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Nuclear Science, IEEE Transactions on

Issue 1  Part 2 • Date Feb. 2008

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Displaying Results 1 - 21 of 21
  • [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): 449 - 450
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  • Dynode-Timing Method for PET Block Detectors

    Page(s): 451 - 456
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (976 KB) |  | HTML iconHTML  

    The focus of this paper is the investigation of a new dynode-timing technique optimized for PET block detectors. This method allows utilization of dynode signals from single but especially multiple photo-multiplier tubes (PMTs), operated with negative high-voltage. The technique will provide an event-timing trigger without deteriorating the anode signal. A printed circuit board has been developed and built for this investigation. Benchmark measurements have been performed, comparing timing of the anode signal with timing of the inverted last-dynode signal and timing of the dynode signal extracted via a newly developed LVPECL-logic based board. Timing measurements were performed with plastic as well as LSO scintillators. From single PMT measurements we find a 30 ps improvement with the dynode-timing method compared to the standard anode timing with two Photonis XP2020Q PMTs with LSO (10 mmtimes10 mmtimes10 mm). For a quad-PMT block detector, assembled of four Hamamatsu R9800 with a Hi-Rez block, the timing-resolution improves ~10%, by 43 ps compared to the standard anode timing. View full abstract»

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  • New 9 ,\times, 9 and 10 ,\times, 10 BGO Block Detector for Human PET Using PMT Quadrant Sharing Design

    Page(s): 457 - 462
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1236 KB) |  | HTML iconHTML  

    Our objectives were to develop two 9times9 and 10times10 array high resolution position sensitive block detectors using low cost photomultiplier-quadrant-sharing (PQS) technology. These two blocks can decode 4.3 mm or 3.9 mm BGO crystals with 39 mm size regular round PMT. By using ESR film as reflector between crystals, we achieved 96% packing fractions for these two blocks. Compared with conventional block design using 19 mm or 26 mm PMT, Phi39 mm size PMT can reduce the number of PMT in a camera by 55%-75%. Use of BGO crystal can reduce crystal cost by more than 70% compared to LSO or GSO crystals that are used in some of the newest PET cameras. The BGO crystal sizes-4.3 mm or 3.9 mm-in these two PQS blocks were similar to or smaller than BGO, LSO, or GSO crystals (4-6.3 mm) in commercial human PET cameras. The spatial resolution of the PQS blocks was expected to be similar or better. List mode data of these two blocks were acquired with Na- 22 source. Crystal-decoding map of blocks and individual crystal spectra were derived. All 9times9 and 10times10 crystals were clearly decoded on the block decoding map. These two PQS detectors decoded 81 or 100 BGO crystals per PMT. The average peak to valley ratio of decoding map was 3.4 and 1.8 respectively. The light collection efficiency for all crystals in the blocks were 71%-100% and 66%-100% respectively. The average energy resolutions of all crystals were 16.8% and 17.2% respectively. Our data suggest that even at lower cost the new PQS PET camera may outperform recent conventional PET cameras. View full abstract»

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  • A Multiplexer Design for Position-Sensitive Avalanche Photodiode Detectors in a PET Scanner

    Page(s): 463 - 468
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    A small-animal positron emission tomography (PET) scanner using PS-APD (position-sensitive avalanche photodiode) detectors has been developed for simultaneous PET/MRI imaging. In this scanner, up to 16 detector modules (one PS-APD per module) are used, and each detector module produces 4 signals to be digitized with their peak values. This leads to as many as 64 analog outputs to the data acquisition (DAQ) system, requiring 64 DAQ channels. In the future, the system will be extended to 32 modules, resulting in 128 channels. It is possible to sample all channels simultaneously, but most of them do not contain useful data, since only one coincidence event (producing data on 8 channels) is identified each time. The purpose of this work was to develop a general-purpose method for reducing the number of analog inputs to the data acquisition for the sparse fast analog signals produced in a PET scanner. To achieve this, a multiplexer board was designed to sample coincidence events from the PET scanner. The effect of the multiplexer on signal quality was evaluated and the average peak-to-valley ratios in detector flood histograms with and without multiplexer were 2.97 and 3.02 respectively. On-board coincidence, pile-up rejection and multiple coincidence rejection functions were implemented and worked as expected. The dead time performance was also characterized. View full abstract»

