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Nuclear Science, IEEE Transactions on

Issue 5 • Date Oct. 2002

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Displaying Results 1 - 25 of 58
  • Nuclear Medical and Imaging Sciences (NMIS)

    Page(s): 2041 - 2046
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    Freely Available from IEEE
  • Regularized iterative reconstruction in tensor tomography using gradient constraints

    Page(s): 2387 - 2393
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1687 KB) |  | HTML iconHTML  

    This paper investigates the iterative reconstruction of tensor fields in diffusion tensor magnetic resonance imaging (MRI). The gradient constraints on eigenvalue and tensor component images of the diffusion tensor were exploited. A computer-generated phantom was used in order to simulate the diffusion tensor in a cardiac MRI study with a diffusion model that depends on the fiber structure of the myocardium. Computer simulations verify that the regularized methods provide an improved reconstruction of the tensor principal directions. The reconstruction from experimentally acquired data is also presented. View full abstract»

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  • Comparison of scatter compensation strategies for myocardial perfusion imaging using Tc-99m labeled sestamibi

    Page(s): 2309 - 2314
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    Scatter can be a confounding problem in the detection of perfusion defects in myocardial perfusion imaging. The goal of this investigation was to compare practical methods of scatter compensation representing different classes of compensation strategies. The methods investigated were: (1) modification of the energy window; (2) use of effective values of attenuation coefficients; (3) estimating the scatter distribution from energy spectrum information; and (4) estimating the scatter distribution in the spatial domain using the attenuation maps and scatter kernels. Monte Carlo simulated projections from two MCAT source distributions were used to investigate the impact of the various methods on residual scatter and myocardial uniformity. The investigation showed that each of the methods reduce the scatter significantly; however, the spatial domain method gave the least variation with the different source distributions and the best uniformity. View full abstract»

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  • A compact 16-module camera using 64-pixel CsI(Tl)/Si p-i-n photodiode imaging modules

    Page(s): 2228 - 2235
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    We present a compact, configurable scintillation camera employing a maximum of 16 individual 64-pixel imaging modules resulting in a 1024-pixel camera covering an area of 9.6 cm×9.6 cm. The 64-pixel imaging module consists of optically isolated 3 mm×3 mm×5 mm CsI(Tl) crystals coupled to a custom array of Si p-i-n photodiodes read out by a custom integrated circuit (IC). Each imaging module plugs into a readout motherboard that controls the modules and interfaces with a data acquisition card inside a computer. For a given event, the motherboard employs a custom winner-take-all IC to identify the module with the largest analog output and to enable the output address bits of the corresponding module's readout IC. These address bits identify the "winner" pixel within the "winner" module. The peak of the largest analog signal is found and held using a peak detect circuit, after which it is acquired by an analog-to-digital converter on the data acquisition card. The camera is currently operated with four imaging modules in order to characterize its performance. At room temperature, the camera demonstrates an average energy resolution of 13.4% full-width at half-maximum (FWHM) for the 140-keV emissions of 99mTc. The system spatial resolution is measured using a capillary tube with an inner diameter of 0.7 mm and located 10 cm from the face of the collimator. Images of the line source in air exhibit average system spatial resolutions of 8.7- and 11.2-mm FWHM when using an all-purpose and high-sensitivity parallel hexagonal holes collimator, respectively. These values do not change significantly when an acrylic scattering block is placed between the line source and the camera. View full abstract»

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  • MicroPET imaging with nonconventional isotopes

    Page(s): 2119 - 2126
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    The utilization of new positron emitting isotopes for position emission tomography (PET) imaging raises several questions about their ability to provide images of good quality and to perform accurate quantification. This issue is even more pertinent when using high-resolution scanners designed for the imaging of small animals. At Washington University, we are currently producing a whole array of positron emitters; some of them, like Ga-66 and Br-76, emit high-energy positrons and prompt gamma rays that affect spatial resolution and increase the random coincidence contribution. We have now started to evaluate these isotopes in terms of their ability to perform high-quality imaging. Spatial resolution measurements were evaluated using the Concorde MicroSystem Inc. microPET-R4 camera. Electron transport calculations have been performed and compared with experimental data. They revealed that for this camera, the detector size is still the limiting factor on resolution for isotopes emitting low-energy positrons like F-18 and Cu-64. The transaxial resolution was measured to be around 2 mm at the center of the field of view (FOV) for these isotopes. The dominant factor becomes the positron range for other isotopes like Cu-60 and Tc-94 m, with transaxial resolution of 3.5 and 4.3 mm, respectively. Due to the long tail of the positron range distribution; a strong contrast reduction is observed. In this paper, experimental data on spatial resolution will be presented for a number of nonconventional PET isotopes, and consequences on image quality will be discussed. View full abstract»

