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Nuclear Science, IEEE Transactions on

Issue 1  Part 1 • Date Feb. 2004

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Displaying Results 1 - 25 of 41
  • [Front cover]

    Publication Year: 2004 , Page(s): c1
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    Freely Available from IEEE
  • IEEE Transactions on Nuclear Science publication information

    Publication Year: 2004 , Page(s): c2
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  • Table of contents

    Publication Year: 2004 , Page(s): 1 - 2
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  • Toward proton computed tomography

    Publication Year: 2004 , Page(s): 3 - 9
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    Proton therapy, long regarded as a superior method of radiation therapy, is now becoming more cost effective and is being used in a number of clinical centers around the world. In light of this development the use of the proton beam itself should be considered for the most accurate method of treatment planning. X-ray computed tomography (XCT), which is widely available, has been used for the treatment planning for proton therapy. The basic interactions of XCT in matter are fundamentally different than those of the protons. Thus, the resulting density map from XCT is only an approximation of the true density map for proton therapy. Progress in proton computed tomography (pCT) is presented in this work. The experimental requirements for pCT are examined, and data analysis and Monte Carlo simulations are used to estimate the feasibility of pCT as an imaging modality. View full abstract»

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  • Characterization of single and multiple scatter from matter and activity distributions outside the FOV in 3-D PET

    Publication Year: 2004 , Page(s): 10 - 15
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    Operation of PET in 3-D mode, without internal septa results in increased sensitivity but at the cost of increased scatter fraction. Significant amounts of scattered events in 3-D PET either originate from activity outside the FOV (OFOV) or scatter from matter outside the FOV, complicating scatter correction methods. We performed 3-D PET simulations with scanner geometry based on the GE Advance with several phantom geometries designed to characterize all scatter with particular attention to that from outside the FOV. Scatter from OFOV matter was deduced by performing simulations with matter and activity within the FOV only (short phantom). Studies were repeated with phantoms with identical characteristics inside the FOV but with additional OFOV material (long phantom) but no activity outside the FOV. The incremental effect of OFOV activity was then determined by repeating the long phantom studies with additional activity. Scatter was also classified as single or multiple. In summary, the data allow extraction of yields from unscattered and all types of scattered events. The effect of source position, both within and external to the FOV, on scatter was determined by performing a series of simulations with point sources and techniques similar to those described above. The effect of energy discriminator setting (with BGO detectors) was also studied and data sets were generated for five settings from 300 to 425 keV. Using a Zubal phantom with the lungs and heart in the FOV and the abdomen outside the FOV and with a 300 keV discriminator, we find a total scatter fraction of 57%. Of the total scatter, 7.4% comes from OFOV matter, and 24% from OFOV activity. If the discriminator is increased to 425 keV the scatter fraction drops to 36%. OFOV scatter, particularly from OFOV activity, becomes relatively less important with the OFOV matter contribution dropping to 5.3% and OFOV activity contribution to 17%. Additionally, the spatial distributions of scatter from external matter and external activity were found to be different. View full abstract»

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  • Component-based normalization for panel detector PET scanners

    Publication Year: 2004 , Page(s): 16 - 20
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    We present a component-based normalization method for a PET scanner with a rotating array of panel detectors. The normalization procedure is designed to robustly normalize sinograms acquired with different levels of scattered radiation and at different count rates, flattening the response and removing artifactual detector-block patterns, which if uncorrected could cause ring artifacts in images and intensity variations along the scanner axis. Coincidence events are binned during acquisition into a 3-D sinogram S(r,φ,z,seg) where r is radius, φ is angle, z is the axial position, and seg is the segment. In its simple form, the normalization N, defined by the equation S(normalized)=N*S(unnormalized), is assumed to take the angle-independent form N=1/(g(r,seg)*f(r,z,seg)*c(z,seg)), where the f term contains only low radial frequencies. The g and f terms are derived from a scan of a scatter-free uniform source. The c term, derived from a scan of a cylindrical phantom that scatters radiation and fills the axial field of view, removes high-frequency axial features in the sinogram but does not correct for the low-frequency scatter features which are handled by the reconstruction software. As the count rate changes, one finds that sinograms normalized by this simple procedure are afflicted by a high-frequency axial pattern due to a count rate dependent sensitivity change at the edges of blocks. This artifact is addressed by a multiplicative correction of the form γ=γ(S,z), where S is the singles counting rate and γ is a periodical function with the periodicity of the array of detector blocks. View full abstract»

