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Nuclear Science, IEEE Transactions on

Issue 5 • Date Oct. 2010

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Displaying Results 1 - 25 of 32
  • [Front cover]

    Page(s): C1
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  • IEEE Transactions on Nuclear Science publication information

    Page(s): C2
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  • Table of contents

    Page(s): 2409 - 2410
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  • Factors Influencing Time Resolution of Scintillators and Ways to Improve Them

    Page(s): 2411 - 2416
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1095 KB) |  | HTML iconHTML  

    The renewal of interest in Time of Flight Positron Emission Tomography (TOF-PET), as well as the necessity to precisely tag events in high energy physics (HEP) experiments at future colliders are pushing for an optimization of all factors affecting the time resolution of the whole acquisition chain comprising the crystal, the photo detector, and the electronics. The time resolution of a scintillator-based detection system is determined by the rate of photo electrons at the detection threshold, which depends on the time distribution of photons being converted in the photo detector. The possibility to achieve time resolution of about 100 ps Full Width at Half Maximum (FWHM) requires an optimization of the light production in the scintillator, the light transport and its transfer from the scintillator to the photo detector. In order to maximize the light yield, and in particular the density of photons in the first nanosecond, while minimizing the rise time and decay time, particular attention must be paid to the energy transfer mechanisms to the activator as well as to the energy transition type at the activator ion. Alternatively other light emission mechanisms can be considered. We show that particularly Cerenkov emission can be used for this purpose. Special emphasis was put on the light transport within the crystal and at its interface with the photo detector. Since light is produced isotropically in the scintillator the detector geometry must be optimized to decrease the optical path-length to the photo detector. Moreover light bouncing within the scintillator, affecting about 70% of the photons generated in currently used crystals, must be reduced as much as possible. We also investigate photonics crystals that are specifically designed to favor specific light propagation modes at the limit of total reflection inside and outside of the crystal and how they might increase the light transfer efficiency to the photo detector and hence improve time resolution. Exampl- - es for the production and deposition of photonics crystals as layers on Lutetium Yttrium Ortho-Silicate (LYSO) and Lutetium Yttrium Aluminum Perovskite (LuYAP) crystals are shown here, as well as first results on an improved light extraction resulting from this method. View full abstract»

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  • Investigation of a Multi-Anode Microchannel Plate PMT for Time-of-Flight PET

    Page(s): 2417 - 2423
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    We report on an investigation of a mulit-anode microchannel plate PMT for time-of-flight PET detector modules. The primary advantages of an MCP lie in its excellent timing properties (fast rise time and low transit time spread), compact size, and reasonably large active area, thus making it a good candidate for TOF applications. In addition, the anode can be segmented into an array of collection electrodes with fine pitch to attain good position sensitivity. In this paper, we investigate using the Photonis Planacon MCP-PMT with a pore size of 10 μm to construct a PET detector module, specifically for time-of-flight applications. We measure the single electron response by exciting the Planacon with pulsed laser diode. We also measure the performance of the Planacon as a PET detector by coupling a 4 mm×4 mm×10 mm LSO crystal to individual pixel to study its gain uniformity, energy resolution, and timing resolution. The rise time of the Planacon is 440 ps with pulse duration of about 1 ns. A transit time spread of 120 ps FWHM is achieved. The gain is fairly uniform across the central region of the Planacon, but drops off by as much as a factor of 2.5 around the edges. The energy resolution is fairly uniform across the Planacon with an average value of 18.6 ± 0.7% FWHM. While the average timing resolution of 252 ± 7 ps FWHM is achieved in the central region of the Planacon, it degrades to 280 ± 9 ps FWHM for edge pixels and 316 ± 15 ps FWHM for corner pixels. We compare the results with measurements performed with a fast timing conventional PMT (Hamamatsu R-9800). We find that the R9800, which has significantly higher PDE, has a better timing resolution than the Planacon. Furthermore, we perform detector simulations to calculate the improvement that can be achieved with a higher PDE Planacon. The calculation shows that the Planacon can achieve significantly better timing resoluti- - on if it can attain the same PDE as the R-9800, while only a 30% improvement is needed to yield a similar timing resolution as the R-9800. View full abstract»

