The Experts below are selected from a list of 458607 Experts worldwide ranked by ideXlab platform
Charles C. Watson - One of the best experts on this subject based on the ideXlab platform.
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completion of a truncated attenuation image from the attenuated pet Emission Data
IEEE Transactions on Medical Imaging, 2013Co-Authors: Johan Nuyts, Christian Michel, Matthias Fenchel, Girish Bal, Frank Kehren, Charles C. WatsonAbstract:Positron Emission tomographs (PETs) are currently almost exclusively designed as hybrid systems. The current standard is the PET/CT combination, while prototype PET/MRI systems are being studied by several research groups. One problem in these systems is that the transaxial field-of-view of the second system is smaller than that of the PET camera and does not provide complete attenuation Data. Because this second system provides the image for PET attenuation and scatter correction, the smaller FOV causes truncation of the attenuation map, producing bias in the attenuation corrected activity image. In this paper, we propose a maximum-a-posteriori algorithm for estimating the missing part of the attenuation map from the PET Emission Data. The method is evaluated on five artificially truncated 18F-FDG PET/CT studies, where it reduced the error on the reconstructed PET activities from 20% to less than 7%. The results on a PET/MRI patient study with 18F-FDG are presented as well.
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Completion of a truncated attenuation image from the attenuated PET Emission Data
IEEE Transactions on Medical Imaging, 2012Co-Authors: Johan Nuyts, Christian Michel, Matthias Fenchel, Charles C. WatsonAbstract:Positron Emission tomographs (PET) are currently almost exclusively designed as hybrid systems. The current standard is the PET/CT combination, while prototype PET/MRI systems are being studied by several research groups. One problem in these systems is that the transaxial field of view of the second system is smaller than that of the PET camera. The problem is limited for PET/CT, it is more pronounced in PET/MRI. Because this second system provides the image for attenuation correction, the smaller field of view causes truncation of the attenuation map. In this paper, we propose a maximum-a-posteriori algorithm for estimating the missing part of the attenuation map from the PET Emission Data.
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Scatter/trues detection efficiency compensation in scatter correction of PET Emission Data
2008 IEEE Nuclear Science Symposium Conference Record, 2008Co-Authors: Charles C. Watson, Christian Michel, Larry Byars, H. RothfussAbstract:In positron Emission tomography (PET), a detector’s response to scattered radiation may be different from its response to unscattered (true coincidence) photons. This difference should be accounted for during normalization and scatter correction. We show that only a knowledge of the ratio of the scatter to trues efficiencies is necessary, however. We describe a new technique for measuring the scatter/trues detection efficiency ratio, and a procedure for applying this compensation during the scatter correction of PET Emission Data. We present some initial results, confirmed by simulations, indicating that the scatter/trues efficiencies may vary by up to 20% for a Siemens BrainPET MR insert in the vicinity of block gaps near the center of the transaxial field of view. These variations could result in ±5% variations in scatter corrected images if left uncompensated.
Johan Nuyts - One of the best experts on this subject based on the ideXlab platform.
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completion of a truncated attenuation image from the attenuated pet Emission Data
IEEE Transactions on Medical Imaging, 2013Co-Authors: Johan Nuyts, Christian Michel, Matthias Fenchel, Girish Bal, Frank Kehren, Charles C. WatsonAbstract:Positron Emission tomographs (PETs) are currently almost exclusively designed as hybrid systems. The current standard is the PET/CT combination, while prototype PET/MRI systems are being studied by several research groups. One problem in these systems is that the transaxial field-of-view of the second system is smaller than that of the PET camera and does not provide complete attenuation Data. Because this second system provides the image for PET attenuation and scatter correction, the smaller FOV causes truncation of the attenuation map, producing bias in the attenuation corrected activity image. In this paper, we propose a maximum-a-posteriori algorithm for estimating the missing part of the attenuation map from the PET Emission Data. The method is evaluated on five artificially truncated 18F-FDG PET/CT studies, where it reduced the error on the reconstructed PET activities from 20% to less than 7%. The results on a PET/MRI patient study with 18F-FDG are presented as well.