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  • Effect of Temperature on the Performance of Proportional APD-Based Modules for Gamma Ray Detection in Positron Emission Tomography

    Page(s): 469 - 480
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    MADPET-II is a small animal PET tomograph that features individual lutetium oxyorthosilicate (LSO) crystal readout from avalanche photodiodes (APDs). The detector signals are preamplified by 16-channel fully integrated ASICs which are placed as close as possible to the detector in order to avoid attenuation of the signal or unwanted stray capacitance. However, the power consumption of the preamplifier (30 mW per channel) can cause heat transfer and, consequently, gain drift to temperature sensitive detectors. Temperature measurements on the front-end electronics of MADPET-II have shown a maximum increase of approximately 30 C in the area around the preamplifier and in the area around the APD-LSO detector with respect to room temperature. In the presence of this temperature gradient, energy spectra have been acquired from which a significant drift of the photopeak (3.4% per C) and a small increase of the mean energy resolution (3% over the whole temperature range studied) with increasing temperature has been observed. The effect of temperature on the time resolution is small in comparison to the effect of walk and jitter introduced by the analog processing electronics. The behavior of two 48 LSO-APD front-end detector arrays in coincidence at temperatures below ambient and at various values of the APD bias voltage in terms of energy and time resolution has also been studied. The total current drawn by the APDs (leakage current and photocurrent) has been monitored at various temperatures and APD bias and was modelled and fitted by a theoretical function demonstrating a and dependence. No significant improvement on time resolution with decreasing temperature has been observed. For temperature stabilization and monitoring, thermoelectric cooling is considered appropriate for mounting in the limited free space of a PET scanner, especially when this is inside an MR scanner for simultaneous PET/MR imaging. View full abstract»

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  • High-Resolution ^{125} I Small Animal Imaging With a Coded Aperture and a Hybrid Pixel Detector

    Page(s): 481 - 490
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    We report on tests of a radionuclide imaging system for in vivo investigations in small animals with low-energy photons as from 125I (27-35 keV). Imaging optics features a high-resolution coded aperture mask and a fine pitch hybrid pixel detector (silicon 300-mum or 700-mum thick, or CdTe 1 mm thick) of the Medipix2 series (55 mum pitch, 256 x 256 pixels). The coded aperture had 480 70-mum holes in 100-mum-thick tungsten. Laboratory tests with a 109Cd 22 keV source and a microfocus X-ray tube (35 kVp, Mo anode) show a system resolution of about 110 mum at magnification m = 2.12 and a sensitivity improvement of 30:1 as compared to a 300-mum pinhole collimator. The field of view also depends on magnification: in the experiments presented, it varied from 6 mm (m = 2.12) to 21 mm (m = 0.66). 125I in vivo mouse thyroid imaging with the 70 mum coded aperture, a 300 mum pinhole and a 100 mum parallel hole collimator was also performed to obtain a qualitative comparison. This low energy, semiconductor-based, compact gamma-ray imaging system can be used as a gamma-ray sub-millimeter resolution imager for energies below about 35 keV and it is the basic imaging unit of a small animal Single Photon Emission Computed Tomography system (MediSPECT) built at University of Napoli Federico II and Istituto Nazionale Fisica Nucleare (INFN), Napoli. View full abstract»

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  • A Monte Carlo Model for Energy Spectra Analysis in Dedicated Nuclear Breast Imaging

    Page(s): 491 - 500
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1934 KB) |  | HTML iconHTML  