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  • Characterization of Silicon Detectors for the SiliPET Project: A Small Animal PET Scanner Based on Stacks of Silicon Detectors

    Page(s): 2424 - 2436
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    In this paper we propose a new scanner for small animal positron emission tomography (PET) based on stacks of double sided silicon detectors. Each stack is composed of 40 planar detectors with dimension 60 mm x 60 mm x 1 mm and 128 orthogonal strips on both sides to read the two coordinates of interaction, the third being the detector number in the stack. Multiple interactions in a stack are discarded. In this way we achieve a precise determination of the first interaction point of the two 511 keV photons. The price to pay is an efficiency reduction for each stack of about 50%. The reduced dimensions of the scanner also improve the solid angle coverage resulting in a high sensitivity. Preliminary results were obtained with the MEGA prototype tracker. Here, we report on the results obtained with double sided silicon prototype detectors, manufactured by ITC-FBK, having an active area of 3 cm X 3 cm and a strip pitch of 500 μm. Two different strip widths of 300 μm and 200 μm, and two thicknesses of 1 mm and 1.5 mm, equipped with 64 orthogonal p and n strips on opposite sides were read out with the VATAGP2.5 ASIC, a 128channel "general purpose" charge sensitive amplifier. We describe the experimental setup, the measurements and the results in terms of spatial resolution, spectral and timing performances obtained with the prototype detectors. View full abstract»

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  • Effects of the Super Bialkali Photocathode on the Performance Characteristics of a Position-Sensitive Depth-of-Interaction PET Detector Module

    Page(s): 2437 - 2441
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    Super Bialkali (SBA) photocathode is a new technology that improves the spectral response characteristics of position sensitive PMTs, boosting their quantum efficiency up to 35%. In this experiment, two SBA tubes were introduced into a production line of PET detectors mixed with the regular tubes. The detectors were assembled using the standard factory protocols for detector mounting, calibration and testing. We report an evaluation of the improvement introduced by the SBA photocathode comparing the spatial and energy resolution and the depth-of-interaction (DOI) performance of PET detector modules with DOI capabilities. We conclude that the superior performance of the SBA tube may enable the use of arrays with a larger number of crystals of smaller footprint, thus potentially improving the detector intrinsic spatial resolution without degrading the energy resolution or the phoswich (DOI) discrimination capability. View full abstract»

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  • Evaluation of a 1024 Anodes Micro-Channel Plate PMT for Preclinical PET Imaging

    Page(s): 2442 - 2447
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    A new generation of flat panel photomultiplier tube (PMT) based on micro-channel plates (MCP) offers characteristics suitable for PET imaging. We are developing a preclinical PET system composed of four detection modules arranged around the animal. Each module consists in 768 LYSO:Ce crystals read at both ends by MCP-PMT. The particular geometry combined with an inner diameter of 61.2 mm lead to a high detection efficiency with a volumetric spatial resolution of 1 μL. The purpose of this work is to characterize the 1024 anodes of the MCP-PMT (Planacon XP85023/A1, Photonis Corp.) used in our preclinical PET system. The Planacon has very compact size (58 × 58 × 13.7 mm3) with an active area of 53 × 53 mm2. The anode array consists in a 32 × 32 matrix in which each individual anode is 1.4 × 1.4 mm2 with a pitch of 1.6 mm. Due to the lack of backside connectors and in order to individually readout the anode current, a dedicated connection board has been developed. The dark current, the gain and the timing resolution of one anode are measured as well as the charge sharing, the gain uniformity and the intrinsic spatial resolution on the entire active field of view. With a timing resolution below 100 ps, an intrinsic spatial resolution of 400 μm, a low dark current and a high gain, the Planacon XP85023/A1 offers a promising photodetector for PET imaging. View full abstract»