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Completion of a truncated attenuation image from the attenuated PET Emission Data
IEEE Transactions on Medical Imaging, 2012Co-Authors: Johan Nuyts, Christian Michel, Matthias Fenchel, Charles C. WatsonAbstract:Positron Emission tomographs (PET) are currently almost exclusively designed as hybrid systems. The current standard is the PET/CT combination, while prototype PET/MRI systems are being studied by several research groups. One problem in these systems is that the transaxial field of view of the second system is smaller than that of the PET camera. The problem is limited for PET/CT, it is more pronounced in PET/MRI. Because this second system provides the image for attenuation correction, the smaller field of view causes truncation of the attenuation map. In this paper, we propose a maximum-a-posteriori algorithm for estimating the missing part of the attenuation map from the PET Emission Data.
Gengsheng L. Zeng - One of the best experts on this subject based on the ideXlab platform.
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Modification of Green's one-step-late algorithm for attenuated Emission Data.
Biomedical physics & engineering express, 2019Co-Authors: Gengsheng L. ZengAbstract:Green's one-step-late (OSL) algorithm is a popular image reconstruction algorithm in Emission-Data tomography, in spite of its convergence issues. One drawback of Green's algorithm is that the algorithm exhibits non-stationary regularization when the algorithm's projector and backprojector model the attenuation effects in single photon Emission computed tomography (SPECT). This paper suggests a remedy to improve Green's OSL algorithm so that stationary regularization can be obtained. This paper also observes some similarities between the modified Green's OSL algorithm and the gradient descent algorithm.
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SPECT region of interest reconstruction with truncated transmission and Emission Data.
Medical physics, 2010Co-Authors: Gengsheng L. Zeng, Grant T. GullbergAbstract:Purpose: The aim of this article is to propose an exact SPECT region of interest (ROI) reconstruction method using truncated transmission and truncated Emission Data. Methods: Recently, the authors published two articles in Physics in Medicine and Biology with two results in SPECT ROI Emission image reconstruction. The first result states that if the transmission Data are truncated but the Emission Data are not truncated, the Emission image can be exactly reconstructed, provided the entire Emission image is inside the region where the transmission Data are not truncated. The second result states that if the transmission Data are not truncated, the Emission ROI can be exactly reconstructed with truncated Emission Data. This article combines these two results and obtains a new result that the Emission ROI can be exactly reconstructed if both transmission and Emission Data are truncated. Results: Computer simulations are performed to verify the proposed ROI image reconstruction algorithm. Conclusions: Exact SPECT ROI image reconstruction is possible using truncated transmission and Emission projections with some prior information about the attenuator and the Emission distribution.
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Attenuation map estimation with SPECT Emission Data only
International Journal of Imaging Systems and Technology, 2009Co-Authors: Yan Yan, Gengsheng L. ZengAbstract:Quantitative single-photon Emission computed tomography can be well achieved if photon attenuation is taken into account in the reconstruction process. Using a transmission scan is a common approach. A dramatic simplification could be made if the attenuation map could be obtained from the Emission Data. In this article, we propose a new method to estimate the attenuation map using the Data consistency conditions of the attenuated Radon transform. It is based on deriving boundaries of the constant regions of the true attenuation map using an iterative algorithm. This new method is tested by Monte Carlo simulations with the attenuation and scattering effects. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 271–276, 2009
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A method of attenuation map and Emission activity reconstructions from Emission Data
IEEE Transactions on Nuclear Science, 2001Co-Authors: Vladimir Y. Panin, Gengsheng L. Zeng, Grant T. GullbergAbstract:An iterative algorithm that reconstructs the attenuation map and Emission activity distribution from SPECT Emission Data is proposed. The algorithm is based on the quasilinearized attenuated Radon transform. At each iteration of the algorithm, Emission activity distribution is reconstructed using the attenuation map from the previous iteration. Then, the attenuation map is estimated by using the current Emission image. To effectively locate the attenuation map within a possible class of solutions the attenuation map is constrained by an optimal basis set, which is derived from a cross-correlation of a priori images known as a "knowledge set." Computer simulations show that the proposed algorithm has the capability to reconstruct the Emission activity distribution and the transmission map without the use of transmission measurements. The proposed method has been tested using clinically acquired Data.