    A Monte Carlo model for dedicated nuclear breast imaging was developed using the Monte Carlo N-particle (MCNP) code. The modeled gamma camera was the LumaGem 3200s system, which comprised a 96 times128 array of cadmium zinc telluride (CZT) elements with 1.6 times 1.6 mm2 and was equipped with a high sensitivity collimator. The patient model consisted of an 800-mL breast compressed to a thickness of 5.5 cm and an adjacent 8000-mL torso containing compartments modeling the liver and heart. Energy spectra from patients were acquired to determine an average patient energy spectrum. A phantom simulation was performed to determine the activity concentration in liver and heart regions versus the torso cavity and breast that produced an energy spectrum most closely matching the average patient spectrum. The Monte Carlo simulation was performed to simulate the energy spectra and breast images acquired from patient studies. The simulation allowed changes in intrinsic energy resolution of the detector and energy window. A correction to model the tailing effect in the CZT was also developed. The spectral components and their contribution to the energy windowed image were examined and the effect of changes in energy resolution on tumor contrast was determined. Results showed that 13-19% of counts in the breast image are scattered events (primarily first order Compton) and scatter from the torso region accounts for less than 4% of counts in the breast image for energy resolutions between 3.9-20%. Events from the torso are concentrated at the chest wall edge of the detector's field of view, consequentially decreasing tumor contrast in this area. Because of low overall scatter in the breast, changes in energy resolution were found to have minimal effect on tumor contrast. View full abstract»

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  • Neutron Stimulated Emission Computed Tomography for Diagnosis of Breast Cancer

    Page(s): 501 - 509
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (345 KB) |  | HTML iconHTML  

    Neutron stimulated emission computed tomography (NSECT) is being developed as a non-invasive spectroscopic imaging technique to determine element concentrations in the human body. NSECT uses a beam of fast neutrons that scatter inelastically from atomic nuclei in tissue, causing them to emit characteristic gamma photons that are detected and identified using an energy-sensitive gamma detector. By measuring the energy and number of emitted gamma photons, the system can determine the elemental composition of the target tissue. Such determination is useful in detecting several disorders in the human body that are characterized by changes in element concentration, such as breast cancer. In this paper we describe our experimental implementation of a prototype NSECT system for the diagnosis of breast cancer and present experimental results from sensitivity studies using this prototype. Results are shown from three sets of samples: (a) excised breast tissue samples with unknown element concentrations, (b) a multi-element calibration sample used for sensitivity studies, and (c) a small-animal specimen, to demonstrate detection ability from in-vivo tissue. Preliminary results show that NSECT has the potential to detect elements in breast tissue. Several elements were identified common to both benign and malignant samples, which were confirmed through neutron activation analysis (NAA). Statistically significant differences were seen for peaks at energies corresponding to 37Cl, 56Fe, 58Ni, 59Co, 79Br and 87Rb. The spectrum from the small animal specimen showed the presence of 12C from tissue, from bone, and elements 39K, 27Al, 37Cl, 56Fe, 68Zn and 25Mg. Threshold sensitivity for the four elements analyzed was found to range from 0.3 grams to 1 gram, which is higher than the microgram sensitivity required for cancer detection. Patient do- se levels from NSECT were found to be comparable to those of screening mammography. View full abstract»

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  • Digital Coincidence Processing for the RatCAP Conscious Rat Brain PET Scanner

    Page(s): 510 - 515
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1466 KB) |  | HTML iconHTML  

    The RatCAP has been designed and constructed to image the awake rat brain. In order to maximize system performance, offline digital coincidence data processing algorithms including offset delay correction and prompt and delayed coincidence detection have been developed and validated. With offset delay correction using a singular value decomposition (SVD) technique, overall time resolution was improved from 32.6 to 17.6 ns FWHM. The experimental results confirm that the ratio of prompts to randoms was improved because a narrower timing window could be used. 18F-fluoride rat bone scan data were reconstructed using our fully 3-D ML-EM algorithm with a highly accurate detector response model created from Monte Carlo simulation. View full abstract»

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  • Counting Rates Modeling for PET Scanners With GATE

    Page(s): 516 - 523
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    Several developments were made in the GATE simulation platform to allow accurate modeling of the count rate performances of PET scanners over a wide range of activity concentrations. A background noise module, a dead time and limited bandwidth modeling for the coincidences, and a delayed coincidence builder were added in the code. The results obtained for the modeling of the ECAT HRRT and Focus 220 scanners with the newly developed modules are discussed. They show that GATE can be used to accurately simulate the single event, prompt coincidence and delayed coincidence rates, from very low activity levels in the field of view up to levels that saturate the acquisition system. The new developments were committed into the public release of GATE, making them available for the whole community, thanks to the open source license under which GATE is published (LGPL). View full abstract»

