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Nuclear Science, IEEE Transactions on

Issue 5  Part 1 • Date Oct. 2005

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

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

    Page(s): c2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 1225 - 1226
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  • Optimization of acquisition parameters for simultaneous 201Tl and 99mTc dual-isotope myocardial imaging

    Page(s): 1227 - 1235
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1344 KB) |  | HTML iconHTML  

    In 201Tl/99mTc dual-isotope simultaneous-acquisition (DISA) myocardial imaging, crosstalk due to Tc photons results in significant contamination of the Tl data. The objective of this work is to seek the acquisition parameters (i.e., energy window width and center) that have the optimal tradeoff between minimizing the crosstalk and maximizing the detection efficiency. The optimization criterion was based on maximizing an ideal observer signal-to-noise ratio (SNR) for the myocardial defect detection task using single-isotope and DISA projection images acquired from a torso phantom. For single-isotope images, the optimal energy windows (width/center: 26 keV/75 keV and 28 keV/165 keV for 201Tl, 30 keV/142 keV for 99mTc) are wider than typical windows. For DISA imaging, the optimal windows varied with the 99mTc to 201Tl activity ratio and are thus likely to depend on the uptake ratio in each patient. Using the optimal ratio 2.25-2.75 (148 MBq 201Tl and 333-407 MBq 99mTc) with the corresponding optimal windows (22 keV/72 keV, 24 keV/167 keV, and 24 keV/140 keV) gives 201Tl images with substantially increased SNRs as well as 99mTc images with SNRs same as those of 370 MBq 99mTc-only images. However, without the addition of crosstalk compensation, the use of the optimal activity and energy windows alone is likely not sufficient to restore the DISA Tl SNR to that of Tl-only image. View full abstract»

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  • Measuring the variation in radius of rotation as a function of gantry angle for ultra-high-resolution pinhole SPECT

    Page(s): 1236 - 1242
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    Pinhole SPECT is sensitive to alignment and calibration. For circular orbits, it is typically assumed that the radius of rotation (ROR) is constant. Uncompensated deviation in the ROR from a constant has the potential to worsen resolution. Herein, we describe a method for determining the ROR as a function of gantry angle. This method uses a laser to serve as a reference line and a laser target mounted to the pinhole collimator to measure position. The target rotates with the collimator and is read-out at multiple angles. The two-dimensional read-out values are used to calculate the ROR as a function of angle. Experimental radionuclide SPECT projection data were acquired. The projection data were reconstructed using the angular-dependent correction and using an average ROR. The results indicate that it is difficult to distinguish the effect of this correction when the amplitude is less than about 0.5 mm. However, the correction is very pronounced for an amplitude of about 1 mm. View full abstract»

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  • Initial study of quasi-monochromatic X-ray beam performance for X-ray computed mammotomography

    Page(s): 1243 - 1250
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    We evaluate the feasibility, benefits, and operating parameters of a quasimonochromatic beam for a newly developed x-ray cone beam computed mammotomography application. The value of a near monochromatic x-ray source for fully 3D dedicated mammotomography is the expected improved ability to separate tissues with very small differences in attenuation coefficients while maintaining dose levels at or below that of existing dual view mammography. In previous studies, simulations for a range of tungsten tube potentials, K-edge filter materials, filter thicknesses, and a 12 cm uncompressed breast, with a digital flat-panel CsI(Tl) detector model, indicated that thick, rare earth filter materials may provide optimized image quality. Figures of merit computed included: lesion contrast under different filtering conditions; ratio of measured lesion contrast with and without filtering; and exposure efficiency (SNR2/exposure). Initial experiments are performed with a custom built x-ray mammotomography system, cerium foil filters, and plastic breast and lesion tissue-equivalent slabs. Simulation results showed that tube potentials of 50-70 kVp with filters of Z=57-63 yielded quasimonochromatic x-ray spectra with improved FOMs. Initial experimental measurements corroborate simulation results in that, relative trends and rank order of contrast ratios and exposure efficiency were in agreement. These studies show that this approach can be implemented practically with simple hardware and yield improved exposure efficiency versus the unfiltered or minimally filtered case. View full abstract»