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  • Medipix2: A 64-k pixel readout chip with 55-μm square elements working in single photon counting mode

    Page(s): 2279 - 2283
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    The Medipix2 chip is a pixel-detector readout chip consisting of 256 × 256 identical elements, each working in single photon counting mode for positive or negative input charge signals. Each pixel cell contains around 500 transistors and occupies a total surface area of 55 μm × 55 μm. A 20-μm wide octagonal opening connects the detector and the preamplifier input via bump bonding. The preamplifier feedback provides compensation for detector leakage current on a pixel by pixel basis. Two identical pulse height discriminators are used to create a pulse if the preamplifier output falls within a defined energy window. These digital pulses are then counted with a 13-b pseudorandom counter. The counter logic, based in a shift register, also behaves as the input-output register for the pixel. Each cell also has an 8-b configuration register which allows masking, test-enabling and 3-b individual threshold adjust for each discriminator. The chip can be configured in serial mode and readout either serially or in parallel. The chip is designed and manufactured in a 6-metal 0.25-μm CMOS technology. First measurements show an electronic pixel noise of 140 e~ root mean square (rms) and an unadjusted threshold variation around 360 e~ rms. View full abstract»

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  • Development of a daily quality check procedure for the High-Resolution Research Tomograph (HRRT) using natural LSO background radioactivity

    Page(s): 2074 - 2078
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    A daily quality check plays an important role for clinical medical systems like a positron emission tomograph (PET). To guarantee image quality a constant monitoring of the scanner integrity is essential. On present PET scanners, the built-in transmission sources are being used for the measurement of a uniform blank scan and the computation of detector-block efficiencies. These efficiencies can be compared to reference data and deviations indicate changes of the scanner condition. On the High-Resolution Research Tomograph (ECAT HRRT) the design of the transmission source makes this method impractical. For that reason we investigated the use of the natural background radioactivity from the new scintillator material LSO as a uniform source. A procedure was developed to measure detector-block sensitivities and energy spectra directly. An initial quality check scan is the basis for comparison of daily scans, so that gain shifts of photomultipliers and specific hardware defects can be detected. With an improved list mode based data acquisition it was possible to reduce the acquisition time to around 3 h despite the low LSO count rate, so that this routine is as practical as previous procedures in clinical routine. View full abstract»

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  • Performance evaluation of A-SPECT: a high resolution desktop pinhole SPECT system for imaging small animals

    Page(s): 2139 - 2147
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    Pinhole collimation of gamma rays to image distributions of radiolabeled tracers is considered promising for use in small animal imaging. The recent availability of transgenic mice, coupled with the development of 125I and 99mTc labeled tracers, has allowed the study of a range of human disease models while creating demand for ultrahigh resolution imaging devices. We have developed a compact gamma camera that, in combination with pinhole collimation, allows for accessible, ultrahigh resolution in vivo single photon emission computed tomography (SPECT) imaging of small animals. The system is based on a pixilated array of NaI(Tl) crystals coupled to an array of position sensitive photomultiplier tubes. Interchangeable tungsten pinholes with diameters ranging from 0.5 to 3 mm are available, allowing the camera to be optimized for a variety of imaging situations. We use a three dimensional maximum likelihood expectation maximization algorithm to reconstruct the images. Our evaluation indicates that high quality, submillimeter spatial resolution images can be achieved in living mice. Reconstructed axial spatial resolution was measured to be 0.53, 0.74, and 0.96 mm full width at half maximum (FWHM) for rotation radii of 1, 2, and 3 cm, respectively, using the 0.5-mm pinhole. In this configuration, sensitivity is comparable to that of a high-resolution parallel hole collimator. SPECT images of hot- and cold-rod phantoms and a highly structured monkey brain phantom illustrate that high quality images can be obtained with the system. Images of living mice demonstrate the ability of the system to obtain high-resolution images in vivo. The effect of object size on the quantitative assessment of isotope distributions in an image was also studied. View full abstract»