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  • Performance evaluation of MMP-II:A second-generation small animal PET

    Publication Year: 2004 , Page(s): 21 - 26
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    We have completed construction of a second-generation, single-plane small animal PET instrument based on LSO detectors. The second-generation design addresses some of the limitations in the first-generation. The purpose of the work reported here was to characterize the physical performance of this instrument. Results of the performance measurements include: Spatial resolution=1.25 mm at field center and 1.5 mm at 2 cm radius; point source sensitivity=56 cps/uCi,; scatter fractions of 0.019 and 0.056 in 3.8 and 6 cm diameter cylinders respectively; linearity of reconstructed signal within 5% up to 100 uCi/cc and acceptable dead-time performance up to 25 k true cps. Examples of phantom and animal images are also presented. View full abstract»

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  • Impact of system design parameters on image figures of merit for a mouse PET scanner

    Publication Year: 2004 , Page(s): 27 - 33
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    In this study, an analytical simulation model was developed to investigate how system design parameters affect image figures of merit and task performance for small animal positron emission tomography (PET) scanners designed to image mice. For a very high resolution imaging system, important physical effects that may impact image quality are positron range, annihilation photon acollinearity, detector point-spread function (PSF) and coincident photon count levels (i.e., statistical noise). Modeling of these effects was included in an analytical simulation that generated multiple realizations of sinograms with varying levels of each effect. To evaluate image quality with respect to quantitation and detection task performance, four different figures of merit were measured: 1) root mean square error (RMSE); 2) a region of interest SNR (SNRROI); 3) nonprewhitening matched filter SNR (SNRNPW); and 4) recovery coefficient. The results indicate that for very high resolution imaging systems, the increase in positron range of C-11 compared to F-18 radiolabeling causes a significant reduction of quantitation (SNRROI) and detection (SNRNPW) accuracy for small regions. In addition, changing the shape of the detector PSF, which depends on crystal thickness, causes significant variations in quantitation and detection performance. However, while increasing noise levels significantly increase RMSE and decrease detectability (SNRNPW), the quantitation task performance (SNRROI), is less sensitive to noise levels. These results imply that resolution is more important than sensitivity for quantitation task performance, while sensitivity is a more significant issue for detection. The analytical simulation model can be used for estimating task performance of small animal PET systems more rapidly than existing full Monte Carlo methods, although Monte Carlo methods are needed to estimate system parameters. View full abstract»

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  • A comparison of planar versus volumetric numerical observers for detection task performance in whole-body PET imaging

    Publication Year: 2004 , Page(s): 34 - 40
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    The goal of this project is to determine if there is a difference between planar and volumetric numerical observers. The motivation comes from the use of a volumetric (3-D) display of image data (i.e., three orthogonal views through a volume image) to assess whole-body PET images in most, if not all, clinical PET centers. Studies of correlations between numerical observers and human observers (e.g., using receiver operating characteristic (ROC) detection analysis), however, typically use a planar (2-D) display and analysis methodology. In particular, planar implementations of the nonprewhitening matched filter (NPWMF) and the channelized Hotelling observer (CHO) have been extensively investigated as surrogates for measuring human detection task performance. To determine if there is a difference between planar and volumetric numerical observers, we analyzed the behavior of 2-D and 3-D implementations of the NPWMF and CHO numerical observers with multiple realizations of images with noise properties similar to those of whole-body PET oncology imaging. The results indicate that there is a significant increase in SNR or detectability of volumetric numerical observers relative to planar observers. This implies that volumetric and planar numerical observers may have different strengths of correlation with human observer performance, and that these correlations should be determined prior to using numerical observers to optimize algorithm or protocol performance for whole-body PET imaging. When axial smoothing is applied, however, to impose isotropic target resolution or to simulate fully 3-D PET data, the detectabilities of planar numerical observers are increased and the differences between planar and volumetric numerical observers become less significant. View full abstract»

