Elucidation of Isotropic and Anisotropic Shear Elasticity of in Vivo Soft Tissue Using Planar Magnetic Resonance Elastography PDF Download

Author: Sebastian Papazoglou
Publisher:
ISBN:
Category :
Languages : en
Pages : 99

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Author: Yan-Ping Huang
Publisher: CRC Press
ISBN: 1466576294
Category : Medical
Languages : en
Pages : 226

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The product of 20 years of research, this book covers topics in soft tissue elasticity in vivo, from measurement techniques to clinical applications. It provides, for the first time, a single source that systematically introduces the various techniques for in vivo measurement of soft tissue elasticity in an effort to ease the difficulty between lea

Author: Daniel R. Smith
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Human soft tissues are highly complex networks comprised of a variety of components that contribute to the overall functionality of the tissue, but these structures can be disrupted through injury or pathology, leading to tissue dysfunction. Magnetic resonance elastography (MRE) is a developing imaging technique that has shown promise in evaluating human soft tissues in-vivo by providing mechanical property estimates that are sensitive to structural changes in these tissues, including sensitivity to pathological changes. While MRE has proved to be an effective technique in much of human soft tissue, fibrous soft tissues, such as brain white matter and skeletal muscle, cause standard assumptions of mechanical isotropy to fail, resulting in data-model mismatches and inaccurate evaluations of tissue integrity and health. In this thesis, we propose to develop and test an MRE method to evaluate the health of fibrous soft tissues by evaluating structural and functional changes from pathology or injury.

Author: Ivana Dusan Pajic-Lijakovic
Publisher: Frontiers Media SA
ISBN: 2889716953
Category : Science
Languages : en
Pages : 161

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Author: Stéphane Avril
Publisher: Springer
ISBN: 3319450719
Category : Technology & Engineering
Languages : en
Pages : 161

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The articles in this book review hybrid experimental-computational methods applied to soft tissues which have been developed by worldwide specialists in the field. People developing computational models of soft tissues and organs will find solutions for calibrating the material parameters of their models; people performing tests on soft tissues will learn what to extract from the data and how to use these data for their models and people worried about the complexity of the biomechanical behavior of soft tissues will find relevant approaches to address this complexity.

Author: Ali Zorgani
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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The aim of this thesis was the development of a new approach called passive elastography. This approach is inspired from noise correlation methods well developed in seismology and time reversal technics in acoustics. Passive elastography uses shear waves naturally induced in the human body to extract its mechanical properties of soft tissue. The feasibility of this method was tested in several applications. First in ultrasound, slow frame rate ultrasound scanner was used to monitor high intensity focused ultrasound treatment on porcine pancreas. Then, an ultrafast ultrasound scanner was used to retrieve shear wave speed map in a calibrated phantom and in-vivo. Second, Magnetic resonance elastography was implemented to image natural motion in the brain of healthy volunteers and conduct shear wavelength tomography. Third, of ophthalmological and dermatological applications, optical coherence passive elastography was tested in a phantom and a cornea of healthy mouse. Also, a fully optical setup was established to image surface wave for elastography applications. Finally, the resolution limit of elastography was measured using and ultrasound ultrafast scanner.

Author: Juvenal Ormachea Quispe
Publisher:
ISBN:
Category :
Languages : en
Pages : 195