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  • Development of an APD-Based PET Module and Preliminary Resolution Performance of an Experimental Prototype Gantry

    Page(s): 2448 - 2454
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1234 KB) |  | HTML iconHTML  

    The development of a high-resolution Positron Emission Tomography (PET) technique with sub-millimeter spatial resolution, which utilizes newly designed reverse-type APD-arrays, is uderway. All the detector blocks are modularized with the overall dimension of each module, including the APD array, LYSO scintillator matrix and Front-End Circuits (FECs), which are only 30 × 30 × 80 mm3. Each APD device also has a monolithic 16 × 16 pixel structure with an active area of 1.0 mm2 per pixel. The FEC includes two identical analog ASICs specifically designed for APDs with a noise characteristic of 560 + 30 e-/pF and a timing resolution of 460 ps (rms), respectively. An energy resolution of 13.7 ± 1.1% (FWHM) with 662 keV gamma-rays was measured using the 16 × 16 arrays. At this stage a pair of module and coincidence circuits has been assembled into an experimental prototype gantry. Spatial resolutions of 0.9, 1.4, and 1.3 mm (FWHM) were obtained from FBP reconstructed images in preliminary experiments with a point source positioned centrally, and 1 and 5 mm off-center, respectively. Comparison with a Monte-Carlo simulation of a fully-designed gantry over a wider range of field-of-view showed good correlation with the experimental data. A simple but conceptual design of a DOI configuration is also proposed as a test example of a future APD-PET scanner. View full abstract»

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  • Development of PET Detectors Using Monolithic Scintillation Crystals Processed With Sub-Surface Laser Engraving Technique

    Page(s): 2455 - 2459
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    New monolithic scintillation detectors for PET have been developed, where the crystals are processed using an internally focused laser processing technique called sub-surface laser engraving (SSLE). When high intensity light pulses of short duration from a laser are focused into a scintillation crystal, they induce multi-photon absorption at the focal point and result in refractive index changes or micro-cracks inside the crystal. By applying the SSLE technique to a monolithic scintillation block, fine segmentation in the crystal can be formed without inter-pixel gaps. We have fabricated 2D segmented arrays by using a Nd:YAG laser to engrave various patterns of micro-cracks inside monolithic LYSO crystal blocks. The processed crystal array, segmented to 12 × 12 with 1.67 mm pitch, has been evaluated by coupling to a position-sensitive photomultiplier tube (PS-PMT). The 2D position histograms were measured for uniform irradiation of gamma rays, and each crystal segment was clearly separated. The average energy resolution was 9.7%, similar to that of the conventional arrays, so the laser-processed LYSO crystals have kept their primary scintillation properties. We have also evaluated the laser-processed crystals by using multi-pixel photon counters (MPPCs) to investigate their possibility as a future PET detector. The results suggest that it is possible to fabricate high performance PET detectors using the SSLE technique. View full abstract»

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  • Validation of Detect2000-Based PetDetSim by Simulated and Measured Light Output of Scintillator Crystal Pins for PET Detectors

    Page(s): 2460 - 2467
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (570 KB) |  | HTML iconHTML  

    A new Monte Carlo simulation tool, called PetDetSim and its experimental validation is presented. The simulation environment aims to model PET detectors and applies the Detect2000 code. Light output of LYSO and GSO crystal pins of different size and surface finish, covered with diffuse or specular reflectors was experimentally determined and compared with the results of the simulations. By improving the model concerning the pin and reflector geometry and the wavelength dependent reflection of the photocathode, the figure of merit could be considerably improved. The initially 34% deviation between simulation and measurements decreased below 11% for all LYSO crystal configurations. View full abstract»

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  • Optimizing PET DOI Resolution With Crystal Coating and Length

    Page(s): 2468 - 2474
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (737 KB) |  | HTML iconHTML  