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  • Count-rate dependent event mispositioning and NEC in PET

    Publication Year: 2004 , Page(s): 41 - 45
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    Most current PET detector designs suffer from event mispositioning at high count rates, as scintillation light from nearby and nearly simultaneous gamma ray conversions becomes mixed. We have used the NEMA NU 2-2001 70 cm test phantom and a Na-22 point source to quantify this effect as a function of activity on two block-detector tomographs (the Siemens/CTI HR+ and the General Electric Discovery LS), and two Anger-type PET tomographs (the Siemens ECAM DUET and the Philips CPET+). After accounting for event losses due to dead time, we find that the number of counts on LORs passing through a cylinder of diameter and height equal to the point-source full width at tenth-maximum measured at low rate surrounding the point source decreases by between 9% (HR+) and 35% (CPET+) at the activity giving rise to peak noise equivalent count (NEC) rate. Mispositioned events act to reduce signal-to-noise ratio, both by reducing apparent activity at the originating location and by increasing the signal background. We have reformulated the conventional expression for NEC rate to account for this phenomenon. The new formulation of NEC, which we call NEC*, results in a lower peak value which in turn occurs at a lower activity concentration than for the conventional formulation. View full abstract»

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  • PET-SORTEO: a Monte Carlo-based Simulator with high count rate capabilities

    Publication Year: 2004 , Page(s): 46 - 52
    Cited by:  Papers (40)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    Monte Carlo-based PET simulators are powerful tools for accurately generating projections of tracer distributions for given scanner specifications and attenuating media distributions. High activity-related phenomena, such as the randoms contribution as well as block and system deadtimes constitute a large source of artefact and must therefore be integrated within the simulation model along with the γ-ray interaction within the tissue or the scanner material. We present here the features of a Monte Carlo simulator, dedicated to full ring tomographs, which is able to generate scattered, unscattered, and randoms distributions from voxelized phantom descriptions, and which accounts for the data losses due to system deadtime. Simulations of the count rate performance of the ECAT Exact HR+ operating in 2-D and 3-D modes were found to be in good agreement with experimental measurements obtained for a wide range of activity levels and distributions. View full abstract»

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  • A positron-decay triggered transmission source for positron emission tomography

    Publication Year: 2004 , Page(s): 53 - 57
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    Attenuation of gamma rays is the most important correction required to provide artefact-free quantitative images in positron emission tomography (PET). We have tested a new technique, which allows multiple sources to be used for transmission scans. Each point source is surrounded by plastic scintillator, and the energy the positron must lose before annihilation is collected in the plastic scintillator coupled to a miniature photo-multiplier tube (PMT). The fast trigger from the PMT signals that positron decay has occurred, and arms a circuit to anticipate the arrival of one of the annihilation gamma rays in one of the scanner's conventional detectors. When this occurs, a line of response joining the current source position and detector position is identified. This technique has been tested using four 68Ge sources imbedded in 5 mm diameter plastic cylinders coupled to miniature PMTs on the "ANIPET" small animal PET scanner at the Montreal Neurological Institute. Cross-talk (one plastic scintillator recording a gamma ray from any adjacent source instead of a positron from its own source) was 0.5%, and the count rate in one channel was 198 kcps implying a positron detection efficiency of 44%. Finally, preliminary images were obtained of the feasibility of using positron-decay as a transmission source. View full abstract»

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  • Performance of a PET detector with a 256ch flat panel PS-PMT

