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Limiting Iterations vs. Post Smoothing for Noise Control in PET

Limiting Iterations vs. Post Smoothing for Noise Control in ...

引用

2007 IEEE nuclear Science Symposium Conference (NSS 2007), vol.7

作者： Timothy G. Turkington Joshua M. Wilson James E. Bowsher David R. Gilland Department of Biomedical Engineering Duke University Durham NC USA Graduate Program in Medical Physics Duke University Durham NC USA Department of Radiation Oncology Graduate Program in Medical Physics Duke University Durham NC 27710 USA Department of Nuclear and Radiological Engineering University of Florida Gainesville FL USA

We have performed physical phantom and simulation study with PET to compare the effects of limiting iterations and post-smoothing. The phantom was designed to mimic small hot lesions typical in FDG PET. The phantom was a body-sized 25L phantom. Eight 1cm hot spheres were filled with activity 8x the background. The phantom was scanned in 2D for 15 minutes on a GE Discovery STE. Data were framed into 1, 3, 5, and 15min frames. Images were reconstructed with a variety of subset sizes and up to 60 iterations, with corrections for attenuation, scatter, randoms, and dead-time. All image sets were post-smoothed with 4, 6, 8, 10, and 12mm FWHM Gaussian. ROI's were placed on all hot spheres, and 40 additional background ROI's were placed. Noise was measured as the variation in background ROI's. Additionally, noise was measured on a pixel-by-pixel basis as the variation over the ensemble of realizations of each frame time. Noise vs. contrast (sphere-background) were plotted for each image. The background noise method showed better results for limited iterations (～20% lower noise at a given contrast level) while the ensemble-based noise method favored post-smoothing of high iterations (with a similar ～20% difference). Similar results were obtained for simulations.

关键词： Smoothing methods Positron emission tomography Imaging phantoms Background noise Noise measurement Noise level Lesions Image reconstruction Attenuation Scattering

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A Novel Method Improving the Imaging Resolution of a Table-top Compton Camera

A Novel Method Improving the Imaging Resolution of a Table-t...

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2007 IEEE nuclear Science Symposium Conference (NSS 2007), vol.7

作者： Hee Seo Se Hyung Lee Jong Hwi Jeong Ju Hahn Lee Chun Sik Lee Jae Sung Lee Chan Hyeong Kim Department of Nuclear Engineering Hanyang University Seoul South Korea Department of Physics Chung-Ang University Seoul South Korea Department of Nuclear Medicine and Interdisciplinary Program in Radiation Applied Life Science Seoul National University Seoul South Korea

For a table-top Compton camera, which is currently under development in our group, the interaction position resolution of the absorber detector is a critical or limiting detector parameter that most seriously affects the imaging resolution of the Compton camera. Currently, it is assumed that all the interactions occur at the centers of the detector segments of the absorber detector, which is simple, but obviously not the best choice considering that the interaction depths of the photons in the absorber detector is not distributed uniformly, especially for the low-energy photons. To this end, the present study develops a novel method, called "average interaction depth (AID) method" to improve the imaging resolution of Compton camera by additionally considering the interaction depth of the incident photon in the absorber detector. Our simulation studies with Geant4 show that the imaging resolution of Compton camera can be significantly improved by using the AID method. The imaging resolution of the table-top Compton camera was improved from 9.9mm to 7.6mm in full width at half maximum (FWHM) for a 511keV γ point source. For a 364keV γ point source, the imaging resolution was improved more significantly, i.e., from 11.4mm to 7.2mm.

关键词： Image resolution Cameras

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PBMR 400 coupled code benchmark: Challenges and successes with nem-thermix

PBMR 400 coupled code benchmark: Challenges and successes wi...

引用

2006 Annual Meeting - American nuclear Society

作者： Ortensi, Javier Gougar, Hans Mkhabela, Peter Han, James Tyobeka, Bismark Ivanov, Kostadin Idaho National Laboratory Reactor Physics Division Idaho Falls ID 83415 United States Penn State University Nuclear Engineering Program State College PA 16802 United States

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Stylized versus tomographic: An experience on anatomical modeling at RPI

Stylized versus tomographic: An experience on anatomical mod...