    In the last few years, one of the main research programs for PET systems has been the improvement of spatial resolution using Depth Of Interaction (DOI) information. In the context of developing a new PET system dedicated to small animals with axially oriented LYSO crystals and DOI capability, we have investigated the influence of the crystal coating and its length on the DOI resolution. The proposed PET system is composed of four detection modules arranged around the animal. Each module consists in 768 LYSO crystals read at both ends by multichannel plate photodetectors. The particular geometry combined with an inner diameter of 61.2 mm, lead to high detection efficiency close to the system solid angle. The LYSO crystal is chosen for its light yield of 33 ph/keV and its attenuation length of 11.2 mm at 511 keV. To obtain a transverse spatial resolution of 1 mm, the section of the crystal was fixed to 1.5 mm. To achieve a DOI resolution close to 1 mm, measurements have been performed on different LYSO crystal coatings with a length ranging from 25 mm to 35 mm. Each crystal is positioned on an xy translation stage and read out at both ends by H3164-10 Hamamatsu PMTs. The DOI information is then derived every 0.5 mm along the crystal extent. The use of an electronic collimation leads to a 22Na source beam size of (1.58 ± 0.04) mm reaching the crystal. The optimized coating in terms of packing fraction and DOI resolution is found to be a mixture made with 30% TiO2 powder in a PMMA binder. With this appropriate coating, an average DOI resolution of (0.82 ± 0.13) mm can be achieved with a 25 mm crystal length using a 20% photopeak energy window. The resolution degrades to (1.39 ± 0.16) mm when a wide-open energy window is used. Those values are corrected for the source beam size. Using this experimental proposal, a matrix of LYSO crystals has been built reaching a packing fraction of 93%. In this study, we demonstrate that us- - ing a 1.5 × 1.5 × 25 mm3 LYSO crystal, a DOI resolution of less than a millimeter can be achieved while keeping a high packing fraction for a system detection efficiency close to 15%. View full abstract»

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  • Improving Light Extraction From Heavy Inorganic Scintillators by Photonic Crystals

    Page(s): 2475 - 2482
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1002 KB) |  | HTML iconHTML  

    The impact of photonic crystal (PhC) slabs on the extraction of light from the heavy inorganic scintillators LuYAP and LYSO is evaluated by combining numerical transmission calculations of a scintillator with PhC coupling face with simulations of the light propagation inside the scintillator. The transmission of the scintillator-PhC coupling face is determined by means of a scattering-matrix algorithm. The PhC slab is assumed to consist of a bulk material with a triangular pattern of air holes that is sandwiched between the scintillator substrate and a layer of optical grease. By folding these data with the angular distribution of the scintillation photons arriving at the coupling face, the light collection efficiency ηL of the system is estimated. The results indicate that a scintillator coupling face equipped with a PhC slab can exhibit a significant gain in ηL. This gain is due to the extraction of photons that are lost in a scintillator with plain exit surface due to total internal reflection. The largest simulated gains of up to a factor of two are observed for small scintillators and for PhC coupling faces with nbulknsub, navg ≈ √(nsub·ngrease), and da, where nbulk, nsub and ngrease are the respective refractive indexes of the PhC bulk, the scintillator substrate, and the optical grease, a the lattice constant of the PhC pattern, d the thickness of the PhC slab, and navg the average refractive index of the PhC slab determined by nbulk and the filling factor f. Due to the approximations and idealizations of the model, these gains in light collection efficiency may be lower in practical applications and are expected to be achieved only with specular reflectors with reflectivit- - ies above 90%, and PhC bulk materials with absorption coefficients αabs ≤ 103-104 cm-1 over the whole wavelength range of emission of the scintillator. View full abstract»

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  • A Time Efficient Optical Model for GATE Simulation of a LYSO Scintillation Matrix Used in PET Applications

