The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Jim M. Wild - One of the best experts on this subject based on the ideXlab platform.
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the influence of lung airways Branching Structure and diffusion time on measurements and models of short range 3he gas mr diffusion
Journal of Magnetic Resonance, 2012Co-Authors: Juan Parrarobles, Jim M. WildAbstract:Abstract Hyperpolarized 3 He diffusion experiments have been shown to be sensitive to changes in acinar Structure due to emphysematous lung disease. Extracting quantitative information about lung microStructure from the diffusion signal is complicated due its dependence on a number of factors including diffusion time and the complex Branching acinar geometry. A theoretical model (cylinder model) has been proposed as a means of estimating acinar airway dimensions from measured diffusivities. This model assumes that the effects of acinar Branching geometry and finite airway length upon 3 He diffusion behaviour are negligible. In this work, we use finite element simulations of diffusion in a model of Branching alveolar ducts to investigate in detail the effects of acinar Branching Structure and finite airway length on short-range 3 He diffusion measurements. The results show that Branching effects have a significant influence upon 3 He diffusivity, even at short diffusion times. The expressions of the cylinder model theory do not account for significant dependences upon diffusion time, Branching geometry and airway length, as a consequence of the oversimplified geometrical model used. The effect of diffusion time on 3 He ADC was also investigated through experiments with healthy human volunteers. The results demonstrate that the cylinder model can produce inaccurate estimates of the airway dimensions as a consequence of incompletely accounting for the diffusion-time dependence in the model equations and confirmed the predicted limitations of the cylinder model for reliable lung morphometry measurements. The results and models presented in this work may help in the development of a more realistic theoretical framework for ‘in vivo lung morphometry’ using 3 He diffusion MR.
Mark S Conradi - One of the best experts on this subject based on the ideXlab platform.
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commentary on the influence of lung airways Branching Structure and diffusion time on measurements and models of short range 3he gas mr diffusion
Journal of Magnetic Resonance, 2014Co-Authors: Dmitriy A Yablonskiy, Alexander L Sukstanskii, Mark S ConradiAbstract:In a recently published paper by Parra-Robles and Wild, the authors challenge the in vivo lung morphometry technique (based on hyperpolarized gas diffusion MRI) developed by our Washington University research group. In this Commentary we demonstrate that the main conclusion of Parra-Robles and Wild, that our MRI-based lung morphometry technique "produces inaccurate estimates of the airway dimensions", does not have any scientific basis and is not in agreement with the considerable body of peer-reviewed scientific reports as well as with Parra-Robles and Wild's own data. On the contrary, our technique has a strong theoretical background, is validated, and provides accurate 3D tomographic information on lung microstructural parameters previously available only from invasive biopsy specimens. This technique has already produced a number of results related to lung morphology and function that were not previously available. In our Commentary we also discuss a number of other incorrect statements in and shortcomings of Parra-Robles and Wild's paper.
Sh. Bolandi - One of the best experts on this subject based on the ideXlab platform.
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effect of Branching characteristics of ethylene 1 butene copolymers on melt flow index
Polymer Testing, 2006Co-Authors: Naghmeh Fazeli, H. Arabi, Sh. BolandiAbstract:Abstract Five different samples of ethylene/1-butene copolymers with relatively similar weight average molecular weight and molecular weight distribution, but different Branching characteristics, were investigated. The co-monomer content of the samples was measured by 13C NMR technique. Then, the samples were fractionated by a step-wise crystallization method in DSC and the relative amount of each fraction was compared between the samples. By measuring the Melt Flow Index (MFI) of the samples, a qualitative relationship between the Branching Structure and MFI of the samples is proposed.
Juan Parrarobles - One of the best experts on this subject based on the ideXlab platform.
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the influence of lung airways Branching Structure and diffusion time on measurements and models of short range 3he gas mr diffusion
Journal of Magnetic Resonance, 2012Co-Authors: Juan Parrarobles, Jim M. WildAbstract:Abstract Hyperpolarized 3 He diffusion experiments have been shown to be sensitive to changes in acinar Structure due to emphysematous lung disease. Extracting quantitative information about lung microStructure from the diffusion signal is complicated due its dependence on a number of factors including diffusion time and the complex Branching acinar geometry. A theoretical model (cylinder model) has been proposed as a means of estimating acinar airway dimensions from measured diffusivities. This model assumes that the effects of acinar Branching geometry and finite airway length upon 3 He diffusion behaviour are negligible. In this work, we use finite element simulations of diffusion in a model of Branching alveolar ducts to investigate in detail the effects of acinar Branching Structure and finite airway length on short-range 3 He diffusion measurements. The results show that Branching effects have a significant influence upon 3 He diffusivity, even at short diffusion times. The expressions of the cylinder model theory do not account for significant dependences upon diffusion time, Branching geometry and airway length, as a consequence of the oversimplified geometrical model used. The effect of diffusion time on 3 He ADC was also investigated through experiments with healthy human volunteers. The results demonstrate that the cylinder model can produce inaccurate estimates of the airway dimensions as a consequence of incompletely accounting for the diffusion-time dependence in the model equations and confirmed the predicted limitations of the cylinder model for reliable lung morphometry measurements. The results and models presented in this work may help in the development of a more realistic theoretical framework for ‘in vivo lung morphometry’ using 3 He diffusion MR.
Dmitriy A Yablonskiy - One of the best experts on this subject based on the ideXlab platform.
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commentary on the influence of lung airways Branching Structure and diffusion time on measurements and models of short range 3he gas mr diffusion
Journal of Magnetic Resonance, 2014Co-Authors: Dmitriy A Yablonskiy, Alexander L Sukstanskii, Mark S ConradiAbstract:In a recently published paper by Parra-Robles and Wild, the authors challenge the in vivo lung morphometry technique (based on hyperpolarized gas diffusion MRI) developed by our Washington University research group. In this Commentary we demonstrate that the main conclusion of Parra-Robles and Wild, that our MRI-based lung morphometry technique "produces inaccurate estimates of the airway dimensions", does not have any scientific basis and is not in agreement with the considerable body of peer-reviewed scientific reports as well as with Parra-Robles and Wild's own data. On the contrary, our technique has a strong theoretical background, is validated, and provides accurate 3D tomographic information on lung microstructural parameters previously available only from invasive biopsy specimens. This technique has already produced a number of results related to lung morphology and function that were not previously available. In our Commentary we also discuss a number of other incorrect statements in and shortcomings of Parra-Robles and Wild's paper.