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Visualization of atherosclerotic plaque mechanical properties using model based intravascular ultrasound elastography.
Abstract
Cardiovascular disease related deaths occur primarily from fatty plaques inside an artery that rupture and cause clots that disrupt blood flow. The study of arterial plaque mechanics is essential to the monitoring of atherosclerosis and the detection of vulnerable plaques or the likelihood of their rupture. The aim of this work is to measure and image the mechanical behavior of plaques using a clinically available intravascular ultrasound system (IVUS). To test the methods, radial displacements were measured from simulated images and phantom data within two dimensional IVUS rf images using standard elastography techniques. Simulations and phantom experiments were designed to mimic arterial geometries and deformations, which include plaque regions of varying stiffnesses. In addition, an optimization inversion algorithm was used to infer the elastic modulus of the underlying material. This algorithm utilizes a finite element based model and assumes that the deformation is quasi-static, plane strain and that the material is incompressible and linear elastic. The full spatially reconstructed modulus images, with no geometric constraints, are presented and compared to radial strain images. The phantom results are compared to the known modulus contrasts, and the simulated images are compared to contrasts and distributions.
... Use of the transcutaneous method for therapy monitoring has also been reported with promising results [318]. Further investigations are continuing [319] and this area has promise but faces significant technical hurdles before widespread clinical use becomes practical. ...
From times immemorial manual palpation served as a source of information on the state of soft tissues and allowed detection of various diseases accompanied by changes in tissue elasticity. During the last two decades, the ancient art of palpation gained new life due to numerous emerging elasticity imaging (EI) methods. Areas of applications of EI in medical diagnostics and treatment monitoring are steadily expanding. Elasticity imaging methods are emerging as commercial applications, a true testament to the progress and importance of the field. In this paper we present a brief history and theoretical basis of EI, describe various techniques of EI, analyze their advantages and limitations, and overview main clinical applications. We present a classification of elasticity measurement and imaging techniques based on the methods used for generating a stress in the tissue (external mechanical force, internal ul-trasound radiation force, or an internal endogenous force), and measurement of the tissue response. The measurement method can be performed using differing physical principles including magnetic resonance imaging (MRI), ultrasound imaging, X-ray imaging, optical and acoustic signals. Until recently, EI was largely a research method used by a few select institutions having the special equipment needed to perform the studies. Since 2005 however, increasing numbers of mainstream manufacturers have added EI to their ultra-sound systems so that today the majority of manufacturers offer some sort of Elastography or tissue stiffness imaging on their clinical systems. Now it is safe to say that some sort of elasticity imaging may be performed on virtually all types of focal and diffuse disease. Most of the new applications are still in the early stages of research, but a few are becoming common applications in clinical practice.
... Use of the transcutaneous method for therapy monitoring has also been reported with promising results [318]. Further investigations are continuing [319] and this area has promise but faces significant technical hurdles before widespread clinical use becomes practical. ...
From times immemorial manual palpation served as a source of information on the state of soft tissues and allowed detection of various diseases accompanied by changes in tissue elasticity. During the last two decades, the ancient art of palpation gained new life due to numerous emerging elasticity imaging (EI) methods. Areas of applications of EI in medical diagnostics and treatment monitoring are steadily expanding. Elasticity imaging methods are emerging as commercial applications, a true testament to the progress and importance of the field. In this paper we present a brief history and theoretical basis of EI, describe various techniques of EI, analyze their advantages and limitations, and overview main clinical applications. We present a classification of elasticity measurement and imaging techniques based on the methods used for generating a stress in the tissue (external mechanical force, internal ul-trasound radiation force, or an internal endogenous force), and measurement of the tissue response. The measurement method can be performed using differing physical principles including magnetic resonance imaging (MRI), ultrasound imaging, X-ray imaging, optical and acoustic signals. Until recently, EI was largely a research method used by a few select institutions having the special equipment needed to perform the studies. Since 2005 however, increasing numbers of mainstream manufacturers have added EI to their ultra-sound systems so that today the majority of manufacturers offer some sort of Elastography or tissue stiffness imaging on their clinical systems. Now it is safe to say that some sort of elasticity imaging may be performed on virtually all types of focal and diffuse disease. Most of the new applications are still in the early stages of research, but a few are becoming common applications in clinical practice.
... Use of the transcutaneous method for therapy monitoring has also been reported with promising results [318]. Further investigations are continuing [319] and this area has promise but faces sig- nificant technical hurdles before widespread clinical use be- comes practical. ...
Radiation force is a universal phenomenon in any wave motion, electromagnetic or acoustic. Radiation force is produced by a change in the density of energy of the propagating wave. The concept of radiation pressure follows from Maxwell?s equations (1871), while the idea of electromagnetic wave (light) pressure can be traced back to Johannes Kepler (1619). Acoustic radiation force was first experimentally demonstrated by August Kundt (1874) and its physical bases were analyzed in classical works of Lord Rayleigh (1902), L. Brillouin, and P. Langevin. Until recently, main biomedical application of acoustic radiation force was in measuring acoustic power of therapeutic devices, but during the last 15 years it became one of the hottest areas of biomedical ultrasonics with numerous new applications ranging from acoustical tweezers, targeted drug and gene delivery, manipulating of cells in suspension, increasing the sensitivity of biosensors and immunochemical tests, assessing viscoelastic properties of fluids and biological tissue, and monitoring lesions during therapy. The widest new area of applications of radiation force is related to medical imaging in general and elasticity imaging specifically. Remote excitation of shear stress in a given site in the body using radiation force of focused ultrasound offers numerous new possibilities for medical diagnostics.