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  • Comparison of compact gamma cameras with 1.3- and 2.0-mm quantized elements for dedicated emission mammotomography

    Page(s): 1251 - 1256
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    In an effort to image smaller breast lesions, two compact gamma cameras with different intrinsic NaI(Tl) pixel sizes are evaluated for use in the application specific emission tomography (ASET) system for dedicated mammotomographic emission imaging. Comparison measurements were made with two scintillator arrays having 1.3×1.3×6 mm3 or 2.0×2.0×6 mm3 elements on exactly the same set of PMTs, electronics and control/processing hardware. Uniformity, sensitivity and energy resolution were assessed with flood field phantoms. Spatial resolution measurements included: a 99mTc (140 keV) activity filled capillary tube imaged in planar mode from 1-10 cm distance; two such tubes separated by 2 cm were also imaged with simple circular tomography from 3-7 cm radii-of-rotation (RORs); and a 99mTc filled mini cold-rod phantom was imaged at 5 cm ROR with a simple circular orbit. Finally, a freely suspended and uniformly filled 950 mL breast phantom containing four fillable lesions (4-10 mm dia) was imaged with a lesion-to-uniform-background activity concentration ratio of 15:1, using simple and complex three-dimensional (3-D) orbits and minimal RORs. The measured sensitivity varied by the crystal fill-factor; uniformity had <4% variability; and mean energy resolutions of each camera were ≤12% full-width at half-maximum (FWHM). The planar spatial resolutions correspond to calculated values, with smaller pixels yielding 2%-13% better resolution with decreasing separation distance; tomographic results ranged from 3.2-5.2 mm FWHM at 3-7 cm, with nominally better contrast-resolution for the smaller pixel camera. Consistent with signal detection characteristics for these measurement conditions, quantitative SNRs and contrasts from lesion imaging with the uniform breast background illustrate better overall performance under nearly all conditions and for all lesions for the larger pixel camera. View full abstract»

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  • Quantum efficiency of the MCP detector: Monte Carlo calculation

    Page(s): 1257 - 1262
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    A prototype scanning-slit X-ray imaging system with microchannel plate (MCP) detector has recently been developed and tested for potential applications in medical imaging. For this purpose, the quantum efficiency of the MCP needs to be calculated and verified experimentally for polychromatic X-ray beams. X-ray detection in the MCP is a cascade of several processes including the absorption of the photon in the MCP material, the escape of created fast (photo, Compton, or Auger) electrons from the MCP channel walls into the channels, triggering an avalanche of secondary electrons in the microchannels, and detecting the resulted charge pulse. Because electron transport in the material is involved in this process, Monte Carlo simulations were used to calculate the quantum efficiency of an MCP for photon beams used in mammography, computed tomography (CT), and chest radiography. The quantum efficiency of the MCP with 5-μm channel diameter was calculated to be 68%, 89%, and 81% at X-ray tube voltages of 45, 90, and 120 kVp, which are used in scanning slit mammography, breast CT, and chest radiography, respectively. The detection efficiencies of an MCP with 2 μm channel diameter was calculated to be 91%, 92%, and 86% at 45, 90, and 120 kVp tube voltages, respectively. The efficiency of a recently introduced silica MCP (pure SiO2) with 5 μm channel diameter was calculated to be 86% and 76% at 35 kVp and 45 kVp, respectively, and is rapidly decreased at higher energies. Results of the calculations show that the detection efficiencies of the MCPs are comparable to the currently available detectors in the medical X-ray imaging. View full abstract»

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  • Improved scatter correction for SPECT images: a Monte Carlo study

    Page(s): 1263 - 1270
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (912 KB) |  | HTML iconHTML  