Rainer Friedrich - One of the best experts on this subject based on the ideXlab platform.
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Comparison of measured and calculated motorway Emission Data
Atmospheric Environment, 2000Co-Authors: Bernhard Vogel, Rainer Friedrich, Ulrich Corsmeier, Heike Vogel, Franz Fiedler, J. Kühlwein, Andreas Obermeier, J. Weppner, Norbert Kalthoff, D. BäumerAbstract:Abstract A comprehensive field campaign was carried out to check the quality of modelled on-road Emissions of NOx and CO by comparing them with real-world Emissions on a motorway in the southwestern part of Germany. Three different sets of Emission Data were determined for a section of the motorway A 656 that connects Mannheim and Heidelberg. First, Emission Data were pre-calculated, that means before the field campaign took place, using literature Data for traffic volume, types of vehicles and driving speeds. Second, detailed traffic measurements during two intensive measurement phases were used to calculate improved Emission Data based on the actual traffic situation. Third, real-world Emission Data were determined by meteorological and chemical measurements. It shows that the differences of the pre-calculated Emission Data and the Emission Data improved by the traffic measurements differ by less than 15% in case of CO and approx. by 35% in case of NOx. A comparison of the observed Emissions with the calculated ones gives an agreement for NOx within the error bars. For CO, however, a discrepancy by a factor of two was found. The real-world Emissions were much higher than calculated.
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GENEMIS: Generation of European Emission Data for Episodes
Transport and Chemical Transformation of Pollutants in the Troposphere, 2000Co-Authors: Rainer FriedrichAbstract:For the analysis of atmospheric processes and the application and evaluation of atmospheric models, reliable Emission Data with high temporal and spatial resolution are needed. Within the GENEMIS subproject, such Data have been generated. To achieve a high temporal resolution, the processes that cause the Emissions have been analysed, and parameters which can be used to describe the temporal variation of the underlying activities have been identified and used to describe the temporal course of the Emissions. It was shown that strong variations of Emissions with time occur. For example. Emissions are approximately 30 % lower on weekend days than during working days. Also. the ratio between anthropogenic VOC and NOx Emissions is higher during the day than in the night. furthermore it is much higher in urban than in rural areas. Progress was also achieved in estimating NH3 Emissions and their temporal distribution. Another achievement is the development of methods for updating annual inventories. Know-how from national experts of several countries contributed to improve the Database, especially for central and eastern Europe. In an experiment at the Gubrist tunnel in Switzerland, measurements of the concentrations of pollutants at the entrance and the exit of the tunnel were made to derive the Emissions in the tunnel. The resulting Emissions were compared to the calculated Emissions. A good agreement between measurements and calculated Emissions could be shown for gasoline cars.
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CAREAIR: A Computer Aided Modeling Toolbox to Generate and Analyze Emission Data in High Temporal and Spatial Resolution
Journal of the Air & Waste Management Association (1995), 1998Co-Authors: Richard K. Laing, Burkhard Wickert, Rainer FriedrichAbstract:For the evaluation of air quality improvement strategies, Emission Data in high temporal and spatial resolution is necessary, including all Emission sources and all relevant pollutant species. Computer aided models are usually used to generate this Emission Data because it is not possible to obtain measurements from all sources, and, furthermore, a large amount of Data has to be handled. For the development of Emission modeling systems, a software tool called CAREAIR has been created. The intention of this paper is to introduce CAREAIR to the international community dealing with Emission inventories and air quality improvement strategies. CAREAIR is not just a single Emission model but a flexible modeling toolbox. The Database contains Data and formulas for Data manipulation, which is performed by using a set of flexible operators with different specifications. The Emission calculation is carried out by combining several Data manipulation operators. The CAREAIR modeling toolbox allows model implementation for the calculation of Emissions from different pollutants in a high spatial and temporal resolution. The application of CAREAIR within various investigation projects in Germany, Europe, and Nigeria shows that CAREAIR is an appropriate instrument for the development of flexible Emission models by meeting the various demands of these projects. The function and the Data structures of this modeling toolbox are described and, towards the end of the paper, an example of an Emission calculation with CAREAIR is given.