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  • Axial Resolution of Helical-Orbit Pinhole SPECT With Synchronized and Unsynchronized Motion

    Page(s): 524 - 530
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    Pinhole SPECT imaging is widely used in small-animal imaging. Helical orbits provide better sampling and axial resolution compared to circular ones; however, the unsynchronized axial translation of the imaged object and the camera rotation may cause blurring in the image resulting in poorer resolution. In this study, we investigated the axial resolution for synchronized and unsynchronized motions with a small phantom (Ultra-Micro-Defrise) that closely mimics the size of a mouse. We applied angular-dependent axial mechanical shift corrections that substantially improved axial resolution in this regime. Further, we developed custom-designed electronic circuitry to achieve synchronization of the SPECT scanner and the imaged object. The results show that synchronized motion improves axial resolution especially when the angular step of the scanner's rotation is large. View full abstract»

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  • Wall Motion Estimation for Gated Cardiac Emission Tomography: Physical Phantom Evaluation

    Page(s): 531 - 536
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    The purpose of this work was to evaluate myocardial wall motion estimation methods for gated cardiac emission tomography using a dynamic, physical phantom. Wall motion has been increasingly used in 4D image reconstruction methods for improved image quality. A commercially available dynamic phantom was modified by attaching radioactive markers to the phantom myocardial wall. The markers were used to provide an independent measurement of the wall motion throughout the cardiac cycle during a gated SPECT acquisition. Then, without moving the phantom, and after the markers were allowed to decay to negligible levels, the myocardium was injected with 99mTc and a gated SPECT scan was acquired. Two wall motion estimation methods were applied to the gated SPECT data. The first method was a standard optical flow algorithm applied to OSEM reconstructions of the myocardial emission data. The second was a simultaneous image reconstruction/motion estimation algorithm. The error in the estimated motion fields was described by the average vector difference between the motion of the markers and the estimated myocardial motion. The simultaneous method gave more accurate motion estimates compared with the optical flow method, and this was more pronounced for larger motion magnitudes. The absolute differences were not great, and the practical implications of these findings are not certain. The physical phantom proved to be an effective tool for evaluating motion estimation methods. View full abstract»

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  • Spillover Compensation in the Presence of Respiratory Motion Embedded in SPECT Perfusion Data

    Page(s): 537 - 542
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    Spillover from adjacent significant accumulations of extra-cardiac activity decreases diagnostic accuracy of SPECT perfusion imaging in especially the inferior/septal cardiac region. One method of compensating for the spillover at some location outside of a structure is to estimate it as the counts blurred into this location when a template (3D model) of the structure undergoes simulated imaging followed by reconstruction. The objective of this study was to determine what impact uncorrected respiratory motion has on such spillover compensation of extra-cardiac activity in the right coronary artery (RCA) territory, and if it is possible to use manual segmentation to define the extra-cardiac activity template(s) used in spillover correction. Two separate MCAT phantoms (1283 matrices) were simulated to represent the source and attenuation distributions of patients with and without respiratory motion. For each phantom the heart was modeled: 1) with a normal perfusion pattern and 2) with an RCA defect equal to 50% of the normal myocardium count level. After Monte Carlo simulation of 64times64times120 projections with appropriate noise, data were reconstructed using the rescaled block iterative (RBI) algorithm with 30 subsets and 5 iterations with compensation for attenuation, scatter and resolution. A 3D Gaussian post-filter with a sigma of 0.476 cm was used to suppress noise. Manual segmentation of the liver in filtered emission slices was used to create 3D binary templates. The true liver distribution (with and without respiratory motion included) was also used as binary templates. These templates were projected using a ray-driven projector simulating the imaging system with the exclusion of Compton scatter and reconstructed using the same protocol as for the emission data, excluding scatter compensation. Reconstructed templates were scaled using reconstructed emission count levels from the liver, and spillover subtracted outside the template. It was evident from the p- olar maps that the manually segmented template reconstructions were unable to remove all the spillover originating in the liver from the inferior wall. This was especially noticeable when a perfusion defect is present. Templates based on the true liver distribution appreciably improved spillover correction. Thus the emerging combined SPECT/CT technology may play a vital role in identifying and segmenting extra-cardiac structures more reliably thereby facilitating spillover correction. This study also indicates that compensation for respiratory motion might play an important role in spillover compensation. View full abstract»