    We propose the extended triple energy window (ETEW) method that improves quantitation and contrast in SPECT images. ETEW is a modification of the triple energy window (TEW) method which corrects for scatter by using abutted scatter rejection windows, which can overestimate or underestimate scatter. ETEW is compared to TEW using Monte Carlo simulated data for point sources as well as hot and cold spheres in a cylindrical water phantom. Various main energy window widths were simulated. Both TEW and ETEW improved image contrast and recovery coefficients. Estimated scatter components by TEW were not proportional to the true scatter components when main energy window widths of 10%, 15%, and 20% were simulated. ETEW resulted in scatter that was directly proportional to the true scatter. ETEW improves image quantitation and quality of SPECT image data by more accurately correcting for scatter. View full abstract»

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  • Measurement of centi-Gray X-ray dose levels with radiochromic film

    Page(s): 1271 - 1273
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    X-ray doses in the range of centi-Gray can be detected and accurately measured on a relative scale for low energy X-rays using a high sensitivity radiochromic film stack. Gafchromic XR type T radiochromic film has been investigated to analyze its ability to measure relative doses below 50 cGy for 100-kVp X-rays using a layered technique. Investigations showed that a 4-layer film stack could produce reproducible results at 50-cGy relative applied dose to within 3% and to within 12% for 5-cGy applied dose. The combination of single sheet higher film sensitivity to low energy X-rays along with a layered film dosimetry technique provides the ability to adequately measure low relative absorbed doses less than 50 cGy if required. View full abstract»

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  • Speedup OS-EM image reconstruction by PC graphics card technologies for quantitative SPECT with varying focal-length fan-beam collimation

    Page(s): 1274 - 1280
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    In this paper, we present a new hardware acceleration method to speedup the ordered-subsets expectation-maximization (OS-EM) algorithm for quantitative single photon emission computed tomography (SPECT) image reconstruction with varying focal-length fan-beam (VFF) collimation. By utilizing the geometrical symmetry of VFF point-spread function (PSF), compensation for object-specific attenuation and system-specific PSF are accelerated using currently available PC video/graphics card technologies. A tenfold acceleration of quantitative SPECT reconstruction is achieved. View full abstract»

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  • A new multimodality system for quantitative in vivo studies in small animals: combination of nuclear magnetic resonance and the radiosensitive β-MicroProbe

    Page(s): 1281 - 1287
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    Elucidating complex physiological mechanisms in small animal in vivo requires the development of new investigatory techniques including imaging with multiple modalities. Combining exploratory techniques has the tremendous advantage to record simultaneously complementary parameters on the same animal. In this field, an exciting challenge remains in the combination of nuclear magnetic resonance (NMR) and positron emission tomography (PET) since small animals studies are limited by strict technical constraints in vivo. Coupling NMR with a radiosensitive β-MicroProbe offers therefore an interesting technical alternative. To assess the feasibility of this new dual-modality system, we designed theoretical and experimental approaches to test the ability of the β-Microprobe to quantify radioactivity concentration in an intense magnetic field. In an initial step, simulations were carried out using Geant4. First, we evaluated the influence of a magnetic field on the probe detection volume. Then, the detection sensitivity and energy response of the probe were quantified. In a second step, experiments were run within a 7-T magnet to confirm our simulations results. We showed that using the probe in magnetic fields leads to a slight attenuation in sensitivity and an increase of the scintillation light yield. These data demonstrate the feasibility of combining NMR to the β-MicroProbe. View full abstract»

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  • A robust visual tracking system for patient motion detection in SPECT: hardware solutions

    Page(s): 1288 - 1294
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1808 KB) |  | HTML iconHTML  