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Temporal Disaggregation of Emission Data
Tropospheric Modelling and Emission Estimation, 1997Co-Authors: L. Lenhart, T. Heck, Rainer Friedrich, Dirk Adolph, Ulf Hansen, Jae-geung Kim, Burkhard Zinzius, Wilfried Winiwarter, Willem A.h. Asman, H. NielsenAbstract:For the investigation of transport and chemical transformation of pollutants with atmospheric models reliable Emission Data with high temporal and spatial resolution are required. Within the GENEMIS project methods have been developed to generate such Data, based on a thorough analysis of the processes, that cause the Emissions. Socio-economic, statistical and meteorological Data are used for the temporal and spatial disaggregation and the update of Emission Data. Results indicate a rather strong temporal and spatial variation of Emissions in Europe.
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European Emission Data with high temporal and spatial resolution
Water Air & Soil Pollution, 1995Co-Authors: L. Lenhart, Rainer FriedrichAbstract:The estimation of acidic deposition strongly depends on the availability of accurate Emission Data. The atmospheric models, that calculate concentrations and depositions of pollutants, need Data in a high temporal resolution (e.g. daily, 6-hourly or even hourly Data). However, although some progress has been achieved concerning annual Emission Data for Europe (e.g. CORINAIR 90), only very little information is available about the temporal variation of these Emissions during a year. Therefore, within the EUROTRAC-GENEMIS project special emphasis was laid on the development of methods to generate Emissions with a high temporal and spatial resolution. As results the temporal and spatial distribution of SO 2 -and NO x -Emissions are shown. The results indicate, that the Emissions vary considerably over time and that the use of simple patterns for the temporal disaggregation is not sufficient for modelling and assessment of acidic deposition.
Grant T. Gullberg - One of the best experts on this subject based on the ideXlab platform.
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SPECT region of interest reconstruction with truncated transmission and Emission Data.
Medical physics, 2010Co-Authors: Gengsheng L. Zeng, Grant T. GullbergAbstract:Purpose: The aim of this article is to propose an exact SPECT region of interest (ROI) reconstruction method using truncated transmission and truncated Emission Data. Methods: Recently, the authors published two articles in Physics in Medicine and Biology with two results in SPECT ROI Emission image reconstruction. The first result states that if the transmission Data are truncated but the Emission Data are not truncated, the Emission image can be exactly reconstructed, provided the entire Emission image is inside the region where the transmission Data are not truncated. The second result states that if the transmission Data are not truncated, the Emission ROI can be exactly reconstructed with truncated Emission Data. This article combines these two results and obtains a new result that the Emission ROI can be exactly reconstructed if both transmission and Emission Data are truncated. Results: Computer simulations are performed to verify the proposed ROI image reconstruction algorithm. Conclusions: Exact SPECT ROI image reconstruction is possible using truncated transmission and Emission projections with some prior information about the attenuator and the Emission distribution.
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A method of attenuation map and Emission activity reconstructions from Emission Data
IEEE Transactions on Nuclear Science, 2001Co-Authors: Vladimir Y. Panin, Gengsheng L. Zeng, Grant T. GullbergAbstract:An iterative algorithm that reconstructs the attenuation map and Emission activity distribution from SPECT Emission Data is proposed. The algorithm is based on the quasilinearized attenuated Radon transform. At each iteration of the algorithm, Emission activity distribution is reconstructed using the attenuation map from the previous iteration. Then, the attenuation map is estimated by using the current Emission image. To effectively locate the attenuation map within a possible class of solutions the attenuation map is constrained by an optimal basis set, which is derived from a cross-correlation of a priori images known as a "knowledge set." Computer simulations show that the proposed algorithm has the capability to reconstruct the Emission activity distribution and the transmission map without the use of transmission measurements. The proposed method has been tested using clinically acquired Data.