... Use of the transcutaneous method for therapy monitoring has also been reported with promising results [318]. Further investigations are continuing [319] and this area has promise but faces significant technical hurdles before widespread clinical use becomes practical. ...
From times immemorial manual palpation served as a source of information on the state of soft tissues and allowed detection of various diseases accompanied by changes in tissue elasticity. During the last two decades, the ancient art of palpation gained new life due to numerous emerging elasticity imaging (EI) methods. Areas of applications of EI in medical diagnostics and treatment monitoring are steadily expanding. Elasticity imaging methods are emerging as commercial applications, a true testament to the progress and importance of the field.In this paper we present a brief history and theoretical basis of EI, describe various techniques of EI and, analyze their advantages and limitations, and overview main clinical applications. We present a classification of elasticity measurement and imaging techniques based on the methods used for generating a stress in the tissue (external mechanical force, internal ultrasound radiation force, or an internal endogenous force), and measurement of the tissue response. The measurement method can be performed using differing physical principles including magnetic resonance imaging (MRI), ultrasound imaging, X-ray imaging, optical and acoustic signals.Until recently, EI was largely a research method used by a few select institutions having the special equipment needed to perform the studies. Since 2005 however, increasing numbers of mainstream manufacturers have added EI to their ultrasound systems so that today the majority of manufacturers offer some sort of Elastography or tissue stiffness imaging on their clinical systems. Now it is safe to say that some sort of elasticity imaging may be performed on virtually all types of focal and diffuse disease. Most of the new applications are still in the early stages of research, but a few are becoming common applications in clinical practice.
... Although feasible for quasi-static breast elastography, this method would be difficult to implement in other approaches to elastography. An alternate approach is to incorporate structural information in the image reconstruction process (Richards et al., 2010; Baldewsing et al., 2006; Baldewsing et al., 2005b; Le Floc'h et al., 2009; Le Floc'h et al., 2010). Structural information can be obtained by segmenting images obtained from ultrasound, MR, or other sources. ...
Elastography is emerging as an imaging modality that can distinguish normal versus diseased tissues via their biomechanical properties. This paper reviews current approaches to elastography in three areas--quasi-static, harmonic and transient--and describes inversion schemes for each elastographic imaging approach. Approaches include first-order approximation methods; direct and iterative inversion schemes for linear elastic; isotropic materials and advanced reconstruction methods for recovering parameters that characterize complex mechanical behavior. The paper's objective is to document efforts to develop elastography within the framework of solving an inverse problem, so that elastography may provide reliable estimates of shear modulus and other mechanical parameters. We discuss issues that must be addressed if model-based elastography is to become the prevailing approach to quasi-static, harmonic and transient elastography: (1) developing practical techniques to transform the ill-posed problem with a well-posed one; (2) devising better forward models to capture the complex mechanical behavior of soft tissues and (3) developing better test procedures to evaluate the performance of modulus elastograms.
Elastography or elasticity imaging is a field of medical imaging that is aimed at quantifying the mechanical properties of living tissues. Fibrosis results from an increase in collagen replacing the normal tissue, which makes the organ stiffer than when the healthy functional units are present. Palpation has several disadvantages, including its subjectivity, dependence on the proficiency of the examiner, reproducibility, and insensitivity to deep structures. Elastography offers an approach for noninvasive, reproducible, objective, and high resolution characterization of the mechanical properties of tissues. This chapter focuses on ultrasound‐based methods. It highlights the magnetic resonance elastography results in certain application areas. Liver fibrosis and steatosis have been the target diseases for many shear wave elastography studies. Breast and thyroid cancer diagnosis and differentiation have been the application areas for strain‐based and, more recently, shear wave elastography methods. Ultrasound of the musculoskeletal system has been growing progressively.
Carotid endarterectomy (CEA) is currently accepted as the gold standard for interventional revascularisation of diseased arteries belonging to the carotid bifurcation. Despite the proven efficacy of CEA, great interest has been generated in carotid angioplasty and stenting (CAS) as an alternative to open surgical therapy. CAS is less invasive compared with CEA, and has the potential to successfully treat lesions close to the aortic arch or distal internal carotid artery (ICA). Following promising results from two recent trials (CREST; Carotid revascularisation endarterectomy versus stenting trial, and ICSS; International carotid stenting study) it is envisaged that there will be a greater uptake in carotid stenting, especially amongst the group who do not qualify for open surgical repair, thus creating pressure to develop computational models that describe a multitude of plaque models in the carotid arteries and their reaction to the deployment of such interventional devices. Pertinent analyses will require fresh human atherosclerotic plaque material characteristics for different disease types. This study analysed atherosclerotic plaque characteristics from 18 patients tested on site, post-surgical revascularisation through endarterectomy, with 4 tissue samples being excluded from tensile testing based on large width-length ratios. According to their mechanical behaviour, atherosclerotic plaques were separated into 3 grades of stiffness. Individual and group material coefficients were then generated analytically using the Yeoh strain energy function. The ultimate tensile strength (UTS) of each sample was also recorded, showing large variation across the 14 atherosclerotic samples tested. Experimental Green strains at rupture varied from 0.299 to 0.588 and the Cauchy stress observed in the experiments was between 0.131 and 0.779 MPa. It is expected that this data may be used in future design optimisation of next generation interventional medical devices for the treatment and revascularisation of diseased arteries of the carotid bifurcation.
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