The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform
Norbert J. Pelc - One of the best experts on this subject based on the ideXlab platform.
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The feasibility of an inverse geometry CT system with Stationary Source arrays.
Medical physics, 2013Co-Authors: Scott S. Hsieh, Joseph A. Heanue, Tobias Funk, Waldo Hinshaw, Brian P. Wilfley, Edward G. Solomon, Norbert J. PelcAbstract:Purpose: Inverse geometry computed tomography (IGCT) has been proposed as a new system architecture that combines a small detector with a large, distributed Source. This geometry can suppress cone-beam artifacts, reduce scatter, and increase dose efficiency. However, the temporal resolution of IGCT is still limited by the gantry rotation time. Large reductions in rotation time are in turn difficult due to the large Source array and associated power electronics. We examine the feasibility of using Stationary Source arrays for IGCT in order to achieve better temporal resolution. We anticipate that multiple Source arrays are necessary, with each Source array physically separated from adjacent ones. Methods: Key feasibility issues include spatial resolution, artifacts, flux, noise, collimation, and system timing clashes. The separation between the different Source arrays leads to missing views, complicating reconstruction. For the special case of three Source arrays, a two-stage reconstruction algorithm is used to estimate the missing views. Collimation is achieved using a rotating collimator with a small number of holes. A set of equally spaced Source spots are designated on the Source arrays, and a Source spot is energized when a collimator hole is aligned with it. System timing clashes occur when multiple Source spots are scheduled to be energized simultaneously. We examine flux considerations to evaluate whether sufficient flux is available for clinical applications. Results: The two-stage reconstruction algorithm suppresses cone-beam artifacts while maintaining resolution and noise characteristics comparable to standard third generation systems. The residual artifacts are much smaller in magnitude than the cone-beam artifacts eliminated. A mathematical condition is given relating collimator hole locations and the number of virtual Source spots for which system timing clashes are avoided. With optimization, sufficient flux may be achieved for many clinical applications. Conclusions: IGCT with Stationary Source arrays could be an imaging platform potentially capable of imaging a complete 16-cm thick volume within a tenth of a second.
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A volumetric reconstruction algorithm for Stationary Source inverse-geometry CT
Medical Imaging 2012: Physics of Medical Imaging, 2012Co-Authors: Scott S. Hsieh, Norbert J. PelcAbstract:Stationary Source inverse-geometry CT (SS-IGCT) has been proposed as a new system architecture that has several key advantages over traditional cone beam CT (CBCT). One advantage is the potential for acquiring a large volume of interest with minimal cone-beam artifacts and with very high temporal resolution. We anticipate that SS-IGCT will use large, Stationary Source arrays, with gaps in between separate Source array modules. These gaps make reconstruction challenging because most analytic reconstruction algorithms assume a continuous Source trajectory. SS-IGCT is capable of producing the same dataset as a traditional scanner taking multiple overlapping axial scans, but with segments of the views missing from each axial scan because of gaps. We propose the following, two-stage volumetric reconstruction algorithm. In the first stage, the missing rays are estimated in a spatially varying fashion using available data and geometric considerations, and reconstruction proceeds with standard algorithms. The missing data are then re-estimated by a forward projection step. These new estimates are quite good and the reconstruction can be performed again using any algorithm that supports multiple parallel axial scans. Although inspired by iterative reconstruction, our algorithm only needs one "iteration" of forward- and back-projection in practice and is efficient. Simulations of a thorax phantom were performed showing the efficacy of this technique and the ability of SS-IGCT to suppress cone-beam artifacts compared to conventional CBCT. The noise and resolution characteristics are comparable to that of CBCT.
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An inverse geometry CT system with Stationary Source arrays
Medical Imaging 2011: Physics of Medical Imaging, 2011Co-Authors: Scott S. Hsieh, Joseph A. Heanue, Tobias Funk, Waldo Hinshaw, Norbert J. PelcAbstract:Traditional CT systems face a tradeoff between temporal resolution, volumetric coverage and cone beam artifacts and also have limited ability to customize the distribution of incident x-rays to the imaging task. Inverse geometry CT (IGCT) can overcome some of these limitations by placing a small detector opposite a large, rotating scanned Source array. It is difficult to quickly rotate this Source array to achieve rapid imaging, so we propose using Stationary Source arrays instead and investigate the feasibility of such a system. We anticipate that distinct Source arrays will need to be physically separated, creating gaps in the sinogram. Symmetry can be used to fill the missing rays except those connecting gaps. With three Source arrays, a large triangular field of view emerges. As the small detector orbits the patient, each Source spot must be energized at multiple specifically designed times to ensure adequate sampling. A timing scheme is proposed that avoids timing clashes, efficiently uses the detector, and allows for simple collimation. The two-dimensional MTF, noise characteristics, and artifact levels are all found to be comparable to parallel-beam systems. A complete, 100 millisecond volumetric scan may be feasible.
