of activity released onto the paper.

The aim of this work is to present a 64-independent channels, low noise and wide dynamic range readout system for multi-anodes photo-multiplier tubes (MA-PMTs). The results consist of some imaging tests obtained with a Hamamatsu H8500 MA-PMT coupled to different scintillation crystals, like a LaBr3(Ce) continuous crystal and NaI(Tl), CsI(Tl) and YAP pixilated scintillation arrays. Moreover, the Hamamatsu H8500C-Mod8 new series equipped with a super bialkali (SBA) photocatode was also studied. Energy and spatial resolutions showed an improvement with respect to the previous generation of multi-channel read-out electronics and we also reported some very interesting results with LaBr3(Ce) crystal coupled to the new Hamamatsu H8500-Mod8 with high quantum efficiency. That demonstrated the excellent response characteristics and versatility of our proposed electronic system and its potential use with all γ-ray detectors.

The gamma cameras built on a LaBr3 crystal and Hamamatsu H8500 has a 49 mm by 49 mm FOV, equal to the detector active area. In order to increase the active area it is necessary to put more than one detector side to side. This can be done because the H8500 is designed do reduce as much as possible the dead area between two detectors. If we use a 2 by 2 matrix it is possible to use a single 10cm by 10 cm LaBr3 crystal. The readout system has in this case 256 independent channels, with low noise and wide dynamic. The system is managed by an FPGA that reads all the inputs in parallel, up to a maximum rate of 250 KSample/sec, and makes a pre-processing of data. The use of the last generation H8500 PSPMTs, having a SBA photocatode with better quantum efficiency but a lower gain, requires an in deep analysis on the readout electronics induced error, in order to increase the signal to noise ratio. Moreover the individual channel readout allows a better correction of the anodic gains, a particularly relevant problem when more than one PMT is used, and a better study of the light sharing among two PMTs by the use of more sophisticated algorithms with respect to standard the CoG. This approach is mandatory in order to reduce the dead zone between two PMTs.

The position sensitivity of two large volume (1” × 1” and 3” × 3”) LaBr 3 :Ce crystals has been measured using collimated beams of 662 keV γ-rays. The crystals have been coupled to a Position Sensitive Photo Multiplier Tube (PSPMT) and/or shielded phototube. The results indicate that, in the case of 662 keV γ -rays, both crystals should allow identification of the the position of the γ-ray first interaction with a 1-2 cm resolution. Similar tests have been done in the past using 140 keV γ-rays and no sensitivity was found. Using GEANT4 simulations we confirmed these results.

In the development of a new gamma camera, we compare the characteristic of two distinct readout electronics, both able to perform single anode reading. The two gamma cameras are based on the H8500 Position Sensitive Photomultiplier (PSPMT) coupled with a planar 5cm × 5cm × 0.4cm BrLa 3 :Ce crystal.

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.

Knowledge of the Depth-Of-Interaction (DOI) in detector is crucial for small ring diameter PET scanner but it is also very important for single photon emission imaging, in particular for applications where very high spatial resolution is required and position distortions caused by slant collimators can strongly affect the final response of the 3D reconstructed image. In addition the DOI determination at 140 keV is the most critical due to thinner crystal thickness and the lower number of scintillation light photons. Continuous scintillation crystals are in principle the most suitable for continuous DOI determination based on the measurements of light width of cones generated at each gamma ray interaction. In this work we propose an analysis based on a Monte Carlo GEANT4 studies and on experimental measurements at 140 keV performed on a small LaBr3:Ce continuous crystal coupled to latest multi-anode PMT Hamamatsu H8500-MOD8 series equipped with super Bialkali photocathode (SBA). The basic idea of this work is that the high light output of LaBr 3 :Ce joint with SBA photodetector can reduces statistical uncertainties related to the light distribution spread determination. Furthermore it can be crucial with a more precise measurement of scintillation light distribution from the 8×8 anode array of MAPMT. Measurements and simulation confirm that light distribution spread (SD) is related to DOI, with a DOI resolution of about 2.0-2.2 mm (Monte Carlo) and 2.8-3.0 mm experimental at 140 keV. In addition, we shown how the selection in SD window provide a 10% of spatial resolution improvement, down to (0.85±0.03) mm, for a LaBr 3 (Ce) continuous crystal coupled to the new photodetector H8500-MOD8. This method can open the possibility to build a high-sensitivity detector with DOI capability useful for gamma-ray imaging application.

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

In this work we propose an analysis of a novel Low Energy (LE) parallel hole collimator for high resolution SPET applications. The tested prototype, realized jointly with Nuclear Fields, is a lead parallel hole collimator with 1.0 mm hexagonal hole, 18 mm length, 0.2 mm septa and 10x10 cm2 of useful detection area. It was planned to match the high spatial resolution performances of a compact gamma camera based on LaBr3(Ce) continuous scintillation crystal. The imaging performance of this prototype is compared with a tungsten pinhole collimator (1.0 mm diameter) and with a couple of 1.5 mm parallel hole collimators, 22 mm and 40 mm length with 0.2 mm septa respectively. All the collimators were individually coupled to a scintillation gamma camera based on LaBr3(Ce) continuous crystal and multi anode PMT Hamamatsu H8500. The high intrinsic spatial resolution of the crystal enhances the response of collimators at short source-to-collimator distance –SCD overcoming problems in alignment with the collimator pattern. Spatial resolution and sensitivity were evaluated by scanning the detector field of view at different SCD using a Co57 point source. The parallel hole prototype showed SR better than pinhole with 28 mm FoV. In term of sensitivity, it showed values greater than pinhole one at FoV larger than 2.4 cm. In comparison with LEHR parallel hole collimators, the prototype carried out better SR values at SCD lower than 20 mm with two times more sensitivity. Moreover, the overall SR improved of 20% with respect to the LEGP one at all SCD, with only 35% loss of sensitivity. The collimator prototype seemed complementary with the use of pinhole one and in addition when coupled to the compact LaBr3(Ce) gamma camera can allow a very attractive trade-off between spatial resolution, sensitivity and detection area for radionuclide molecular imaging applications.