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Author: Juvenal Ormachea Quispe Publisher: ISBN: Category : Languages : en Pages : 195
Book Description
"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: Juvenal Ormachea Quispe Publisher: ISBN: Category : Languages : en Pages : 195
Book Description
"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: Sudhakar K. Venkatesh Publisher: Springer ISBN: 1493915754 Category : Medical Languages : en Pages : 143
Book Description
The first book to cover the groundbreaking development and clinical applications of Magnetic Resonance Elastography, this book is essential for all practitioners interested in this revolutionary diagnostic modality. The book is divided into three sections. The first covers the history of MRE. The second covers technique and clinical applications of MRE in the liver with respect to fibrosis, liver masses, and other diseases. Case descriptions are presented to give the reader a hands-on approach. The final section presents the techniques, sequence and preliminary results of applications in other areas of the body including muscle, brain, lung, heart, and breast.
Author: José Fernando Zvietcovich Zegarra Publisher: ISBN: Category : Languages : en Pages : 221
Book Description
"Dynamic optical coherence elastography (OCE) is a functional imaging modality which leverages the propagation of mechanical waves in order to estimate the mechanical properties of tissues. It is very useful since it does not require (i) a priori knowledge of force/stress, (ii) mandatory direct contact between the mechanical loading source and the tissue under study, and (iii) large deformation of tissues. Therefore, dynamic OCE shows promise for non-contact, in situ, and in vivo mechanical characterization of tissues with applications in laboratory and clinical studies. To date, the impact of using transient/continuous temporal excitation produced by one/multiple loading sources on the effectiveness of OCE methods for the elastic characterization of tissues has not been fully explored. Further, due to the small field of view of optical coherence tomography (OCT) (~ 2 mm along depth), the complexity of boundary conditions of tissues (such as heterogeneous, composite, or plate-shaped media), and the excitation wavelength (typically between 0.1 mm 10 mm), surface acoustic waves (SAW) are the dominant perturbation. These diminish the capability of OCE methods to estimate depth-dependent tissue elasticity information (such as in layered or composite materials). Moreover, the estimation of viscous parameters in addition to the classic elastic modulus is of great interest since it can provide useful information of disease stages. However, most OCE methods assume a rheological model of tissues and utilize only frequency-dependent wave speed measurements, disregarding valuable information given by the wave attenuation process. Finally, the exploration of novel dynamic OCE techniques to address the aforementioned issues, including the aberration of waves in heterogeneous and anisotropic media and the multiple wave reflections produced by irregular boundary conditions, is highly desired. In this thesis, a comparative study of transient and continuous dynamic OCE methods and estimators when using one or two vibration sources is conducted. Resolution, accuracy error, precision error, and contrast-to-noise ratio are the selected metrics for evaluating the performance of each method in numerical simulations and experiments in tissue-mimicking phantoms. Furthermore, a novel OCE method based on reverberant shear wave fields in elastic media is presented. This method arose as a response to the limitations found in the comparative study developed previously. Numerical simulations and experiments in ex vivo porcine cornea demonstrate the capabilities of the proposed technique for layered material elastic characterization compared to SAW-based OCE methods. Subsequently, a novel technique for the viscoelastic characterization of tissues by propagating Gaussian-shape transient waves using acoustic radiation force (ARF) excitation is developed. Experimental results in viscoelastic tissue-mimicking phantoms validated the proposed approach, accounting for dispersion, distortion, and attenuation of transient waves while not assuming any rheological model for tissue characterization. In addition, a study on longitudinal shear waves generated using a disk-shaped glass plate for the elastic characterization of heterogeneous distributed media is presented. Numerical simulations and experiments in tissue-mimicking phantoms demonstrate the capabilities and difficulties of such waves in detecting vertically and horizontally distributed materials. Preliminary experiments in mouse brain tissue are conducted followed by a discussion on future implementations of this method for in vivo mouse brain elastography studies. Finally, the elastography of small substructures in rabbit cornea produced by localized laser-induced refractive index change (LIRIC treatment) using OCE techniques is explored. In addition, the study of anisotropic tissues (chicken tibialis muscle and porcine brain) using non-contact ARF excitation is conducted. In these studies, a transverse isotropic mechanical model is used and validated. In summary, we have (i) conducted a series of studies using numerical simulations and tissue-mimicking phantoms to understand the nature, properties, and capabilities of mechanical waves for the elastography of tissues; (ii) developed a set of novel dynamic OCE approaches that are capable of detecting subtle changes (>13% change in elastic properties) within tissues, and with a spatial resolution as low as 120 um along lateral axis and 55.5 um along depth axis; and (iii) applied these approaches to the study of tissues with different boundary conditions (composite plate-shaped media such as cornea, mouse in situ brain tissue, etc.) and diverse mechanical properties (viscoelastic, heterogeneous, and anisotropic tissues)"--Pages xviii-xxi.
Author: Ivan Z. Nenadic Publisher: John Wiley & Sons ISBN: 1119021545 Category : Technology & Engineering Languages : en Pages : 919
Book Description
Ultrasound Elastography for Biomedical Applications and Medicine Ivan Z. Nenadic, Matthew W. Urban, James F. Greenleaf, Mayo Clinic Ultrasound Research Laboratory, Mayo Clinic College of Medicine, USA Jean-Luc Gennisson, Miguel Bernal, Mickael Tanter, Institut Langevin – Ondes et Images, ESPCI ParisTech CNRS, France Covers all major developments and techniques of Ultrasound Elastography and biomedical applications The field of ultrasound elastography has developed various techniques with the potential to diagnose and track the progression of diseases such as breast and thyroid cancer, liver and kidney fibrosis, congestive heart failure, and atherosclerosis. Having emerged in the last decade, ultrasound elastography is a medical imaging modality that can noninvasively measure and map the elastic and viscous properties of soft tissues. Ultrasound Elastography for Biomedical Applications and Medicine covers the basic physics of ultrasound wave propagation and the interaction of ultrasound with various media. The book introduces tissue elastography, covers the history of the field, details the various methods that have been developed by research groups across the world, and describes its novel applications, particularly in shear wave elastography. Key features: Covers all major developments and techniques of ultrasound elastography and biomedical applications. Contributions from the pioneers of the field secure the most complete coverage of ultrasound elastography available. The book is essential reading for researchers and engineers working in ultrasound and elastography, as well as biomedical engineering students and those working in the field of biomechanics.