Thomas J Butler - One of the best experts on this subject based on the ideXlab platform.
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response of ozone and nitrate to Stationary Source nox emission reductions in the eastern usa
Atmospheric Environment, 2011Co-Authors: Thomas J Butler, Francoise Vermeylen, Melissa Rury, Gene E Likens, Brian Lee, George E Bowker, Lance MccluneyAbstract:Abstract This study is an assessment of the impact of reduced Stationary Source NO x emissions on ground-level concentrations of ozone (O 3 ) and dry-NO 3 (HNO 3(g) + NO 3 − (p) ) in the eastern United States (EUS). Total anthropogenic NO x and VOC emissions have declined 32% and 20%, respectively, from 1997 to 2005 in the 20 eastern states participating in a NO x Budget Trading Program (NBP). Annual and ozone season (OS) NO x emissions from electric generating units (EGUs) have declined 48% and 66%, respectively, in the EUS. From 1997–1999 to 2006–2008 measured decline in meteorologically adjusted (met-adj) daily maximum 8-h (dm8h) O 3 , has been 8 ppb or 14% for the EUS during the May–September OS, with the largest declines occurring in the highest concentration category (99th percentile). Random coefficient models, with NBP and Acid Rain Program (ARP) regulated NO x emissions as the independent variable, show highly significant relations ( p ≤ 0.0001) to dm8h O 3 for 1997–2008 during the OS. Regional declines within the EUS range from 11% to 16%. The patterns of the O 3 trends are in general agreement with other recent studies. Rural and urban sites both show similar levels of decline from pre- to post-NBP periods. Dry-NO 3 during the OS shows a substantial decline from 3.1 to 1.8 μg NO 3 m −3 . Random coefficient models show regional results ranging from 32% to 39% declines, and measured results show a 35–46% decline in dry-NO 3 from 1997–1999 to 2006–2008. These results suggest that regulating NO x emissions has been highly effective in reducing both ozone and dry-NO 3 concentrations during the OS. Overall, a 32% reduction in total annual anthropogenic NO x emissions from 1997 to 2005 has been accompanied by a 7–8 ppb, or 12–13% decline in OS dm8h O 3 concentration, and a 34% decline in dry-NO 3 concentration in the 20-state NBP region. Model results indicate a 50% further reduction in NBP regulated NO x emissions will reduce O 3 concentrations an additional 3–5% and dry-NO 3 concentrations by 13–16%.
Farshad Lahouti - One of the best experts on this subject based on the ideXlab platform.
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distortion power tradeoffs in quasi Stationary Source transmission over delay and buffer limited block fading channels
IEEE Transactions on Wireless Communications, 2016Co-Authors: Roghayeh Joda, Farshad Lahouti, Elza ErkipAbstract:This paper investigates distortion-power tradeoffs in transmission of quasi-Stationary Sources over delay and buffer limited block fading channels by studying encoder and decoder buffering techniques to smooth out the Source and channel variations. Four Source and channel coding schemes that consider buffer and power constraints are presented to minimize the reconstructed Source distortion. The first one is a high performance scheme, which benefits from optimized Source and channel rate adaptation. In the second scheme, the channel coding rate is fixed and optimized along with transmission power with respect to channel and Source variations; hence this scheme enjoys simplicity of implementation. The two last schemes have fixed transmission power with optimized adaptive or fixed channel coding rate. For all the proposed schemes, closed form solutions for mean distortion, optimized rate, and power are provided and in the high SNR regime, the mean distortion exponent and the asymptotic mean power gains are derived. The proposed schemes with buffering exploit the diversity due to Source and channel variations. Specifically, when the buffer size is limited, fixed channel rate adaptive power scheme outperforms an adaptive rate fixed power scheme. Furthermore, analytical and numerical results demonstrate that with limited buffer size, the system performance in terms of reconstructed signal SNR saturates as transmission power increases, suggesting that appropriate buffer size selection is important to achieve a desired reconstruction quality.