    Our overall research goal is to devise a robust method of tracking and compensating patient motion by combining an emission data based approach with a visual tracking system (VTS) that provides an independent estimate of motion. Herein, we present the latest hardware configuration of the VTS, a test of the accuracy of motion tracking by it, and our solution for synchronization between the SPECT and the optical acquisitions. The current version of the VTS includes stereo imaging with sets of optical network cameras with attached light sources, a SPECT/VTS calibration phantom, a black stretchable garment with reflective spheres to track chest motion, and a computer to control the cameras. The computer also stores the JPEG files generated by the optical cameras with synchronization to the list-mode acquisition of events on our SPECT system. Five Axis PTZ 2130 network cameras (Axis Communications AB, Lund, Sweden) were used to track motion of spheres with a highly retroreflective coating using stereo methods. The calibration phantom is comprised of seven reflective spheres designed such that radioactivity can be added to the tip of the mounts holding the spheres. This phantom is used to determine the transformation to be applied to convert the motion detected by the VTS into the SPECT coordinates system. The ability of the VTS to track motion was assessed by comparing its results to those of the Polaris infrared tracking system (Northern Digital Inc., Waterloo, ON, Canada). The difference in the motions assessed by the two systems was generally less than 1 mm. Synchronization was assessed in two ways. First, optical cameras were aimed at a digital clock and the elapsed time estimated by the cameras was compared to the actual time shown by the clock in the images. Second, synchronization was also assessed by moving a radioactive and reflective sphere three times during concurrent VTS and SPECT acquisitions and comparing the time at which motion occurred in the optical and SPECT images. The results show that optical and SPECT images stay synchronized within a 150-ms range. The 100-Mbit network load is less than 10%, and the computer's CPU load is between 15% and 25%; thus, the VTS can be improved by adding more cameras or by increasing the image size and/o- r resolution while keeping an acquisition rate of 30 images per second per camera. View full abstract»

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  • An instantaneous photomultiplier tube gain-tuning method for PET or gamma camera detectors using an LED network

    Page(s): 1295 - 1299
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    A photomultiplier tube (PMT) gain can change with many environmental factors, such as room temperature, patient load, short-term or long-term radiation exposure, and time. Unbalanced PMT gains degrade the image resolution and quality in a positron emission tomography (PET) camera or a gamma camera. This paper presented a new method to instantaneously recover the original manufacture PMT gain setting using a blue light-emitting diode (LED) network. Each LED shines directly into the center of a scintillation crystal block from the PMT side, and the light is collected by the surrounding PMTs. The gain tuning is done by changing the gains of these surrounding PMTs or their following amplifiers to have the same signal output. An LED has well-known problems of large light-yield varieties and is very sensitive to temperature. To overcome these problems, the light outputs of two neighboring LEDs are aligned first by a shared PMT. Each LED flashes at 250-KHz pulse rate, the data acquisition for the gain tuning can be finished within a very short time so the LED temperature effect can be ignored. The amount of LED light output is set as close as possible to the amount of scintillation light by programming the width or height of the pulses; therefore, the same electronics can be used for data acquisition and tuning. We estimated a 12 module PET camera with 924 PMTs in a PMT-quadrant-sharing design can be tuned in 1 min. View full abstract»

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  • A central positron source to perform the timing alignment of detectors in a PET scanner

    Page(s): 1300 - 1304
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    Accurate timing alignment and stability are important to maximize the true counts and minimize the random counts in positron emission tomography. Its importance increases in time-of-flight (TOF) scanners. We propose using a central positron emitting source enclosed in a detector which detects the excess energy of the positron before it annihilates as a timing reference. All crystals can be time-aligned with respect to this central source. We evaluated 10 μCi 22Na and 68Ge sources embedded in cylinders of plastic scintillator coupled to a fast PMT. Light flashes produced after the parent isotope emits positrons are detected, and the anode signals from the PMT are the reference time for each positron decay. The time delay before the gamma ray is detected by the scanner's conventional gamma ray detectors is the time offset to be applied to that crystal. Since all detectors are almost the same distance from the central source, TOF errors are minimized. Preliminary results show a mean signal amplitude of >0.5 V from 22Na at 1000-V PMT bias, a timing FWHM of 850 ps with respect to a small LSO crystal. This suggests it could be useful to align both conventional and TOF PET scanners. View full abstract»

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  • System performance Simulations of the RatCAP awake rat brain scanner

    Page(s): 1305 - 1310
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (744 KB) |  | HTML iconHTML  

    The capability to create high quality images from data acquired by the Rat Conscious Animal PET tomograph (RatCAP) has been evaluated using modified versions of the PET Monte Carlo code Simulation System for Emission Tomography (SimSET). The proposed tomograph consists of lutetium oxyorthosilicate (LSO) crystals arranged in 12 4 × 8 blocks. The effects of the RatCAPs small ring diameter (∼40 mm) and its block detector geometry on image quality for small animal studies have been investigated. Since the field of view will be almost as large as the ring diameter, radial elongation artifacts due to parallax error are expected to degrade the spatial resolution and thus the image quality at the edge of the field of view. In addition to Monte Carlo simulations, some preliminary results of experimentally acquired images in both two-dimensional (2-D) and 3-D modes are presented. View full abstract»