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Monte Carlo 2005 Topical Meeting

作者： Xu, X. George Nuclear Engineering and Engineering Physics Program Rensselaer Polytechnic Institute Troy NY 12180 United States

This invited paper summarizes our experience in using both the MIRD-type stylized models and tomographic models at Rensselaer. Comparisons are made of the scaled-down version of the tomographic VIP-Man model with the stylized adult male model for external photon beams. Similar comparisons are made to a stylized pregnant woman model and a tomographic model for internal photons. The effective dose results from these two models show that they differ from each other within about 10% for common high-energy photon beams, and the SAFs for the pregnant woman for photon energies above 50 keV are very similar between the two types of model. It is concluded that the use of tomographic models may not improve the operational radiation protection dosimetry involving photon exposures due to the large uncertainty already existed in the radiation protection quantities. It is also noted that the voxelized models have some major disadvantages and the radiation protection dosimetry community should consider hybrid approaches involving image-based voxels and advanced surface equations in the future.

关键词： Tomography

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Improved Monte Carlo adaptation of the heterogeneous coarse-mesh transport method

Improved Monte Carlo adaptation of the heterogeneous coarse-...

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Monte Carlo 2005 Topical Meeting

作者： Forget, Benoit Rahnema, Farzad Nuclear and Radiological Engineering / Medical Physics Program George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta GA 30332-0405

Recently, a coarse mesh transport method that couples Monte Carlo response function calculations to deterministic sweeps was extended to 2D (x,y) geometry. The deterministic sweeps were used to converge the partial currents on the coarse mesh boundaries while dealing with the statistical uncertainties in a straightforward fashion. The initial formulation used the cosine-current angular distribution and the spatially flat-flux approximation. This method yielded satisfactory results on the C5G7 MOX benchmark, but knowing that the cosine-current approximation breaks down near regions with strong absorption or in the vicinity of the coarse mesh corners, a new formulation was sought. The angular and spatial approximations were replaced by orthogonal polynomial expansions (Legendre polynomials) to develop a better representation of the partial currents connecting each coarse mesh. The method was then tested on two benchmark problems: a small 2D one group problem and the C5G7 MOX problem. In the first problem, using a 2nd order expansion in all variables (space, polar angle and azimuthal angle) with two segments per edge, we obtain an average pin power, a root mean square and a maximum errors of 0.09%, 0.11% and 0.18%, respectively. The eigenvalue of the coarse mesh method differs from the MCNP reference solution by -0.06%. In the C5G7 MOX benchmark problem, using 2nd polynomials expansions in all variables, the eigenvalue error is 0.06%. The average pin power, the root mean square and the maximum errors are 0.51%, 0.65% and 2.18%, respectively.

关键词： Monte Carlo methods

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Preliminary development of a 4D anatomical model for Monte Carlo simulations

Preliminary development of a 4D anatomical model for Monte C...

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Monte Carlo 2005 Topical Meeting

作者： Xu, X. George Shi, Chengyu Nuclear Engineering and Engineering Physics Program Rensselaer Polytechnic Institute Troy NY 12180 United States Department of Radiation Oncology University of Arkansas for Medical Sciences Little Rock AR 72205 United States

Existing anatomical models are mostly representative of three-dimensional (3D) standing individuals, based on either stylized surface equations (the so-called MIRD models) or tomographic images (the so-called voxel models). This paper presents a method to develop a 4D anatomical model using the existing 3D VIP-Man model, the Non-Uniform Rational B-Splines (NURBS) method and clinically obtained respiratory motion data. A lesion in the left lung is simulated to study how the organ motions may affect dose to the lesion. The procedure to simulate the 4D VIP-Man models for Monte Carlo simulations using EGS code is described. This preliminary study demonstrates that the motion of the organs can be modeled in the Monte Carlo code for more accurate dose calculations. Although the study was based on the VIP-Man images, the method can be extended to patient specific models constructed, for example, from multi-slice CT images.

关键词： Monte Carlo methods

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Exploration of mathematical methods for fine group reconstruction of the net leakage and flux in pebble bed reactors

Exploration of mathematical methods for fine group reconstru...

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2005 Winter Meeting - American nuclear Society

作者： Hudson, Nathanael Rahnema, Farzad Ougouag, Abderrafi M. Gougar, Hans D. Georgia Institute of Technology Nuclear and Radiological Engineering and Medical Physics Program Atlanta GA 30332-0425 United States Nuclear Engineering Design and Research Department MS-3885 P.O. Box 1625 Idaho Falls ID 83415-3885 United States

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Accuracy of MICROX-2 for PBR analysis using Monte Carlo technique

Accuracy of MICROX-2 for PBR analysis using Monte Carlo tech...