    Page(s): 2483 - 2489
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    A time efficient optical model is proposed for GATE simulation of a LYSO scintillation matrix coupled to a photomultiplier. The purpose is to avoid the excessively long computation time when activating the optical processes in GATE. The usefulness of the model is demonstrated by comparing the simulated and experimental energy spectra obtained with the dual planar head equipment for dosimetry with a positron emission tomograph (DoPET). The procedure to apply the model is divided in two steps. Firstly, a simplified simulation of a single crystal element of DoPET is used to fit an analytic function that models the optical attenuation inside the crystal. In a second step, the model is employed to calculate the influence of this attenuation in the energy registered by the tomograph. The use of the proposed optical model is around three orders of magnitude faster than a GATE simulation with optical processes enabled. A good agreement was found between the experimental and simulated data using the optical model. The results indicate that optical interactions inside the crystal elements play an important role on the energy resolution and induce a considerable degradation of the spectra information acquired by DoPET. Finally, the same approach employed by the proposed optical model could be useful to simulate a scintillation matrix coupled to a photomultiplier using single or dual readout scheme. View full abstract»

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  • A Low Noise Pixel Architecture for Scientific CMOS Monolithic Active Pixel Sensors

    Page(s): 2490 - 2496
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    This paper presents the design and characterisation of FORTIS (4T Test Image Sensor), which is a low noise, CMOS monolithic active pixel sensor for scientific applications. The pixels present in FORTIS are based around the four transistor (4T) pixel architecture, which is already widely used in the commercial imaging community. The sensor design contains thirteen different variants of the 4T pixel architecture to investigate the effects of changing its core parameters. The variants include differences in the pixel pitch, the diode size, the in-pixel source follower, and the capacitance of the floating diffusion node (the input node of the in-pixel source follower). Processing variations have also been studied, which include varying the resistivity of the epitaxial layer and investigating the effects of a special deep p-well layer. By varying these parameters, the 4T pixel architecture can be optimised for scientific applications where detection of small amounts of charge is required. View full abstract»

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  • Imaging Studies for Evaluating Impact of Position Sampling Techniques in PET Scanners

    Page(s): 2497 - 2503
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2529 KB) |  | HTML iconHTML  

    Previously we have evaluated two crystal calibration techniques that can be applied to pixelated detector designs to improve system spatial resolution without detector motion. The inter-crystal positioning technique utilizes sub-sampling in the crystal flood map to better sample the Compton scatter events in the detector. The Compton scatter rejection technique, on the other hand, rejects those events that are located further from individual crystal centers in the flood map. Here we performed imaging studies with a Mini Deluxe hot rod phantom and a hot sphere phantom (sphere diameters of 4.95 and 7.86-mm with 6:1 uptake relative to background) using the standard crystal calibration technique, as well as the inter-crystal and Compton rejection calibration techniques. Our results show improved separation of 1.6-mm diameter hot rods with the two new crystal calibration techniques that is consistent with improved spatial resolution. For the hot sphere phantom the contrast recovery is improved with both the inter-crystal and Compton rejection calibration techniques over the standard calibration technique. The only drawback of the inter-crystal calibration technique is the increase in the number of possible lines-of-response (LORs) (factor of 16) that may slow image reconstruction. With the Compton rejection calibration technique, loss of counts leads to increased noise in the images. View full abstract»

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  • A Breast Phantom Lesion Study With the High Resolution Transformable HOTPET Camera

    Page(s): 2504 - 2509
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2489 KB) |  | HTML iconHTML  