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  • A study of scintillation beta microprobes

    Page(s): 2208 - 2212
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    Several types of scintillation microprobes have recently been developed to directly measure positron activity from radiotracers in live animals. These probes consist of either a small lutetium oxyorthosilicate (LSO) crystal or plastic scintillator coupled to an optical fiber that is read out with a photomultiplier tube operated in a single photon counting mode. In this paper, a comparison is made between the two types of probes in terms of their sensitivity to both positrons and gammas. It was found that LSO offers very high sensitivity to positrons due to its high density and light output, and allows the construction of very small probes for certain applications. The LSO probe can also provide effective discrimination between positrons and gammas, and provide better localization of positron decays, using pulse height discrimination. Results are also given on the use of the microprobe on live laboratory animals. View full abstract»

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  • Optimization of iterative reconstructions of 99mTc cardiac SPECT studies using numerical observers

    Page(s): 2355 - 2360
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    In this paper, we investigate the use of a numerical observer to optimize ordered-subset expectation maximization (OSEM) reconstructions for the detection of coronary artery disease (CAD). The parameters optimized were the iteration number and the full-width at half-maximum of three-dimensional Gaussian postfiltering. The numerical observer employed in the optimization was the channelized Hotelling observer (CHO). The CHO had been used previously to rank tumor detection accuracy for different reconstruction strategies in Ga-67 images, showing good agreement with the rankings of human observers. The intent of this paper was to determine if this CHO could also be employed for the detection of CAD. Results indicate that when grayscale (quantized) images are used, the CHO optimization results correlate well with human observers. On the other hand, when the CHO was used with floating-point images, it provided very good detection performance even when the images were excessively filtered. This result was at odds with the human-observer performance which showed a decrease in detection accuracy with highly smoothed images. This reflects the need to better model the detection task of the human observers who usually view and rank grayscale images and by appropriately modeling the image noise that quantization introduces, we show that the CHO can better match human-observer detection performance. View full abstract»

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  • Diode-type CdTe strip and linear array detectors for gamma-ray detection and imaging

    Page(s): 2250 - 2255
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    Diode-type CdTe detectors were fabricated in two different approaches for gamma-ray detection and imaging applications. The first type is a monolithic one-dimensional (1-D) detector with segmented n-type strips formed on the p-like CdTe crystal wafer. N-type strips were formed by diffusing indium using an excimer laser annealing process. In another approach, single element diode-type detectors were fabricated by growing an iodine-doped epitaxial layer on the p-like CdTe crystal in a metalorganic chemical vapor deposition system working at a low substrate temperature. A 1-D linear array detector was then developed by mounting a number of such small element detectors in a row. Both types of detectors exhibited good diode-like property with suppressed leakage currents in the reverse bias direction, which enabled us to apply a high electric field on the detectors in order to improve their performance. Nuclear detection tests performed at room temperature using 57Co and 241Am radioisotopes showed improved and uniform spectral responses from both types of detectors. Details about the detector fabrication and the spectral results that demonstrate the imaging and spectroscopy capabilities of these detectors are presented. View full abstract»

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  • Gamma camera PET with low energy collimators: characterization and correction of scatter

    Page(s): 2067 - 2073
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    Imaging of myocardial viability with fluorodeoxyglucose (FDG) is possible with positron emission tomography (PET) and with SPECT. The image resolution from SPECT is poor but the data is reported to provide clinical information comparable to PET. Studies have just begun to appear using gamma camera PET and either axial slat collimators or open frame graded absorbers to image myocardial viability. Alternatively, it may be possible to use standard low energy collimators en detecting coincidences. Although image quality may suffer, it may be possible to devise methods such that no clinical information is lost. Such an approach also paves the way for dual isotope sequential or simultaneous imaging of coincidence and single photons. Here, we characterize the scatter fraction and scatter distribution of gamma camera PET with low energy collimators, and investigate the improvements possible with a convolution-subtraction scatter correction scheme. Monte Carlo simulations, line sources, a realistic phantom, and a human study were used. The scatter fraction was found to be almost identical to that obtained with axial slat collimators on a triple head gamma camera hybrid PET scanner. Images acquired with low energy collimators were degraded but still of good quality compared to acquisitions using axial collimation. The scatter correction scheme showed a degree of improvement over reconstructions without scatter correction. This approach is useful not only toward making sequential or simultaneous dual isotope imaging possible, but may also be useful to save time in a busy clinic that does both SPECT scans and cardiac FDG studies, since collimators would not need to be changed. View full abstract»

