The Experts below are selected from a list of 150984 Experts worldwide ranked by ideXlab platform
M. Koch - One of the best experts on this subject based on the ideXlab platform.
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highly accurate optical Material Parameter determination with thz time domain spectroscopy
Optics Express, 2007Co-Authors: Ioachim Pupeza, Rafal Wilk, M. KochAbstract:We improve the existing data extraction algorithms for THz time-domain spectroscopy (THz TDS) in two aspects. On the one hand, we merge the up-to-date knowledge of THz TDS signal processing into a single powerful optical Material Parameter extraction algorithm. On the other hand, we introduce a novel iterative algorithm that further enhances the accuracy of the Parameter extraction. In contrast to most of the published experiments, we are able to reliably investigate samples with thicknesses as small as 100μm, samples with low indexes of refraction, i.e. close to 1, as well as samples with sharp peaks in the Material Parameter curves.
Nic Smith - One of the best experts on this subject based on the ideXlab platform.
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myocardial transversely isotropic Material Parameter estimation from in silico measurements based on a reduced order unscented kalman filter
Journal of The Mechanical Behavior of Biomedical Materials, 2011Co-Authors: Pablo Lamata, Jack Lee, Philippe Moireau, Dominique Chapelle, Nic SmithAbstract:Abstract Parameter estimation from non-invasive measurements is a crucial step in patient-specific cardiac modeling. It also has the potential to provide significant assistance in the clinical diagnosis of cardiac diseases through the quantification of myocardial Material heterogeneity. In this paper, we formulate a novel Reduced-order Unscented Kalman Filter (rUKF) applied to the left ventricular (LV) nonlinear mechanical model based on cubic-Hermite finite elements. Material Parameters in the widely-employed transversely isotropic Guccione’s constitutive law are successfully identified for both homogeneous and heterogeneous cases. We conclude that the four Parameters in Guccione’s law can be uniquely and correctly determined in-silico from noisy displacement measurements of Material points located on the myocardial surfaces. The future application of this novel and effective approach to real clinical measurements is thus promising.
Peter Hunter - One of the best experts on this subject based on the ideXlab platform.
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myocardial Material Parameter estimation a non homogeneous finite element study from simple shear tests
Biomechanics and Modeling in Mechanobiology, 2008Co-Authors: H. Schmid, Martyn P. Nash, P Ocallaghan, W L Lin, Ian J Legrice, Bruce H Smaill, Aa Young, Peter HunterAbstract:The passive Material properties of myocardium play a major role in diastolic performance of the heart. In particular, the shear behaviour is thought to play an important mechanical role due to the laminar architecture of myocardium. We have previously compared a number of myocardial constitutive relations with the aim to extract their suitability for inverse Material Parameter estimation. The previous study assumed a homogeneous deformation. In the present study we relaxed the homogeneous assumption by implementing these laws into a finite element environment in order to obtain more realistic measures for the suitability of these laws in both their ability to fit a given set of experimental data, as well as their stability in the finite element environment. In particular, we examined five constitutive laws and compare them on the basis of (i) “goodness of fit”: how well they fit a set of six shear deformation tests, (ii) “determinability”: how well determined the objective function is at the optimal Parameter fit, and (iii) “variability”: how well determined the Material Parameters are over the range of experiments. Furthermore, we compared the FE results with those from the previous study. It was found that the same Material law as in the previous study, the orthotropic Fung-type “Costa-Law”, was the most suitable for inverse Material Parameter estimation for myocardium in simple shear.
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myocardial Material Parameter estimation a comparative study for simple shear
Journal of Biomechanical Engineering-transactions of The Asme, 2006Co-Authors: H. Schmid, Martyn P. Nash, Alistair A. Young, Peter HunterAbstract:The study of ventricular mechanics-analyzing the distribution of strain and stress in myocardium throughout the cardiac cycle-is crucially dependent on the accuracy of the constitutive law chosen to represent the highly nonlinear and anisotropic properties of passive cardiac muscle. A number of such laws have been proposed and fitted to experimental measurements of stress-strain behavior. Here we examine five of these laws and compare them on the basis of (i) "goodness of fit:" How well they fit a set of six shear deformation tests, (ii) "determinability:" How well determined the objective function is at the optimal Parameter fit, and (iii) "variability:" How well determined the Material Parameters are over the range of experiments. These criteria are utilized to discuss the advantages and disadvantages of the constitutive laws.