    The high-resolution oncologic transformable PET (HOTPET) camera can operate in different modes including breast mode and whole-body mode. In the whole-body mode, HOTPET has a transverse field-of-view (FOV) of 60 cm and an axial FOV of 13 cm. In the breast mode it has a transverse FOV of 39 cm and an axial FOV of 21 cm. The aim of this study was to compare the performance of the two modes of HOTPET for observation of small ( <; 10 mm) breast lesions to measure the effective gain in lesion detection by using a dedicated breast ring PET. We compared the two modes of camera by scanning a breast phantom with small lesion insert. The breast phantom was attached to an anthropomorphic torso phantom with lung and cardiac inserts. We scanned several small lesions with inner diameters in the range of 3.95 mm to 7.86 mm for several lesion activity contrasts. The ratio of the activity concentration in the lesions to the activity concentration in the breast background ranged from 1 to 10. Reconstructed images of lesions were compared visually and we also compared the image contrast of lesions and radial profiles of lesions. The 7.86-mm lesion was observable for lesion to breast background activity ratio of 2.2 or higher in HOTPET breast mode and for activity ratio of 3.1 or higher in the whole-body mode. The 4.95-mm lesion was observable for activity ratio of 3.1 in the breast mode and activity ratio of 6.9 in whole-body mode. The 3.95-mm lesion was visually observable for activity ratio of higher than 5 in the breast mode but it was not observable in whole-body mode even at the highest measured contrast. This study demonstrated that a whole-body PET camera such as HOTPET even with 2.9-mm spatial resolution may not be able to detect lesions smaller than 7 mm for lesion to background activity ratio 3.5, while a dedicated full ring breast PET similar to HOTPET breast mode could detect smaller lesions (≤ 5 mm) for similar uptake. View full abstract»

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  • Evaluation of Scattering in Cone-Beam Breast Computed Tomography: A Monte Carlo and Experimental Phantom Study

    Page(s): 2510 - 2517
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    In this paper Monte Carlo simulations were performed for X-ray irradiations of breast phantoms of various sizes such as PMMA cylinders of different diameters and a hemi-ellipsoidal PMMA phantom. The aim was the evaluation of the 2D distribution of primary and scattered photons and Scatter-to-Primary Ratio (SPR) in projection images in cone-beam breast Computed Tomography (CT). Irradiation geometry and technique factors reproduce the experimental conditions used for validation measurements with a prototype CT breast scanner. Simulations were performed with GEANT4 software. We varied the phantom diameter and shape, the X-ray tube voltage and added filtration. Magnification was 1.31. SPR increases from 0.4 (at 8 cm cylinder diameter) up to 1.5 (14 cm cylinder diameter) at the centre of the phantom. In the same phantom, SPR has lower values toward the bases of the cylinder than at its centre. The scatter component increases by adopting a 50 kVp or higher tube voltages, up to 80 kVp, and by increasing the added filtration. Simulated and measured lateral profiles across a 14 cm cylinder diameter in projection images show a relative deviation of 4%. Simulations show a different distribution of scatter and SPR in a 14 cm diameter cylinder and 14 cm hemi-ellipsoidal phantom, so questioning the use of simple cylindrical geometries when simulating the attenuation of the pendant breast for scatter correction procedures. The strength and the non-uniformity of the SPR inside the cylindrical phantom decrease as the size of the air gap between object and detector increases. View full abstract»

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  • Phantom Experiments on a PSAPD-Based Compact Gamma Camera With Submillimeter Spatial Resolution for Small Animal SPECT

    Page(s): 2518 - 2523
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    We demonstrate a position sensitive avalanche photodiode (PSAPD) based compact gamma camera for the application of small animal single photon emission computed tomography (SPECT). The silicon PSAPD with a two-dimensional resistive layer and four readout channels is implemented as a gamma ray detector to record the energy and position of radiation events from a radionuclide source. A 2 mm thick monolithic CsI:Tl scintillator is optically coupled to a PSAPD with a 8 mm X 8 mm active area, providing submillimeter intrinsic spatial resolution, high energy resolution (16% full-width half maximum at 140 keV) and high gain. A mouse heart phantom filled with an aqueous solution of 370 MBq 99mTc-pertechnetate (140 keV) was imaged using the PSAPD detector module and a tungsten knife-edge pinhole collimator with a 0.5 mm diameter aperture. The PSAPD detector module was cooled with cold nitrogen gas to suppress dark current shot noise. For each projection image of the mouse heart phantom, a rotated diagonal readout algorithm was used to calculate the position of radiation events and correct for pincushion distortion. The reconstructed image of the mouse heart phantom demonstrated reproducible image quality with submillimeter spatial resolution (0.7 mm), showing the feasibility of using the compact PSAPD-based gamma camera for a small animal SPECT system. View full abstract»