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  • Comparative study on the radiation damage of a-Si:H p-i-n diodes made by PECVD and ion shower doping

    Page(s): 2244 - 2249
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    Flat-panel detectors using amorphous silicon p-i-n diodes have been developed for chest and therapeutic portal imaging. In radiation therapy, an imaging device is exposed to a high radiation dose. The radiation damage affects the leakage current of diode and may decrease the whole system performance. In this research, we have investigated the radiation damage to the leakage current of a-Si:H diode made by plasma-enhanced chemical vapor deposition (PECVD) and ion-shower doping method, and studied the effect of a copper plate generally used in portal imaging to increase the efficiency of detector. We measured the transient current of diodes between radiation exposures, and obtained the leakage current of diodes as a function of absorbed dose. The two diodes show similar behavior when used with a copper plate. The leakage current shows a linear dependence on the absorbed dose, and threshold dose was observed when a copper plate was placed on the top. The ion-shower diode shows higher rate of current increase, which is considered to originate from the intrinsic junction properties. View full abstract»

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  • Septa design study for volumetric imaging in positron emission tomography

    Page(s): 2097 - 2102
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    Positron emission tomography (PET) has become an essential imaging tool to localize tumors in diagnostic radiology and to monitor the size of a lesion before and during the treatment in oncology. Currently, commercial PET cameras operate only in two extreme modes: i) no-septa: three-dimensional (3-D) acquisition mode, also called volumetric imaging; and ii) all-septa-in: two-dimensional (2-D) acquisition mode, also called multislice imaging. In this paper, intermediate septa designs in the brain mode have been sought to minimize the scatter and accidental coincidences with acceptable sensitivity loss. To achieve this goal, Monte Carlo simulations were performed to evaluate possible septa designs. Information about septal penetration, absorption and scattering components from simulations guided us to modify the thickness and total number of septa in the new configurations. Count rate performances of three septa configurations were measured on our experimental high resolution PET camera with 3.85-cm axial field-of-view (AFOV); the measurements were compared with the simulation results. No-septa configuration had lower noise equivalent count (NEC) compared the other two configurations because of small AFOV Monte Carlo simulations were performed to predict the count rate performances of seven septa configurations for 13.1-cm AFOV. In the large AFOV, because of increased number of line of responses, NEC rate for no-septa case peaked rapidly at 0.07 μCi/cc. No-septa configuration is not recommended for high count rate studies. In this case where activity density is 0.3 μCi/cc or more, 10-septa and 15-septa configurations performed better than the other configurations. Intermediate 5-septa designs with variable septum length performed better between 0.07-μCi/cc and 0.3-μCi/cc range which represents the clinical activity level for 18F-FDG brain studies. View full abstract»

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  • Iterative reconstruction of SPECT data with adaptive regularization

    Page(s): 2350 - 2354
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    A nonlinear regularizing least-square reconstruction criterion is proposed for simultaneously estimating a single-photon emission computed tomography (SPECT) emission distribution corrected for attenuation together with its degree of regularization. Only a regularization trend has to be defined and tuned once for all on a reference study. Given this regularization trend, the precise regularization weight, which is usually fixed a priori, is automatically computed for each data set to adapt to the noise content of the data. We demonstrate that this adaptive process yields better results when the noise conditions change than when the regularization weight is kept constant. This adaptation is illustrated on simulated cardiac data for noise variations due to changes in the acquisition duration, background intensity, and attenuation map. View full abstract»

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  • Count rate analysis of PET scanner designs based on a GSO depth of interaction detector with a large-area PS-PMT