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  • First-pass angiography in mice using FDG-PET: a simple method of deriving the cardiovascular transit time without the need of region-of-interest drawing

    Page(s): 1311 - 1315
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    In this study, we developed a simple and robust semi-automatic method to measure the right ventricle to left ventricle (RV-to-LV) transit time (TT) in mice using 2-[18F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET). The accuracy of the method was first evaluated using a 4-D digital dynamic mouse phantom. The RV-to-LV TTs of twenty-nine mouse studies were measured using the new method and compared to those obtained from the conventional ROI-drawing method. The results showed that the new method correctly separated different structures (e.g., RV, lung, and LV) in the PET images and generated corresponding time activity curve (TAC) of each structure. The RV-to-LV TTs obtained from the new method and ROI method were not statistically different (p=0.20; r=0.76). We expect that this fast and robust method is applicable to the pathophysiology of cardiovascular diseases using small animal models such as rats and mice. View full abstract»

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  • Improved prostate cancer imaging with SPECT/CT and MRI/MRSI

    Page(s): 1316 - 1320
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB) |  | HTML iconHTML  

    We propose a combined imaging technique for prostate cancer using 111In-ProstaScint SPECT/CT and MRI/MRSI. When used alone, either SPECT/CT or MRI/MRSI has limitations in assessing the patient undergoing clinical prostate cancer management. However, combined imaging can use MRI/MRSI to assess the prostate gland while SPECT/CT 111In-ProstaScint imaging can evaluate nearby and distant lymph nodes for metastases. The combined imaging study thereby provides complementary information useful for the cancer management. 111In-ProstaScint SPECT data are reconstructed using an iterative algorithm that includes CT-derived attenuation correction and depth-dependent collimator blurring compensation. 3D MR spectra are overlaid on the T2-weighted MR image. Image data from 3 patient studies demonstrate the potential role of combined 111In-ProstaScint SPECT/CT and MRI/MRSI imaging of prostate cancer. In the first, SPECT/CT revealed increased uptake of 111In-ProstaScint, but that occurred beyond the sensitive region of MRSI. Images from a second patient sequentially received 111In-ProstaScint SPECT/CT and MRI/MRSI in one and half months and were correlative and complementary to each other. Images from a third patient who had undergone androgen deprivation therapy show that MRI improved anatomical definition in comparison to CT, with 111In-ProstaScint indicating disease where MRSI was either equivocal or indicated atrophy. Overall, MRI/MRSI generally provided better specificity for the cancer detection within the prostate in the absence of androgen deprivation therapy, and better anatomic details of the prostate than 111In-ProstaScint SPECT/CT. Yet, 111In-ProstaScint SPECT/CT improves sensitivity for detection of distant lymph node metastases, and also is more sensitive when the patient is undergoing androgen deprivation therapy and thereby provides useful diagnostic information that complements the MRI/MRSI study alone. View full abstract»

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  • PET-SORTEO: validation and development of database of Simulated PET volumes

    Page(s): 1321 - 1328
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB) |  | HTML iconHTML  

    We present here the features and validation results of a Monte Carlo-based PET simulation platform designed to address the increasing need of simulated studies. The simulation tool, named PET-SORTEO, includes i) the generation of the raw data in accordance with both the numerical phantom description as well as with the scanner geometry and physical characteristics, and ii) the correction and reconstruction of the raw data. Validation results show that the platform reliably reproduces the image formation processes and includes correctly the sources of noise and biases. This platform allows for parallel processing and complete dynamic PET studies, including emission and transmission data, can be generated within few hours using a cluster of machines. Using PET-SORTEO, we generated a database of realistic simulated PET data accounting for inter-subject anatomical variability. This database has the merit to provide the community with realistic simulated 3D and 4D PET studies for commonly used radiotracers. This database as well as information about PET-SORTEO can be found at the address: http://sorteo.cermep.fr. View full abstract»