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Delay-Limited Source and Channel Coding of Quasi-Stationary Sources over Block Fading Channels: Design and Scaling Laws
IEEE Transactions on Communications, 2013Co-Authors: Roghayeh Joda, Farshad LahoutiAbstract:In this paper, delay-limited transmission of quasi-Stationary Sources over block fading channels is considered. Considering distortion outage probability as the performance measure, two Source and channel coding schemes with power adaptive transmission are presented. The first one is optimized for fixed rate transmission, and hence enjoys simplicity of implementation. The second one is a high performance scheme, which also benefits from optimized rate adaptation with respect to Source and channel states. In high SNR regime, the performance scaling laws in terms of outage distortion exponent and asymptotic outage distortion gain are derived, where two schemes with fixed transmission power and adaptive or optimized fixed rates are considered as benchmarks for comparisons. Various analytical and numerical results are provided which demonstrate a superior performance for Source and channel optimized rate and power adaptive scheme. It is also observed that from a distortion outage perspective, the fixed rate adaptive power scheme substantially outperforms an adaptive rate fixed power scheme for delay-limited transmission of quasi-Stationary Sources over wireless block fading channels. The effect of the characteristics of the quasi-Stationary Source on performance, and the implication of the results for transmission of Stationary Sources are also investigated.
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Delay-limited Source and Channel Coding of Quasi-Stationary Sources over Block Fading Channels: Design and Scaling Laws
arXiv: Information Theory, 2012Co-Authors: Roghayeh Joda, Farshad LahoutiAbstract:In this paper, delay-limited transmission of quasi-Stationary Sources over block fading channels are considered. Considering distortion outage probability as the performance measure, two Source and channel coding schemes with power adaptive transmission are presented. The first one is optimized for fixed rate transmission, and hence enjoys simplicity of implementation. The second one is a high performance scheme, which also benefits from optimized rate adaptation with respect to Source and channel states. In high SNR regime, the performance scaling laws in terms of outage distortion exponent and asymptotic outage distortion gain are derived, where two schemes with fixed transmission power and adaptive or optimized fixed rates are considered as benchmarks for comparisons. Various analytical and numerical results are provided which demonstrate a superior performance for Source and channel optimized rate and power adaptive scheme. It is also observed that from a distortion outage perspective, the fixed rate adaptive power scheme substantially outperforms an adaptive rate fixed power scheme for delay-limited transmission of quasi-Stationary Sources over wireless block fading channels. The effect of the characteristics of the quasi-Stationary Source on performance, and the implication of the results for transmission of Stationary Sources are also investigated.
Lance Mccluney - One of the best experts on this subject based on the ideXlab platform.
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response of ozone and nitrate to Stationary Source nox emission reductions in the eastern usa
Atmospheric Environment, 2011Co-Authors: Thomas J Butler, Francoise Vermeylen, Melissa Rury, Gene E Likens, Brian Lee, George E Bowker, Lance MccluneyAbstract:Abstract This study is an assessment of the impact of reduced Stationary Source NO x emissions on ground-level concentrations of ozone (O 3 ) and dry-NO 3 (HNO 3(g) + NO 3 − (p) ) in the eastern United States (EUS). Total anthropogenic NO x and VOC emissions have declined 32% and 20%, respectively, from 1997 to 2005 in the 20 eastern states participating in a NO x Budget Trading Program (NBP). Annual and ozone season (OS) NO x emissions from electric generating units (EGUs) have declined 48% and 66%, respectively, in the EUS. From 1997–1999 to 2006–2008 measured decline in meteorologically adjusted (met-adj) daily maximum 8-h (dm8h) O 3 , has been 8 ppb or 14% for the EUS during the May–September OS, with the largest declines occurring in the highest concentration category (99th percentile). Random coefficient models, with NBP and Acid Rain Program (ARP) regulated NO x emissions as the independent variable, show highly significant relations ( p ≤ 0.0001) to dm8h O 3 for 1997–2008 during the OS. Regional declines within the EUS range from 11% to 16%. The patterns of the O 3 trends are in general agreement with other recent studies. Rural and urban sites both show similar levels of decline from pre- to post-NBP periods. Dry-NO 3 during the OS shows a substantial decline from 3.1 to 1.8 μg NO 3 m −3 . Random coefficient models show regional results ranging from 32% to 39% declines, and measured results show a 35–46% decline in dry-NO 3 from 1997–1999 to 2006–2008. These results suggest that regulating NO x emissions has been highly effective in reducing both ozone and dry-NO 3 concentrations during the OS. Overall, a 32% reduction in total annual anthropogenic NO x emissions from 1997 to 2005 has been accompanied by a 7–8 ppb, or 12–13% decline in OS dm8h O 3 concentration, and a 34% decline in dry-NO 3 concentration in the 20-state NBP region. Model results indicate a 50% further reduction in NBP regulated NO x emissions will reduce O 3 concentrations an additional 3–5% and dry-NO 3 concentrations by 13–16%.