    Page(s): 2218 - 2222
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    We have estimated count rate properties of three-dimensional (3-D) positron emission tomography (PET) scanners based on a Gd2SiO5:Ce (GSO) detector with depth of interaction (DOI) capability using a large-area position-sensitive photomultiplier tube (PS-PMT). The proposed detector unit consists of 64 crystal blocks with four stages of 2×2 GSO arrays coupled to a 52-mm square PS-PMT which has small dead space. With appropriate light control in the crystal block, DOI information can be obtained using simple Anger-type positioning logic. Thus, dead-time factors can be calculated using a count rate model with standard acquisition architecture. Compton and photoelectric interactions in the scintillator and uniform cylindrical phantoms were tracked by Monte Carlo simulation programs. Since the DOI detector can provide high resolution throughout the entire field of view, 3-D PET scanners with a large solid angle covered by the detectors with relatively small ring diameters were simulated. The preliminary results suggest that, compared to current PET scanners, high noise equivalent count rate can be obtained by the proposed scanner designs despite the relatively large size of the detector module. The count rate performance can be improved by the reduction of single events that cause block dead-time losses at the cost of a slight decrease in sensitivity. View full abstract»

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  • Optimization of septal spacing in hybrid PET using estimation task performance

    Page(s): 2127 - 2132
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    Hybrid PET imaging, a low cost alternative to dedicated PET, is now commonly used in many clinics. The major factors that limit image quality of hybrid positron emission tomography (PET) systems are a limited count-rate capability, and a low coincidence fraction (i.e., trues to singles ratio). Axial collimation or slats are typically used to reduce single (unpaired) photons from impinging on the detector face. Unfortunately, axial collimation also prevents a number of true coincidences from being detected. In this study, we have used a multi-parameter estimation task to study quantitation performance resulting from projection data obtained using a triple-head system with different levels of axial collimator septal spacing. Specifically, the task is the estimation of amplitude (A) and size (R) of a three-dimensional Gaussian function embedded in a uniform cylindrical background. To evaluate task performance, the bias and variance of maximum-likelihood estimates of the parameters are studied by forming an approximate joint probability density function for the estimates. It was observed that as projection data noise increases; joint PDFs of the estimates become more skewed, with a larger difference between the variance of estimates and their minimum variance bound (Cramer-Rao bound). Estimator performance varied as a function of lesion location, which was expected since coincidence sensitivity for rotating hybrid PET systems with axial collimation is position dependent. In general, results showed that approximately 2.0-cm septal spacing provided projection data with the best overall estimator performance for lesions located within the central 20-cm axial field-of-view. View full abstract»

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  • Real time β-imaging with silicon hybrid pixel detectors: kinetic measurements with C-14 amino acids and P-32 nucleotides

    Page(s): 2213 - 2217
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    We present some additional results obtained with the BETAview system, a digital system for real time β-imaging based on semiconductor pixel detectors and on a single photon counting read-out chip. We describe the system assembled with a Si detector, 300-μm thick, segmented into 64 ×64 square pixels with 170-μm pitch. The solid-state pixel array detector is bump-bonded pixel by pixel to a low threshold, single particle counting electronics, the photon counting chip (PCC) developed by the Medipix1 Collaboration for biomedical applications. Each cell (corresponding to a detector pixel) of the front-end chip has a maximum count rate of 2 MHz, a minimum nominal threshold of 1400 e- (corresponding about 5 keV in Si), and contains a 15-bit counter. The detector sensitive area is about 1 cm2, but several detectors could be assembled in arrays. The measured background counts were about 3.5×10-2 cps/cm2, which implies a very high sensitivity of the device. The detection threshold used in this experiment was ∼15 keV. We show the results obtained in the real-time monitoring of two biological dynamic processes: an amino acid uptake by living cells and the thermal denaturation process of oligonucleotides. Specifically, we have followed over time the accumulation of a marked amino acid ([14C]L-Leucine) into Octopus vulgaris eggs cells. The results, described in Section III-B, show that after about 20 min from the beginning of the uptake process, the radioactively marked eggs become clearly visible over the background culture radioactive medium. In Sections III-C and III-D, we also describe the successful performance of the β-imaging system in genetic studies involving the real time reconstruction of denaturation and kinetics curves for two different 32P-radiolabeled nucleotides. View full abstract»

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  • An adapted fan volume sampling scheme for 3-D algebraic reconstruction in linear tomosynthesis