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"Elastography is a rapidly growing field in which imaging systems are used to estimate the viscoelastic properties of tissue. For example, elevated liver stiffness is an important indicator of fibrosis, and so the diagnostic value of elastography adds new information to the conventional radiology image. Within elastography techniques, shear waves play an important role, as they can be propagated by a source through the soft tissues and tracked by the imaging system. The distinction between shear wave group and phase velocities is important in elastography, because diagnoses are made using a variety of techniques on different scanners: some rely on group velocity estimates, but others assess phase velocity. This document reviews the general definitions of group and phase velocity and examines their specific relations within an important general class of rheological models. For the class of tissues and materials exhibiting power law dispersion, group velocity is significantly greater than phase velocity, and simple expressions are shown to interrelate the commonly measured parameters. Examples are given from phantoms and tissues. This thesis then considers the propagation of shear waves from acoustic radiation impulsive forces. Parameter estimation of the shear wave speed in tissues are based on some underlying models of shear wave propagation. The models typically include specific choices of the spatial and temporal shape of the force impulse and the elastic or viscoelastic properties of the medium. In this work, the analytical treatment of 2-D shear wave propagation in a biomaterial is presented. Estimators of attenuation and shear wave speed are derived from the analytical solutions, and these are applied to an elastic phantom, a viscoelastic phantom, and in vivo liver using a clinical ultrasound scanner. Additionally, it shows and examines the rheological models that can capture the dominant viscoelastic behaviors associated with fat and inflammation in the liver, and quantifies the resulting changes in shear wave speed and viscoelastic parameters. Theoretical results are shown to match measurements in phantoms and animal studies reported in the literature. Finally, the shear wave attenuation parameter, and its relation to diseased states of the liver, is studied. This work focused on the hypothesis that steatosis adds a viscous (lossy) component to the liver, which increases shear wave attenuation. Twenty patients' livers were scanned and the resulting displacement profiles were analyzed to derive both the speed and attenuation of the shear waves within 6-cm2 regions of interest. The results were compared with pathology scores obtained from ultrasound-guided liver biopsies taken under ultrasound guidance. Across these cases, increases in shear wave attenuation were linked to increased steatosis score. This preliminary study supports the hypothesis and indicates the possible utility of the measurements for non-invasive and quantitative assessment of steatosis. The shear wave speed estimators can be relatively simple if plane wave behavior is assumed with a known direction of propagation as it is considered in several elastography methods based on acoustic radiation force impulse. However, multiple reflections from organ boundaries and internal inhomogeneities and mode conversions can create a complicated field in time and space. Thus, this work also explores the mathematics of multiple component shear wave fields and derives the basic properties. It approaches this problem from the historic perspective of reverberant fields, a conceptual framework used in architectural acoustics and related fields. The reverberant shear wave field approach was evaluated and compared with another well-known elastography technique using two calibrated elastic and viscoelastic phantoms. The results indicate that it is possible to estimate the viscoelastic properties in each scanned medium. Moreover, the simultaneous multi-frequency application can be accomplished by applying an array of external sources that can be excited by multiple frequencies within a bandwidth, all contributing to the shear wave field produced in the liver or other target organ. This enables the analysis of the dispersion of shear wave speed as it increases with frequency, indicating the viscoelastic and lossy nature of the tissue under study. Furthermore, complete 2-D dispersion images can be created and displayed alongside the shear wave speed images. The author reports preliminary studies on in vivo breast and liver tissues, employing frequencies up to 700 Hz in breast tissue, and robust reverberant patterns of shear waves across the entire liver and kidney in obese patients. Dispersion images are shown to have contrast between tissue types and with quantitative values that align with previous studies. In addition to the shear wave speed and dispersion, this thesis also reports, numerically and experimentally, that it is possible to assess shear wave attenuation in tissues by using a reverberant shear wave field. The shear wave attenuation coefficient results are in agreement with those obtained in previous studies reported in the literature. In that sense, the R-SWE approach shows the potential to obtain a complete rheological characterization in in vivo tissue by measuring the shear wave speed, shear wave dispersion, and shear wave attenuation. Finally, the specific conclusions of this research are summarized in the last chapter, with a special emphasis of next steps and future work that can be accomplished to improve the results presented in this work"--Pages xv-xvii.