    Publication Year: 2004 , Page(s): 58 - 62
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    A 256ch flat panel position sensitive photomultiplier tube (FP-PMT) is a promising device for a PET detector because of its large opening area, 52 mm × 52 mm, and small dead space. The useful area of the 256ch FP-PMT is 89% to the opening area. The 256ch FP-PMT contains 16 × 16 matrix anodes with 3.04 mm intervals between them so that the 256ch FP-PMT affords optical coupling with a 16 × 16 array of scintillation crystals having 3 mm × 3 mm bottom area. Its 14.7 mm thickness will also ensure a compact volume and less weight for the PET apparatus. Using a prototype 256ch FP-PMT, we measured light spread function of a central anode and crystal identification ability with 2.9 mm × 2.9 mm × 7.5 mm Gd2SiO5 (GSO) crystals. The full width at half maximum of the light spread function was found to be 4.6 mm. As regards positioning performance, the resultant positioning image map assures its capability for crystal identification in a 16 × 16 array of the GSO crystals. For the use of a 256ch FP-PMT having a large useful area, we made a new proposal for easier construction of an array with many crystal elements. The way utilizing multilayer polymer mirrors, a reflector, properly processed by laser can be applied to other various shaped detectors. View full abstract»

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  • Compact CT/SPECT small-animal imaging system

    Publication Year: 2004 , Page(s): 63 - 67
    Cited by:  Papers (26)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    We have developed a dual-modality CT/SPECT imaging system for small-animal imaging applications. The X-ray system comprises a commercially available micro-focus X-ray tube and a CCD-based X-ray camera. X-ray transmission measurements are performed based on cone-beam geometry. Individual projections are acquired by rotating the animal about a vertical axis in front of the CCD detector. A high-resolution CT image is obtained after reconstruction using an ordered subsets-expectation maximization (OS-EM) reconstruction algorithm. The SPECT system utilizes a compact semiconductor camera module previously developed in our group. The module is mounted perpendicular to the X-ray tube/CCD combination. It consists of a 64 × 64 pixellated CdZnTe detector and a parallel-hole tungsten collimator. The field of view is 1 square inch. Planar projections for SPECT reconstruction are obtained by rotating the animal in front of the detector. Gamma-ray and X-ray images are presented of phantoms and mice. Procedures for merging the anatomical and functional images are discussed. View full abstract»

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  • Phantom studies investigating extravascular density imaging for partial volume correction of 3-D PET 18FDG studies

    Publication Year: 2004 , Page(s): 68 - 71
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    Limited scanner resolution and cardiac motion contribute to partial volume (PV) averaging of cardiac PET images. An extravascular (EV) density image, created from the subtraction of a blood pool scan from a transmission image, has been used to correct for PV averaging in H215O studies using 2-D imaging but not with 3-D imaging of other tracers such as 18FDG. A cardiac phantom emulating the left ventricle was used to characterize the method for use in 3-D PET studies. Measurement of the average myocardial activity showed PV losses of 32% below the true activity (p<0.001). Initial application of the EV density correction still yielded a myocardial activity 13% below the true value (p<0.001). This failure of the EV density image was due to the 1.66 mm thick plastic barrier separating the myocardial and ventricular chambers within the phantom. Upon removal of this artifact by morphological dilation of the blood pool, the corrected myocardial value was within 2% of the true value (p=ns). Spherical ROIs (diameter of 2 to 10 mm), evenly distributed about the myocardium, were also used to calculate the average activity. The EV density image was able to account for PV averaging throughout the range of diameters to within a 5% accuracy, however, a small bias was seen as the size of the ROIs increased. This indicated a slight mismatch between the emission and transmission image resolutions, a result of the difference in data acquisitions (i.e., span and ring difference) and default smoothing. These results show that the use of EV density image to correct for PV averaging is possible with 3-D PET. A method of correcting barrier effects in phantoms has been presented, as well as a process for evaluating resolution mismatch. View full abstract»

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  • Validation and evaluation of model-based crosstalk compensation method in simultaneous 99mTc stress and 201Tl rest myocardial perfusion SPECT

    Publication Year: 2004 , Page(s): 72 - 79
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB) |  | HTML iconHTML  