Author: Ivan Z. Nenadic Publisher: John Wiley & Sons ISBN: 1119021510 Category : Technology & Engineering Languages : en Pages : 613
Book Description
Ultrasound Elastography for Biomedical Applications and Medicine Ivan Z. Nenadic, Matthew W. Urban, James F. Greenleaf, Mayo Clinic Ultrasound Research Laboratory, Mayo Clinic College of Medicine, USA Jean-Luc Gennisson, Miguel Bernal, Mickael Tanter, Institut Langevin – Ondes et Images, ESPCI ParisTech CNRS, France Covers all major developments and techniques of Ultrasound Elastography and biomedical applications The field of ultrasound elastography has developed various techniques with the potential to diagnose and track the progression of diseases such as breast and thyroid cancer, liver and kidney fibrosis, congestive heart failure, and atherosclerosis. Having emerged in the last decade, ultrasound elastography is a medical imaging modality that can noninvasively measure and map the elastic and viscous properties of soft tissues. Ultrasound Elastography for Biomedical Applications and Medicine covers the basic physics of ultrasound wave propagation and the interaction of ultrasound with various media. The book introduces tissue elastography, covers the history of the field, details the various methods that have been developed by research groups across the world, and describes its novel applications, particularly in shear wave elastography. Key features: Covers all major developments and techniques of ultrasound elastography and biomedical applications. Contributions from the pioneers of the field secure the most complete coverage of ultrasound elastography available. The book is essential reading for researchers and engineers working in ultrasound and elastography, as well as biomedical engineering students and those working in the field of biomechanics.
Author: Armin Schneider Publisher: Academic Press ISBN: 0128032316 Category : Technology & Engineering Languages : en Pages : 592
Book Description
Biomedical Engineering in Gastrointestinal Surgery is a combination of engineering and surgical experience on the role of engineering in gastrointestinal surgery. There is currently no other book that combines engineering and clinical issues in this field, while engineering is becoming more and more important in surgery. This book is written to a high technical level, but also contains clear explanations of clinical conditions and clinical needs for engineers and students. Chapters covering anatomy and physiology are comprehensive and easy to understand for non-surgeons, while technologies are put into the context of surgical disease and anatomy for engineers. The authors are the two most senior members of the Institute for Minimally Invasive Interdisciplinary Therapeutic Interventions (MITI), which is pioneering this kind of collaboration between engineers and clinicians in minimally invasive surgery. MITI is an interdisciplinary platform for collaborative work of surgeons, gastroenterologists, biomedical engineers and industrial companies with mechanical and electronic workshops, dry laboratories and comprehensive facilities for animal studies as well as a fully integrated clinical "OR of the future". Written by the head of the Institute of Minimally Invasive Interdisciplinary Therapeutic Intervention (TUM MITI) which focusses on interdisciplinary cooperation in visceral medicine Provides medical and anatomical knowledge for engineers and puts technology in the context of surgical disease and anatomy Helps clinicians understand the technology, and use it safely and efficiently
Author: Pouria Hajikarimi Publisher: Elsevier ISBN: 012821211X Category : Technology & Engineering Languages : en Pages : 245
Book Description
Applications of Viscoelasticity: Bituminous Materials Characterization and Modeling starts with an introduction to the theory of viscoelasticity, emphasizing its importance to various applications in material characterization and modeling. It next looks at constitutive viscoelastic functions, outlines basic equations for different loading conditions, and introduces the Boltzmann superposition principle, relaxation modulus, and creep compliance. Mechanical models, including integer-order and fractional-order are studied next, featuring real experimentation data alongside the benefits and drawbacks of using each model in various real-world scenarios. The book then covers the correspondence principle, followed by time–temperature superposition, featuring a simple procedure to construct a real master curve and challenges that might be encountered. The concluding chapters cover the Hopkins and Hamming, Park and Kim, and General Power law methods for interconversion of constitutive viscoelastic functions, applications of viscoelasticity for experimental tests, and incremental form of viscoelastic relations for numerical modeling. The book also includes supplementary codes that users can duplicate and use in their own work. Takes an applied approach to material viscoelasticity, explaining complicated viscoelastic equations and principles Presents examples of those equations and principles being applied to common problems in realworld settings Covers constitutive viscoelastic functions, including relaxation modulus and creep compliance Outlines the construction of a master curve of viscoelastic material considering time–temperature superposition Couples the correspondence principle with common viscoelastic experiments, such as threepoint bending beam, axial and torsional bar, and dynamic shear rheometer Provides supplementary codes
Author: Juvenal Ormachea Quispe
Author: Juvenal Ormachea Quispe
Author: Sudhakar K. Venkatesh
Author: Ivana Dusan Pajic-Lijakovic
Author: José Fernando Zvietcovich Zegarra
Author: Ivan Z. Nenadic
Author: Ivan Z. Nenadic
Author: Armin Schneider
Author: Corin F. Oteşteanu
Author: Simon Chatelin
Author: Pouria Hajikarimi