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Monte Carlo 2005 Topical Meeting

作者： Hudson, Nathanael Ilas, Germina Rahnema, Farzad Ougouag, Abderrafi Gougar, Hans Terry, William Mphahlele, Ramatsemela Nuclear and Radiological Engineering/ Medical Physics Program George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta GA 30332-0405 Idaho National Laboratory Idaho Falls Idaho 83415-3885 National Nuclear Regulator PO Box 7106 Centurion 0046 South Africa Oak Ridge National Laboratory Oak Ridge TN 37831-6172

One of the important issues in a nodal diffusion analysis of a PER core is the generation of accurate nodal constants. As compared to a light water reactor (LWR) lattice, in which the variation of the core properties in the axial direction is relatively weak and therefore a 2-D modeling appropriate, the calculation at the core sub-region level for a PER needs to account for the third spatial dimension because of the complex geometry (double heterogeneity) of packed arrangements of spherical pebbles. The purpose of the present work was to assess the capability of the MICROX-2 code to generate accurate nodal cross sections for PER lattices. This preliminary evaluation was based on comparison to a continuous-energy, doubly heterogeneous MCNP reference model. The terms of the comparison were the infinite medium multiplication factor, the few-group cell-homogenized total, capture and fission cross-sections, and the spectral indices. The principal phenomena covered by these choices pertain to resonance treatment and double heterogeneity. The models developed here do not attempt to evaluate the effect of packing randomness at either heterogeneity level. Such a study will be discussed elsewhere. The double heterogeneity of the lattice cell was fully modeled in the MCNP reference model. The cell-homogenized few-group cross sections and spectral parameters were calculated in MCNP by using the reaction rates and flux tallies. A spherical geometry model was used with MICROX-2. The analysis was completed at cold, room temperature (296 K) and at hot operating conditions (1073 K). For consistency, the same cross section data files were used for generating both the pointwise cross sections for MCNP and the fine-group cross sections for MICROX-2. Results showed significant differences between the MCNP and the MICROX-2 results, especially in the thermal and resonance energy range.

关键词： nuclear reactors

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Effect of fuel particles distribution model on PBR cell parameters

Effect of fuel particles distribution model on PBR cell para...

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2005 Annual Meeting - American nuclear Society

作者： Ilas, Germina Rahnema, Farzad Ougouag, Abderrafi M. Nuclear and Radiological Engineering/Medical Physics Program George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta GA 30332-0405 United States Idaho National Laboratory Idaho Falls ID 83415-3885 United States Oak Ridge National Laboratory Oak Ridge TN 37831-6172 United States

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An advanced ultrasonic technique for flow and void fraction measurements of two-phase flow

An advanced ultrasonic technique for flow and void fraction ...

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12th International Conference on nuclear engineering (ICONE12) - 2004

作者： Faccini, J.L.H. Harve, G.D. Su, J. Chang, J.S. Nuclear Engineering Institute CNEN Brazil Department of Engineering Physics McMaster University Canada Nuclear Engineering Program COPPE Federal University of Rio de Janeiro Brazil

In this paper, we present a hybrid type contrapropagating transmission ultrasonic technique (CPTU) for flow and time averaging ultrasonic transmission intensity void fraction measurements (TATIU) of air-water two-phase flow, which is tested in the new two-phase flow test section mounted recently onto an existing single phase flow rig at the nuclear engineering Institute (IEN)/CNEN, Brazil. The circular pipe test section is made of 51.2 mm stainless steel, followed by a transparent extruded acrylic pipe aimed at flow visualization. The two-phase flow rig operates in several flow regimes: bubbly, smooth stratified, wavy stratified and slug flow. The observed flow patterns are compared with the Mandhane et al.'s experimental and Lightstone et al.'s numerical flow regime map for horizontal two phase flows. These flow patterns will be identified by time averaging transmission intensity ultrasonic techniques which have been developed to meet this particular application. A contrapropagating transmission ultrasonic flowmeter is used to measure the flow rate of liquid phase. A pulse-echo TATIU ultrasonic technique used to measure the void fraction of the horizontal test section assembling at IEN is presented. Other flow parameters can be deduced by processing the signals obtained by the CPTU ultrasonic flowmeter and the pulse-echo generator-receiver (TATIU system).

关键词： Two phase flow

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