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  • A SPECT Scanner for Rodent Imaging Based on Small-Area Gamma Cameras

    Page(s): 2524 - 2531
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1998 KB) |  | HTML iconHTML  

    We developed a cost-effective SPECT scanner prototype (rSPECT) for in vivo imaging of rodents based on small-area gamma cameras. Each detector consists of a position-sensitive photomultiplier tube (PS-PMT) coupled to a 30 x 30 Nal(Tl) scintillator array and electronics attached to the PS-PMT sockets for adapting the detector signals to an in-house developed data acquisition system. The detector components are enclosed in a lead-shielded case with a receptacle to insert the collimators. System performance was assessed using 99mTc for a high-resolution parallel-hole collimator, and for a 0.75-mm pinhole collimator with a 60° aperture angle and a 42-mm collimator length. The energy resolution is about 10.7% of the photopeak energy. The overall system sensitivity is about 3 cps/μCi/detector and planar spatial resolution ranges from 2.4 mm at 1 cm source-to-collimator distance to 4.1 mm at 4.5 cm with parallel-hole collimators. With pinhole collimators planar spatial resolution ranges from 1.2 mm at 1 cm source-to-collimator distance to 2.4 mm at 4.5 cm; sensitivity at these distances ranges from 2.8 to 0.5 cps/μCi/detector. Tomographic hot-rod phantom images are presented together with images of bone, myocardium and brain of living rodents to demonstrate the feasibility of preclinical small-animal studies with the rSPECT. View full abstract»

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  • OpenPET: A Flexible Electronics System for Radiotracer Imaging

    Page(s): 2532 - 2537
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (962 KB) |  | HTML iconHTML  

    We present the design for OpenPET, an electronics readout system designed for prototype radiotracer imaging instruments. The critical requirements are that it has sufficient performance, channel count, channel density, and power consumption to service a complete camera, and yet be simple, flexible, and customizable enough to be used with almost any detector or camera design. An important feature of this system is that each analog input is processed independently. Each input can be configured to accept signals of either polarity as well as either differential or ground referenced signals. Each signal is digitized by a continuously sampled ADC, which is processed by an FPGA to extract pulse height information. A leading edge discriminator creates a timing edge that is “time stamped” by a TDC implemented inside the FPGA. This digital information from each channel is sent to an FPGA that services 16 analog channels, and information from multiple channels is processed by this FPGA to perform logic for crystal lookup, DOI calculation, calibration, etc. As all of this processing is controlled by firmware and software, it can be modified/customized easily. The system is open source, meaning that all technical data (specifications, schematics and board layout files, source code, and instructions) will be publicly available. View full abstract»

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  • Time Resolution for Scattered and Unscattered Coincidences in a TOF PET Scanner

    Page(s): 2538 - 2544
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (706 KB) |  | HTML iconHTML  

    Time resolution is a key parameter in the performance of a Time-of-Flight (TOF) Positron Emission Tomography (PET) scanner, and it is usually measured in the system with unscattered data and used as the width of the TOF kernel in reconstruction. In fact, the time distribution of detected coincidence events is a function of the energy of the detected photons, and true and scatter events have different time distributions. While the reconstruction TOF kernel should match the true or unscattered data, the scatter simulation used for scatter correction should match the time distribution of the scatter data. This work, using experimental measurements and Monte Carlo simulation, confirmed that the time resolution in a PET scanner is dependent on the energy of the detected photon pair. Moreover, it was observed that trues, single and multiple scatter in general have different time distributions. The full width half maximum (FWHM) of the time distribution of trues and scatter in different configurations of phantoms and energy threshold were evaluated. The width of the time distribution for scatter was observed to be much larger than for trues, particularly because of the effect of multiple scatter, if low energy thresholds are used. On the other hand, the use of high energy thresholds (for example, 435 keV) reduces the time distribution FWHM of the overall scatter and the amount of multiple scatter accepted: in that case, the single scatter simulation provides a good estimate of the experimental scatter time distribution. Moreover, at these high thresholds, the time distribution of the scatter becomes very close to that of the trues, and even using the trues time resolution for the scatter simulation will not produce a significant effect on the final image. View full abstract»