    Page(s): 2366 - 2372
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    We study the reconstruction process when the X-ray source translates along a finite straight line, the detector moving or not. This process, called linear tomosynthesis, induces a limited angle of view, which causes the vertical spatial resolution to be poor. To improve this resolution, we use iterative algebraic reconstruction methods, which are commonly used for tomographic reconstruction from a reduced number of projections. With noisy projections, such algorithms produce poor quality reconstructions. To prevent this, we use a first object prior knowledge, consisting of piecewise smoothness constraint. To reduce the computation time associated with both reconstruction and regularization processes, we introduce a second geometrical prior knowledge, based on the linear trajectory of the X-ray source. This linear source trajectory allows us to reconstruct a series of two-dimensional (2-D) planes in a fan organization of the volume. Using this adapted fan volume sampling scheme, we reduce the computation time by transforming the initial three-dimensional (3-D) problem into a series of 2-D problems. Obviously, the algorithm becomes directly parallelizable. Focusing on a particular region of interest becomes easier too. The regularization process can easily be implemented with this scheme. We test the algorithm using experimental projections. The quality of the reconstructed object is conserved, while the computation time is considerably reduced, even without any parallelization of the algorithm. View full abstract»

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  • Comparison of rectangular and dual-planar positron emission mammography scanners

    Page(s): 2089 - 2096
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    Breast imaging using dedicated positron emission tomography (PEM) has gained much interest in the medical imaging field. In this paper, we compare the performance between a rectangular geometry and a parallel dual-planar geometry. Both geometries are studied with depth of interaction (DOI) detectors and non-DOI detectors. We compare the Fisher-information matrix, lesion detection, and quantitation of the four systems. The lesion detectability is measured by the signal-to-noise ratio (SNR) of a prewhitening numerical observer for detecting a known hot spot on a uniform background. Results show that the rectangular system with DOI has the highest SNR for the detection task and the lowest bias at any given noise level for the quantitation task. They also show that for small simulated lesions the parallel dual-planar system with DOI detectors outperforms the rectangular system with non-DOI detectors, while the rectangular system with non-DOI detectors can outperform the parallel dual-planar system with DOI detectors for large simulated lesions. View full abstract»

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  • An evaluation of the effect of filtering in 3-D OSEM reconstruction by using data from a high-resolution PET scanner

    Page(s): 2381 - 2386
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    We evaluated the effect of filtering in the three-dimensional (3-D) ordered subset expectation maximization (OSEM) algorithm for reconstruction of projection data obtained with a high-resolution 3-D positron emission tomography (PET) scanner. For this study, we used the inter-update Metz filtered OSEM (IMF-OSEM) algorithm, which was developed by the PARAPET project. IMF-OSEM is an implementation of the OSEM algorithm with some additional capabilities such as inter-update filtering. The projection data were acquired using the high-resolution PET camera developed at the University of Texas M. D. Anderson Cancer Center (MDAPET). This prototype camera, which is a multiring scanner without any septa, has a transaxial resolution of 2.8 mm, which allows better evaluation of the algorithm. We scanned three phantoms: a cylindrical uniform phantom, a cylindrical phantom containing four small lesion phantoms, and the Hoffman brain phantom. The effect of inter-filtering in OSEM reconstruction was evaluated by computing the noise level of the reconstructed images of the uniform phantom, studying the contrast recovery for the hot lesions in a warm background, and visually inspecting images especially those of the Hoffman brain phantom. In addition, the effect of post-filtering on the reconstructed images was evaluated. For the high statistics data, a good compromise between contrast recovery and noise level was achieved using 20-50 iterations for the plain OSEM algorithm. By visually inspecting the images of the Hoffman brain phantom and hot lesions, we observed that the plain OSEM algorithm, especially when followed by post-filtering, and the inter-update filtering with Metz power of 1 could reasonably reproduce the phantom's structure. We also found that inter-update filtering has the potential to produce a noise level and contrast recovery comparable with that using the plain OSEM algorithm at a lower iteration number; however, it also has a greater tendency to develop noise artifacts. View full abstract»

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  • A channelized-hotelling-trace collimator design method based on reconstruction rather than projections

    Page(s): 2155 - 2158
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    In this paper, a new single-photon emission-computed tomography (SPECT) collimator design technique is investigated. In this feasibility study, the collimator hole diameter is the only design variable changed. Other collimator parameters are fixed to a low-energy-high-resolution (LEHR) design. The design is based on a task of imaging a small hot lesion with a uniform background. A channelized hotelling trace is used to quantify the lesion detectability in a reconstructed image for a particular collimator parameter. The unique feature of this development is that the image quality is not evaluated for planar projection data, but rather is evaluated for the reconstructed tomographic image with an ordered-subset expectation-maximization reconstruction algorithm. Our results suggest that a collimator hole size that is larger than the LEHR collimator hole size is preferable for lesion detection. In SPECT, the optimal collimator design should be reconstruction algorithm dependent. View full abstract»