    Simultaneous acquisition of 99mTc stress and 201Tl rest myocardial perfusion SPECT has several potential advantages, but the image quality is degraded by crosstalk between the Tc and Tl data. We have previously developed a crosstalk model that includes estimates of the downscatter and Pb X-ray for use in crosstalk compensation. In this work, we validated the model by comparing the crosstalk from 99mTc to the Tl window calculated using a combination of the SimSET-MCNP Monte Carlo simulation codes. We also evaluated the model-based crosstalk compensation method using both simulated data from the 3-D MCAT phantom and experimental data from a physical phantom with a myocardial defect. In these studies, the Tl distributions were reconstructed from crosstalk contaminated data without crosstalk compensation, with compensation using the model-based crosstalk estimate, and with compensation using the known true crosstalk, and were compared with the Tl distribution reconstructed from uncontaminated Tl data. Results show that the model gave good estimates of both the downscatter photons and Pb X-rays in the simultaneous dual-isotopes myocardial perfusion SPECT. The model-based compensation method provided image quality that was significantly improved as compared to no compensation and was very close to that from the separate acquisition. View full abstract»

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  • A study of intrinsic Crystal-pixel light-output spread for discrete scintigraphic imagers modeling

    Publication Year: 2004 , Page(s): 80 - 84
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    This paper is focused on the discrete scintillation imaging devices, consisting of crystal arrays and metal-channel dynode Hamamatsu 1" and 2" square position sensitive photomultiplier tubes (PSPMTs). These devices are suitable for nuclear medicine based high resolution applications, and, particularly, for single photon emission computed tomography (SPECT). The model of scintillation light distribution (SLD) previously developed was able to distinguish the responses from crystal-pixels with different side, but it was not detailed enough to explain the influence of crystal-thickness. For this reason the experimental data were reviewed to find a new and more adequate analytical model. The improved SLD model explains the influence both of crystal-side and crystal-thickness on the scintillation light-output spread. The SLD expression is quite simple and its spread depends only on one q-parameter. This expression is well adaptable over the range of examined crystal arrays. Furthermore, in the considered experiments, the SLD q-parameter was found linearly dependent on crystal-pixel shape factor S/V(S=blind-surfacearea,V=volume). An overview of discrete scintillation imager simulator (DISIS) computer code is reported. Major outcomes of this work are: 1) the improved expression of SLD, which consolidates the DISIS performances, and 2) a tool for local SLD-spread control in the imager field of view (FOV). View full abstract»

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  • Optimal calibration of PET Crystal position maps using Gaussian mixture models

    Publication Year: 2004 , Page(s): 85 - 90
    Cited by:  Papers (6)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    A method is developed for estimating optimal PET gamma-ray detector crystal position maps, for arbitrary crystal configurations, based on a binomial distribution model for scintillation photon arrival. The approach is based on maximum likelihood estimation of Gaussian mixture model parameters using crystal position histogram data, with determination of the position map taken from the posterior probability boundaries between mixtures. This leads to minimum probability of error crystal identification under the assumed model. View full abstract»

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  • Position sensitive APDs for small Animal PET imaging

    Publication Year: 2004 , Page(s): 91 - 95
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    In this paper, investigation of position sensitive avalanche photodiodes (PSAPDs) as optical detectors for reading out segmented scintillation arrays of LSO in high resolution PET modules is reported. PSAPDs with 8×8 mm2 and 14×14 mm2 area have been characterized with single LSO crystals and arrays. Energy resolution of 19% (FWHM) for 511 keV γ-rays and coincidence timing resolution of ∼3 ns (FWHM) have been recorded with PSAPD coupled to 1×1×20 mm3 LSO detectors. Flood histogram studies have been successfully conducted by coupling multi-element element LSO arrays (1 mm pixels, 20 mm tall) to the PSAPDs. Finally, depth of interaction (DOI) resolution of <4.5 mm (FWHM) has been measured by coupling two PSAPDs on opposite ends of a 20 mm long LSO crystal with a 1×1 mm2 cross section. Based on these results, PSAPDs appear to be promising for high resolution PET. An important advantage of these PSAPDs is significant reduction in electronic readout requirements. View full abstract»