Roghayeh Joda - One of the best experts on this subject based on the ideXlab platform.
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distortion power tradeoffs in quasi Stationary Source transmission over delay and buffer limited block fading channels
IEEE Transactions on Wireless Communications, 2016Co-Authors: Roghayeh Joda, Farshad Lahouti, Elza ErkipAbstract:This paper investigates distortion-power tradeoffs in transmission of quasi-Stationary Sources over delay and buffer limited block fading channels by studying encoder and decoder buffering techniques to smooth out the Source and channel variations. Four Source and channel coding schemes that consider buffer and power constraints are presented to minimize the reconstructed Source distortion. The first one is a high performance scheme, which benefits from optimized Source and channel rate adaptation. In the second scheme, the channel coding rate is fixed and optimized along with transmission power with respect to channel and Source variations; hence this scheme enjoys simplicity of implementation. The two last schemes have fixed transmission power with optimized adaptive or fixed channel coding rate. For all the proposed schemes, closed form solutions for mean distortion, optimized rate, and power are provided and in the high SNR regime, the mean distortion exponent and the asymptotic mean power gains are derived. The proposed schemes with buffering exploit the diversity due to Source and channel variations. Specifically, when the buffer size is limited, fixed channel rate adaptive power scheme outperforms an adaptive rate fixed power scheme. Furthermore, analytical and numerical results demonstrate that with limited buffer size, the system performance in terms of reconstructed signal SNR saturates as transmission power increases, suggesting that appropriate buffer size selection is important to achieve a desired reconstruction quality.
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Delay-Limited Source and Channel Coding of Quasi-Stationary Sources over Block Fading Channels: Design and Scaling Laws
IEEE Transactions on Communications, 2013Co-Authors: Roghayeh Joda, Farshad LahoutiAbstract:In this paper, delay-limited transmission of quasi-Stationary Sources over block fading channels is considered. Considering distortion outage probability as the performance measure, two Source and channel coding schemes with power adaptive transmission are presented. The first one is optimized for fixed rate transmission, and hence enjoys simplicity of implementation. The second one is a high performance scheme, which also benefits from optimized rate adaptation with respect to Source and channel states. In high SNR regime, the performance scaling laws in terms of outage distortion exponent and asymptotic outage distortion gain are derived, where two schemes with fixed transmission power and adaptive or optimized fixed rates are considered as benchmarks for comparisons. Various analytical and numerical results are provided which demonstrate a superior performance for Source and channel optimized rate and power adaptive scheme. It is also observed that from a distortion outage perspective, the fixed rate adaptive power scheme substantially outperforms an adaptive rate fixed power scheme for delay-limited transmission of quasi-Stationary Sources over wireless block fading channels. The effect of the characteristics of the quasi-Stationary Source on performance, and the implication of the results for transmission of Stationary Sources are also investigated.
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Delay-limited Source and Channel Coding of Quasi-Stationary Sources over Block Fading Channels: Design and Scaling Laws
arXiv: Information Theory, 2012Co-Authors: Roghayeh Joda, Farshad LahoutiAbstract:In this paper, delay-limited transmission of quasi-Stationary Sources over block fading channels are considered. Considering distortion outage probability as the performance measure, two Source and channel coding schemes with power adaptive transmission are presented. The first one is optimized for fixed rate transmission, and hence enjoys simplicity of implementation. The second one is a high performance scheme, which also benefits from optimized rate adaptation with respect to Source and channel states. In high SNR regime, the performance scaling laws in terms of outage distortion exponent and asymptotic outage distortion gain are derived, where two schemes with fixed transmission power and adaptive or optimized fixed rates are considered as benchmarks for comparisons. Various analytical and numerical results are provided which demonstrate a superior performance for Source and channel optimized rate and power adaptive scheme. It is also observed that from a distortion outage perspective, the fixed rate adaptive power scheme substantially outperforms an adaptive rate fixed power scheme for delay-limited transmission of quasi-Stationary Sources over wireless block fading channels. The effect of the characteristics of the quasi-Stationary Source on performance, and the implication of the results for transmission of Stationary Sources are also investigated.