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  • Normalisation of Histogrammed List Mode Data

    Page(s): 543 - 551
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1384 KB) |  | HTML iconHTML  

    Many PET scanners nowadays have the possibility to record event-by-event information, known as list mode data. This has the advantage of keeping the data in the highest possible resolution (both temporal and spatial). In most cases, list mode data are then binned into sinogram format before reconstruction. In this paper, we discuss at which stage normalisation factors should be introduced. It is shown that noise is greatly reduced by performing the normalisation after the binning. We illustrate this with acquired and simulated data for the quad HiDAC camera. View full abstract»

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  • An Improved Form of Linogram Algorithm for Image Reconstruction

    Page(s): 552 - 559
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (529 KB) |  | HTML iconHTML  

    The implementation of the discrete ramp filter in the filtered backprojection (FBP) algorithms has been carefully investigated by Kak and Slane in Principles of Computerized Tomographic Imaging. In the linogram algorithms, however, it was rarely used in a correct way. Instead, an oversampling (zero-padding) factor of four is usually taken to reduce the dishing artifacts. We here improve the linogram algorithm by using a new strategy of weighting instead of in its original implementation. The new weighting is produced via the Fourier transform of the discrete ramp filter similar to that in Kak and Slaney. We explicitly derive the connection between the oversampling processing and the implementation of the discrete ramp filter in the spatial domain: if projection data are zero-padded to double length, with the discrete ramp filter, the effect is theoretically equivalent to zero-padding infinitely long in the original implementation; without zero-padding, the modified algorithm can obtain almost accurate reconstruction in the central part of an image. Our theoretical analysis also gives the optimal way of implementing the linogram algorithm, leading to savings in computational time and memory space. Results of theoretical analysis are validated by numerical simulations. View full abstract»

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  • Accelerated SPECT Monte Carlo Simulation Using Multiple Projection Sampling and Convolution-Based Forced Detection

    Page(s): 560 - 567
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    Monte Carlo (MC) is a well-utilized tool for simulating photon transport in single photon emission computed tomography (SPECT) due to its ability to accurately model physical processes of photon transport. As a consequence of this accuracy, it suffers from a relatively low detection efficiency and long computation time. One technique used to improve the speed of MC modeling is the effective and well-established variance reduction technique (VRT) known as forced detection (FD). With this method, photons are followed as they traverse the object under study but are then forced to travel in the direction of the detector surface, whereby they are detected at a single detector location. Another method, called convolution-based forced detection (CFD), is based on the fundamental idea of FD with the exception that detected photons are detected at multiple detector locations and determined with a distance-dependent blurring kernel. In order to further increase the speed of MC, a method named multiple projection convolution-based forced detection (MP-CFD) is presented. Rather than forcing photons to hit a single detector, the MP-CFD method follows the photon transport through the object but then, at each scatter site, forces the photon to interact with a number of detectors at a variety of angles surrounding the object. This way, it is possible to simulate all the projection images of a SPECT simulation in parallel, rather than as independent projections. The result of this is vastly improved simulation time as much of the computation load of simulating photon transport through the object is done only once for all projection angles. The results of the proposed MP-CFD method agrees well with the experimental data in measurements of point spread function (PSF), producing a correlation coefficient (r2) of 0.99 compared to experimental data. The speed of MP-CFD is shown to be about 60 times faster than a regular forced detection MC program with similar results. View full abstract»

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    Page(s): 568
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  • IEEE Transactions on Nuclear Science information for authors

    Page(s): C3
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    Page(s): C4
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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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