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A computationally efficient optimization kernel for Material Parameter estimation procedures.
Journal of biomechanical engineering, 2006Co-Authors: H. Schmid, Martyn P. Nash, Alistair A. Young, Oliver Röhrle, Peter HunterAbstract:Estimating Material Parameters is an important part in the study of soft tissue mechanics. Computational time can easily run to days, especially when all available experimental data are taken into account. The Material Parameter estimation procedure is ex-amplified on a set of homogeneous simple shear experiments to estimate the orthotropic constitutive Parameters of myocardium. The modification consists of changing the traditional least-squares approach to a weighted least-squares. This objective function resembles a L 2 -norm type integral which is approximated using Gaussian quadrature. This reduces the computational time of the Material Parameter estimation by two orders of magnitude.
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ventricular mechanics in diastole Material Parameter sensitivity
Journal of Biomechanics, 2003Co-Authors: Carey Stevens, Ian J Legrice, E W Remme, Peter HunterAbstract:Models of ventricular mechanics have been developed over the last 20 years to include finite deformation theory, anisotropic and inhomogeneous Material properties and an accurate representation of ventricular geometry. As computer performance and the computational efficiency of the models improve, clinical application of these heart mechanics models is becoming feasible. One such application is to estimate myocardial Material properties by adjusting the constitutive Parameters to match wall deformation from MRI or ultrasound measurements, together with a measurement (or estimate) of ventricular pressure. Pigs are now the principal large animal model for these studies and in this paper we present the development of a new three-dimensional finite element model of the heart based on measurements of the geometry and the fibre and sheet orientations of pig hearts. The end-diastolic deformation of the model is computed using the "pole-zero" constitutive law which we have previously used to model the mechanics of passive myocardial tissue specimens. The sensitivities of end-diastolic fibre-sheet Material strains and heart shape to changes in the Material Parameters are computed for the Parameters of the pole-zero law in order to assess the utility of the models for inverse Material property determination.
Ioachim Pupeza - One of the best experts on this subject based on the ideXlab platform.
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highly accurate optical Material Parameter determination with thz time domain spectroscopy
Optics Express, 2007Co-Authors: Ioachim Pupeza, Rafal Wilk, M. KochAbstract:We improve the existing data extraction algorithms for THz time-domain spectroscopy (THz TDS) in two aspects. On the one hand, we merge the up-to-date knowledge of THz TDS signal processing into a single powerful optical Material Parameter extraction algorithm. On the other hand, we introduce a novel iterative algorithm that further enhances the accuracy of the Parameter extraction. In contrast to most of the published experiments, we are able to reliably investigate samples with thicknesses as small as 100μm, samples with low indexes of refraction, i.e. close to 1, as well as samples with sharp peaks in the Material Parameter curves.
Pablo Lamata - One of the best experts on this subject based on the ideXlab platform.
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myocardial transversely isotropic Material Parameter estimation from in silico measurements based on a reduced order unscented kalman filter
Journal of The Mechanical Behavior of Biomedical Materials, 2011Co-Authors: Pablo Lamata, Jack Lee, Philippe Moireau, Dominique Chapelle, Nic SmithAbstract:Abstract Parameter estimation from non-invasive measurements is a crucial step in patient-specific cardiac modeling. It also has the potential to provide significant assistance in the clinical diagnosis of cardiac diseases through the quantification of myocardial Material heterogeneity. In this paper, we formulate a novel Reduced-order Unscented Kalman Filter (rUKF) applied to the left ventricular (LV) nonlinear mechanical model based on cubic-Hermite finite elements. Material Parameters in the widely-employed transversely isotropic Guccione’s constitutive law are successfully identified for both homogeneous and heterogeneous cases. We conclude that the four Parameters in Guccione’s law can be uniquely and correctly determined in-silico from noisy displacement measurements of Material points located on the myocardial surfaces. The future application of this novel and effective approach to real clinical measurements is thus promising.