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  • Correction of the respiratory motion of the heart by tracking of the center of mass of thresholded projections: a simulation study using the dynamic MCAT phantom

    Page(s): 2159 - 2166
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    During normal breathing, heart motion is about 15 mm along the body axis in humans. We propose a method to track and to correct this motion after a list-mode acquisition which involves the recording of a signal proportional to respiratory volume. We use the dynamic MCAT (DMCAT) chest phantom to simulate 24 temporal frames regularly spaced during the respiratory cycle, for 60 projection angles over 360°. A 15-mm respiratory translation motion is simulated for the heart, liver and spleen. Thresholding of projections is used to reduce the influence of static activity on calculation of the axial center-of-mass (aCOM). Variation in the impact of attenuation as a function of projections and noise in the low-count projections rebinned from list-mode acquisitions is seen to limit ones ability to track respiratory motion using the aCOM. By including the recording of a signal proportional to the relative respiratory volume with the list-mode acquisition counts from different respiratory cycles can be combined to produce projections with common respiratory volumes. We have determined that the aCOMs determined from summing these common-volume based projections over the anterior to left-anterior oblique projection angles can be used to track respiratory motion as a function of the volume signal. Using this information on the variation of the aCOM as a function of the volume signal, the entire list-mode acquisition can then be rebinned into a projection set which is corrected for respiratory motion. After motion tracking, the mean absolute difference between the true motion curve and the aCOM curve is 0.10 cm for noisy studies. After correction no heart motion is visible on a cine display of projections. The polar map of myocardial MIBI uptake after motion correction is closer to that obtained when no respiratory motion is present than without correction. View full abstract»

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  • Scintillating fiber dosimeter for radiation therapy accelerator

    Page(s): 2223 - 2227
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB) |  | HTML iconHTML  

    Radiation therapy accelerators require highly accurate dose deposition and the output must be monitored frequently and regularly. Ionization chambers are the primary tool for this control, but their size and fragility make them unsuitable for use during patient treatment. In collaboration with a French center for cancer treatment in Caen, we describe the development and testing of a low-cost radiotherapy dosimeter (SDM) based on scintillating fibers and signal processing to reduce the effect of Cerenkov radiation background. The employment of photodiodes for light collection reduces the cost relative to systems using photomultipliers (PMTs). However, we have also developed a highly sensitive system that uses PMTs for very low-dose deposition for Brachytherapy. Comparison with standard ionization chambers shows about a 1% difference over a range of 6- to 25-MV photons. This dosimeter is 1 mm in diameter and can be placed where ever required including inside the body. Its small size and flexibility make it useful for delimiting critical regions, where organs may be very radiation sensitive. View full abstract»

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  • Comparison between a germanium orthogonal strip detector and an Anger camera through a simulation and modeling study

    Page(s): 2196 - 2202
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB) |  | HTML iconHTML  

    Progress in detector technology has led to the development of a new generation of pixel-based imaging devices as potential competitors for Anger-type scintillation cameras. We modeled a 11-mm-thick germanium orthogonal strip detector (GOSD) with 2-mm pitch and compared its performance to an Anger camera with a 10-mm-thick NaI(Tl) crystal. The Anger camera simulation method was validated by experimental measurements made with point and volume sources. Resolution and sensitivity were determined for air and scatter measurements. The device is intended for use in breast tumor imaging, and its expected performance was simulated in response to 5-, 7.5-, and 10-mm spherical tumors embedded in a previously reported phantom geometry used for the simulation of a CsI pixellated detector. Thorax, breast, and heart background contributions are considered in this phantom. A comparison of the results obtained indicates that the GOSD provides superior contrast than the Anger camera for every tumor to collimator distance and for every tumor dimension. Also, signal-to-noise ratio (SNR), full-width at half-maximum (FWHM), and full-width at tenth maximum (FWTM) show a better response for the germanium pixellated detector with respect to Anger camera due to better energy and spatial resolution of the germanium-based device. 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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