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  • A hybrid approach to Simulate X-ray imaging techniques, combining Monte Carlo and deterministic algorithms

    Page(s): 1329 - 1334
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    In this paper, we propose a hybrid approach to simulate multiple scattering of photons in objects under X-ray inspection, without recourse to parallel computing and without any approximation sacrificing accuracy. Photon scattering is considered from two points of view: it contributes to X-ray imaging and to the dose absorbed by the patient. The proposed hybrid approach consists of a Monte Carlo stage followed by a deterministic phase, thus taking advantage of the complementarity between these two methods. In the first stage, a set of scattering events occurring in the inspected object is determined by means of classical Monte Carlo simulation. Then this set of scattering events is used to compute the energy imparted to the detector, with a deterministic algorithm based on a "forced detection" scheme. Regarding dose evaluation, we propose to assess separately the energy deposited by direct radiation (using a deterministic algorithm) and by scattered radiation (using our hybrid approach). The results obtained in a test case are compared to those obtained with the Monte Carlo method alone (Geant4 code) and found to be in excellent agreement. The proposed hybrid approach makes it possible to simulate the contribution of each type (Compton or Rayleigh) and order of scattering, separately or together, with a single PC, within reasonable computation times (from minutes to hours, depending on the required detector resolution and statistics). It is possible to simulate radiographic images virtually free from photon noise. In the case of dose evaluation, the hybrid approach appears particularly suitable to calculate the dose absorbed by regions of interest (rather than the entire irradiated organ) with computation time and statistical fluctuations considerably reduced in comparison with conventional Monte Carlo simulation. View full abstract»

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  • Framework for iterative cone-beam micro-CT reconstruction

    Page(s): 1335 - 1340
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    We have developed a computational framework for iterative cone-beam micro-CT reconstruction. When applied to small animal imaging and other high-resolution applications, iterative algorithms pose significant implementation difficulties due to the associated high computational burden. To address this burden, we use threads and message passing (MPI) to facilitate multiprocessor cluster computing. The system matrix can be either precomputed or calculated on-the-fly. Additionally, the system matrix can be based on trilinear interpolation or volumetric intersection methods. In the case of storing the system matrix, we exploit symmetries in the cone-beam geometry to reduce the storage requirements by a factor of nearly eight. We chose simultaneous iterative reconstruction technique (SIRT) to demonstrate the framework, although other algorithms are easily implemented. When precomputing the system matrix, each iteration of SIRT completes several times faster than when using an on-the-fly system matrix computation. The precomputed method remains faster when implementing ordered subsets, but the performance advantage diminishes as the number of subsets increases. We present reconstructions of the three-dimensional (3-D) Shepp-Logan head phantom as well as mouse data acquired by a small animal X-ray CT scanner. View full abstract»

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  • Feasibility of rapid multitracer PET tumor imaging

    Page(s): 1341 - 1347
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    Positron emission tomography (PET) can characterize different aspects of tumor physiology using various tracers. PET scans are usually performed using only one tracer since there is no explicit signal for distinguishing multiple tracers. We tested the feasibility of rapidly imaging multiple PET tracers using dynamic imaging techniques, where the signals from each tracer are separated based upon differences in tracer half-life, kinetics, and distribution. Time-activity curve populations for FDG, acetate, ATSM, and PTSM were simulated using appropriate compartment models, and noisy dual-tracer curves were computed by shifting and adding the single-tracer curves. Single-tracer components were then estimated from dual-tracer data using two methods: principal component analysis (PCA)-based fits of single-tracer components to multitracer data, and parallel multitracer compartment models estimating single-tracer rate parameters from multitracer time-activity curves. The PCA analysis found that there is information content present for separating multitracer data, and that tracer separability depends upon tracer kinetics, injection order and timing. Multitracer compartment modeling recovered rate parameters for individual tracers with good accuracy but somewhat higher statistical uncertainty than single-tracer results when the injection delay was >10 min. These approaches to processing rapid multitracer PET data may potentially provide a new tool for characterizing multiple aspects of tumor physiology in vivo. View full abstract»