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  • Bismuth tri-iodide polycrystalline films for digital X-ray radiography applications

    Publication Year: 2004 , Page(s): 96 - 100
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    Bismuth tri-iodide polycrystalline films were grown by the physical vapor deposition method. Glass 1''×1'' in size was used as the substrate. Palladium was deposited previously onto the substrates as the rear contact. For growth, bismuth tri-iodide 99.999% was heated at 130-170°C under high vacuum atmosphere (5×10-5 mmHg) or under Ar pressure for 20 hours. Film thickness was measured by the transmission of 59.5 keV 241Am emission, giving values ranging from 90 to 130 μm (5%). Film grain size was measured by scanning electron microscopy, and it gave an average of (50±20) μm. Detectors were made with the films by depositing palladium as the front contact (contact area 4 mm2) and then performing acrylic encapsulation. Resistivities of 6×1012 Ω.cm and current densities of 240 pA/cm2 at 20 V were obtained for these detectors. The electron mobility and lifetime and the electron mobility-lifetime product were measured by the transient charge technique, which gave values of 4.4 cm2/V.s, 3.3×10-7s and 1.4×10-6 cm2/V respectively. X-ray film response was checked by irradiating the films with a 241Am source and with an X-ray beam, for different beam energies and intensities and for several bias voltages applied to the detector. A linear response with exposure rate was obtained. Finally, the results were compared with previous ones for monocrystals of bismuth tri-iodide and polycrystalline films of alternative materials like lead iodide and mercuric iodide. View full abstract»

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  • Evaluation of maximum-likelihood position estimation with Poisson and Gaussian noise models in a small gamma camera

    Publication Year: 2004 , Page(s): 101 - 104
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    It has been reported that maximum-likelihood position estimation (MLPE) algorithms offer advantages of improved spatial resolution and linearity over conventional Anger algorithm in gamma cameras. While the fluctuation of photon measurements is more accurately described by Poisson than Gaussian distribution model, the likelihood function of a scintillation event assumed to be Gaussian could be more easily implemented and might provide more consistent outcomes than Poisson-based MLPE. The purpose of this study is to evaluate the performances of the noise models, Poisson and Gaussian, in MLPE for the localization of photons in a small gamma camera (SGC) using NaI(Tl) plate and PSPMT. The SGC consisted of a single NaI(Tl) crystal, 10 cm in diameter and 6 mm thick, optically coupled to a PSPMT (Hamamatsu R3292-07). The PSPMT was read out using a resistive charge divider, which multiplexes 28(X) by 28(Y) cross wire anodes into four channels. Poisson and Gaussian-based MLPE methods have been implemented using experimentally measured detector response functions (DRF). The averaged intrinsic spatial resolutions were 3.14, 3.09, and 2.88 mm, the integral uniformities were 15.3%, 12.3%, and 11.4%, and the averaged linearities were 0.75, 0.33, and 0.22 mm for Anger logic, Poisson, and Gaussian-based MLPE, respectively. MLPEs considerably improved linearity and uniformity compared to Anger logic. Gaussian-based MLPE, which is easy to implement, allowed to obtain better linearity and uniformity performances than the Poisson-based MLPE. View full abstract»

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  • Tuning tool for image quality optimization of a hybrid semiconductor pixel detector

    Publication Year: 2004 , Page(s): 105 - 109
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    Linear systems theory is used for the numerical assessment of the detective quantum efficiency (DQE) of the hybrid semiconductor pixel detector DIXI. The Monte Carlo based code GEANT is used to simulate the photon transport in the sensor, charge transport modeling is treated analytically and the readout chip is simulated using PSPICE. The DQE for two differently shaped X-ray spectra of the same quality and for different operational conditions of the readout chip regarding the discrimination level are computed in order to validate the model. The model described in this paper can be adopted for optimizing the detector. View full abstract»

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  • Feasibility of a beta-gamma digital imaging probe for radioguided surgery

    Publication Year: 2004 , Page(s): 110 - 116
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB) |  | HTML iconHTML  