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  • Multi-Level Time-Over-Threshold Method for Energy Resolving Multi-Channel Systems

    Page(s): 2545 - 2548
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (611 KB) |  | HTML iconHTML  

    Pixellated radiation detectors require an energy resolving multichannel system. The time-over-threshold (ToT) method provides an inexpensive way to energy-resolving signal processing. However, the conventional, single-threshold ToT method suffers from a small dynamic range and poor linearity. We have studied linearity in a ToT system for typical shaping filters and propose a new, multi-level, ToT scheme. This method provides higher linearity and wider dynamic range. We have analyzed the typical signal cases of triangular, CR-RC, and Semi-Gaussian filters, and achieved a linearity of less ≤3% in Integral Non-Linearity (INL). View full abstract»

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  • System Tradeoffs in Gamma-Ray Detection Utilizing SPAD Arrays and Scintillators

    Page(s): 2549 - 2557
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (611 KB) |  | HTML iconHTML  

    We present a statistical analysis of the tradeoffs between detector jitter and light detection efficiency for TOF PET gamma-ray detectors based on SPAD arrays and crystal scintillators. Results show that increasing the light detection probability is more important to improving the coincidence timing resolution than decreasing the detector jitter for modern scintillators. For a SPAD TDC array with a fill factor around 15% and a detector jitter of 120 ps, it is shown that a SiPM with a 30% fill factor and a jitter of 240 ps will produce a better timing resolution when using a LYSO crystal. Results also imply that SPAD TDC arrays might be competitive in TOF PET with SiPMs if faster scintillators are developed in the future and SPAD TDC arrays maintain a much lower jitter than SiPMs. View full abstract»

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  • GATE Simulations of Human and Small Animal PET for Determination of Scatter Fraction as a Function of Object Size

    Page(s): 2558 - 2563
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (649 KB) |  | HTML iconHTML  

    In 2D-mode positron emission tomography (PET), scatter is either compensated by approximate methods based on the existing emission data or ignored altogether as the magnitude of the scatter fraction (SF) is on the order of 10%-20%. In clinical PET studies, however, attenuation and sophisticated scatter correction methods are required along with CT or radionuclide transmission scans. With the growing interest in small animal imaging, these correction methods are being translated to small animal scanners, but there is little scientific information about the requirements associated with smaller size objects and scatter geometries. In this study, we focused on the magnitude of the scatter through a series of scatter fraction simulations. To determine the scatter as a function of object size, we performed Monte Carlo simulations using GATE (Geant4 application for emission tomography). Models of the ECAT HR+ PET scanner (included in the GATE package) and the Siemens Inveon small animal scanner (generated by the first author) were used. Simulations were performed for several digital phantoms including the NEMA, XCAT and MOBY phantoms over a wide range of sizes. Small animal NEMA-like phantoms indicated that for cylindrical objects less than 5 cm diameters (encompassing small rats and all mice), the scatter fraction was lower than 17.5% for the 350-650 keV and 20% for the 250-750 keV windows. Similar values were obtained for the MOBY phantoms for the respective sizes. On the other hand, the scatter fraction was more than 35% for even the smallest size human NEMA-like and XCAT phantoms. These results suggest that sophisticated scatter correction methods may not be required for the indicated sizes of mice and rats. View full abstract»

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Aims & Scope

IEEE Transactions on Nuclear Science focuses on all aspects of the theory and applications of nuclear science and engineering, including instrumentation for the detection and measurement of ionizing radiation; particle accelerators and their controls; nuclear medicine and its application; effects of radiation on materials, components, and systems; reactor instrumentation and controls; and measurement of radiation in space.

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