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  • Simultaneous, maximum-likelihood determination of focal length and source position for point-source experiments with pinhole collimation

    Page(s): 1348 - 1352
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (744 KB) |  | HTML iconHTML  

    A simple procedure to determine the focal length of a pinhole collimator is presented, which is important for planar and SPECT imaging. The procedure involves the use of a point source and three linear stages. The source is moved by carefully controlled relative shifts in two dimensions to a number of different positions within a plane nearly perpendicular to the detector's plane. For each position a projection is acquired. The focal length is calculated from the shift in the centroid of the projections via a maximum-likelihood fit. A useful byproduct of the procedure is calibration of the position of the source, which can then be used for planar imaging studies such as sensitivity and point-spread function. This calibration maps the coordinate system of the stages to the coordinate system of the aperture. The method was experimentally validated for three different focal lengths. View full abstract»

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  • Application of Monte Carlo calculation for the virtual calibration of a low-energy in vivo counting system

    Page(s): 1353 - 1358
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    Internal dose assessment can be derived from the measurement of retained activity in the whole body or in an organ at a given time. In radiation protection, this assessment, so-called in vivo measurement, is performed by an external measurement of the subject with germanium detectors (in most cases). Calibration of these detectors is ensured by anthropomorphic phantoms which, for technical reasons, can only provide rough representations of human. It is especially the case for the chest phantoms used in lung counting, subject of this paper. This leads to substantial corrections on calibration factors that are particularly crucial and delicate in low-energy in vivo measurements, resulting in important systematic errors. In order to improve calibration, former work based on numerical phantoms associated with Monte Carlo computing techniques has already proven its benefits. To go further, a Graphical User Interface called "OEDIPE", a French acronym for "tool for internal personalized dose assessment", has been developing at the IRSN internal dose assessment laboratory, simulating real measurements using person-specific computational phantoms in association with MCNP calculation code. The study presented here is dedicated to the implementation and validation of a real in vivo monitoring system (AREVA/COGEMA Marcoule, France) equipped with 4 high purity germanium (HPGe) detectors. After modeling the facility and measurement geometry using OEDIPE (design and positioning of the detectors...), validation with different configurations was carried out in two steps: first with point sources (different nuclides, different source-detector distances) and then with the Livermore calibration phantom (different overlay plates, lungs contaminated with 241Am and a mixture of actinides). The final goal is to approach a personalized numerical calibration of the facilities in order to improve dose assessment, as the use of physical phantoms for calibration induces large uncertainties. Such application could be an opening door on a better activity assessment in nuclear medicine, especially in personalized dosimetry in radioimmunotherapy. View full abstract»

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  • Comparison of penetration and scatter effects on defect contrast for GE and Siemens LEHR collimators in myocardial perfusion SPECT-a simulation study

    Page(s): 1359 - 1364
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    The goal of this paper was to evaluate the effects of collimator penetration and scatter on myocardial SPECT image quality. We chose two designs: a LEHR collimator for GE Millennium VG with a longer bore and thicker septa, and a LEHR collimator for Siemens E.CAM with a shorter bore and thinner septa. These two collimators have similar resolution properties, but very different penetration fractions. In particular, the Siemens collimator has higher detection efficiency. We used Monte Carlo (MC) simulation to simulate projection data from the three-dimensional (3-D) NCAT phantom. For each collimator, we generated three sets of projection data: the first one included only the geometric components of the collimator response, the second one included both the geometric and penetration components, and the third one included geometric, penetration and collimator scatter components. The resulting projections were reconstructed with the OSEM algorithm including attenuation and geometric response compensation. For each collimator and reconstruction, we computed the defect contrast in a short-axis slice. We found very small differences in defect contrast between the two collimators with and without penetration and collimator-scattered photons. Since the collimator with higher penetration had greater detection efficiency and showed little loss in defect contrast, a collimator with higher penetration fraction may be acceptable for use in Tc-99 m myocardial perfusion imaging. 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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