    We report here on a novel design of a digital, intraoperative imaging probe intended for use in radio-guided surgical procedures in conjunction with radiolabels such as 131I and 18F. The probe allows the user to rapidly localize tumors by detecting the highly penetrating gamma rays, and then image the tumor with the short-range beta rays. The system provides a rapid, high-resolution, image of the interrogated area, fulfilling the need for clear delineation of tumors during radio-guided surgical procedures. The beta imaging sensor consists of a microcolumnar CsI(Tl) scintillator screen capable of providing very high detection efficiency, high light output and excellent spatial resolution coupled to a CCD via a flexible, coherent fiberoptic bundle. The gamma sensor is a shielded piece of crystalline CsI(Tl) coupled to a photodiode located behind the image sensitive front end. The feasibility of this design was studied by separately testing the beta imaging and gamma detection components. The operation of the components was characterized with intrinsic performance measurements of count rates, signal-to-noise ratios, spatial resolution, as well as time for acquiring useful images using radionuclide and anthropomorphic phantoms. View full abstract»

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  • A dual surface barrier detector unit for beta-sensitive endoscopic probes

    Publication Year: 2004 , Page(s): 117 - 122
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    The excellent targeting of positron-emitting radiopharmaceuticals such as 18F-Fluorodeoxyglucose (FDG) to cancer has inspired the development of a number of handheld beta probes to assist in surgeries. The use of these devices could potentially be expanded to utilization in minimally invasive techniques such as endoscopy. In this work, we describe the development and initial testing of a miniature beta-sensitive detector unit suitable for use in minimally invasive procedures. The detector consisted of two surface barrier detectors (active area=3 mm diameter and depletion layer depth=0.5 mm) mounted back-to-back in a PC board frame. This geometry allowed the rear detector to be shielded from the beta flux striking the front detector (most photons passed through the detector) so that its signal could be used to correct for photon contamination of the beta flux detected by the front detector. Initial testing of the system included measurement of the beta and photon detection sensitivities (1.87±0.02 cps/nCi (0.05±5.4×10-4 cps/Bq) and 1.2×10-4±9×10-5 cps/nCi (3.24×10-6±2.4×10-6 cps/Bq), respectively) and mapping of the two-dimensional point spread function. The spatial resolution of the system is 3.05 mm FWHM. The potential effectiveness of the detector in clinical use was investigated by surveying a simulated esophagus containing radiotracer-avid areas of cancer. The results from this test demonstrated the ability of the detection system to distinguish focal areas of increased FDG uptake from surrounding normal tissue in a realistic annihilation photon flux environment. These encouraging results indicate that this detector unit is suitable for incorporation into a new beta-sensitive endoscopic probe system currently under development. View full abstract»

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  • Wavelet crosstalk matrix and its application to assessment of shift-variant imaging systems

    Publication Year: 2004 , Page(s): 123 - 129
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB) |  | HTML iconHTML  

    The objective assessment of image quality is essential for design of imaging systems. Barrett and Gifford introduced the Fourier crosstalk matrix and use it to analyze cone-beam tomography. Fourier crosstalk matrix is a powerful technique for discrete imaging systems that are close to shift invariant because it is diagonal for continuous linear shift-invariant imaging systems. However, for a system that is intrinsically shift-variant, Fourier techniques are not particularly effective. Since Fourier bases have no spatial localization property, the shift-variance of the imaging system cannot be shown by the response of individual Fourier bases; rather, it is shown in the correlation between the Fourier coefficients. This makes the analysis and optimization quite difficult. In this paper, we introduce a wavelet crosstalk matrix based on wavelet series expansions. The wavelet crosstalk matrix allows simultaneous study of the imaging system in both the frequency and spatial domains. Hence, it is well suited for shift-variant systems. We compared the wavelet crosstalk matrix with the Fourier crosstalk matrix for several simulated imaging systems, namely the interior and exterior tomography problems, a dual-planar positron emission tomograph, and a rectangular geometry positron emission tomograph. The results demonstrate the advantages of the wavelet crosstalk matrix in analyzing shift-variant imaging systems. View full abstract»

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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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