Author: Julian J. Wu
Publisher: SIAM
ISBN: 9780898712896
Category : Science
Languages : en
Pages : 394

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A selection of 26 original papers, some of them substantially revised after the workshop, discuss anisotropic elasticity and its applications in solid mechanics and applied mathematics. Considering elastostatics, elastodynamics, and constitutive relations, they discuss such topics as Green's functio

Author: Christoph Moosbauer
Publisher: Anchor Academic Publishing (aap_verlag)
ISBN: 395489906X
Category : Technology & Engineering
Languages : en
Pages : 118

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Book Description
Since the early 1990’s, elasticity imaging techniques are developed as a powerful supplement of the medical toolbox in diagnostic analysis and computer aided surgery. By solving a so-called inverse problem, information about the spatial variation of material parameters of soft (human) tissue are derived from displacement data, which can be measured noninvasively using standard imaging devices such as ultrasound or magnetic resonance tomography. The terms of quasi-static and dynamic elastography refer to the type of load situation, by which the tissue in question is excited. The extension of the theoretical formulation and implementation of the underlying inverse problem in quasi-static elastography to time-harmonic approaches poses several additional challenges, which are addressed in detail within the course of this study. We propose a robust strategy for the reconstruction, which takes advantage of the high sensitivity of the accuracy in harmonic elastography to the choice of the starting point. While not being reported in the literature up to now, the quite competing claims of quasi-static and time-harmonic elastography motivate a comprehensive comparison of these two techniques. Via a spectral decomposition of the curvature information of the underlying inverse problem, a clear explanation for an improved robustness of time- harmonic elastography in the presence of inaccuracies due to noise and/or numerical approximations can be given. Several numerical examples confirm these findings as well as the efficiency of the proposed reconstruction strategy. In particular, it is shown that for moderately low frequencies, it is sufficient to use very coarse finite element meshes, so that the only additional computational cost stems from the worse conditioning of the system matrix.

Author: Soumya Goswami
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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"Imaging of tissue mechanical properties has shown promise in non-invasive evaluation of diverse pathologies. While there has been considerable research on imaging linear tissue mechanical properties in laboratory and clinical settings, little research has been done to image the nonlinear tissue mechanical properties. Recently, research on multiple complex nonlinear mechanical effects such as frequency-dependence, anisotropy and nonlinear elasticity are gaining prominence. However, imaging of these nonlinear mechanical properties are challenging particularly for deep organs. In this study, we first propose a tissue nonlinear elasticity imaging method combining strain and shear wave elastography. This method produces high contrast non-linear elastograms under conditions of pure uni-axial compression, but exhibit bias errors of 10-50 % when the applied deformation deviates from the uni-axial condition. Since freehand transducer motion generally does not produce pure uniaxial compression, a motion-agnostic non-linearity estimator is desirable for clinical translation. Here we derive an expression for measurement of the Non-Linear Shear Modulus (NLSM) of tissue subject to combined shear and axial deformations. Further, we developed a nonlinear elastography model that combines strain measurements from arbitrary tissue deformation with radiation-force based broadband shear wave speed measurements. Again, shear wave measurements are highly influenced by other tissue mechanical properties like tissue viscosity. Hence, a concurrent assessment of these complex effects may enable a more complete characterization of tissue biomechanics and offer improved diagnostic sensitivity. In this work we report for the first time a method to map the frequency-dependent nonlinear parameters of soft tissues on a local scale. Here, we extended this model to incorporate local measurements of frequency-dependent shear modulus. This combined approach provides a local frequency dependent nonlinear parameter that can be obtained with arbitrary, clinically realizable tissue compression. Initial assessments using simulations and phantoms validate the accuracy of this approach. We also observed improved contrast in nonlinearity parameter at higher frequencies. Results from ex-vivo liver experiments show 32 dB, 25 dB, dB, 34 dB, and 38 dB higher contrast in elastograms than traditional linear elasticity, elastic nonlinearity, viscosity and strain imaging methods, respectively. A lesion, artificially created by injection of glutaraldehyde into a liver specimen, showed a 59% increase in the frequency dependent nonlinear parameter and 17% increase in contrast ratio"--Pages xv-xvi