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Journal ArticleDOI

Measurement of Viscoelastic Properties of Polyacrylamide-Based Tissue-Mimicking Phantoms for Ultrasound Elastography Applications

05 Apr 2010-IEEE Transactions on Instrumentation and Measurement (IEEE)-Vol. 59, Iss: 5, pp 1224-1232
TL;DR: Polyacrylamide gel based tissue-mimicking phantoms have been developed to experimentally study the role of viscoelastic properties inPhantoms and indicate that stiffer samples exhibit large variations in the storage modulus when the precompression levels are altered.

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Abstract: Many ailments and/or malfunctions of the body have been observed to change the viscous behavior and elastic properties of biological soft tissues. The technique of elastography has evolved to image such properties. The clinical evidence gathered during studies involving elastography to identify cancerous lesions is very promising. However, the quantification of the resolution and specificity of elastography is best achieved under a controlled study using tissue-mimicking phantoms. One challenge is to reproduce viscoelastic behavior in phantoms as observed in biological tissues. In this paper, polyacrylamide gel based tissue-mimicking phantoms have been developed to experimentally study the role of viscoelastic properties in a controlled manner. To measure the Young's modulus, the phantoms were subjected to linear loading, and the stress-strain relationship is deduced therefrom. It is seen that the phantoms show hysteresis behavior. The viscoelastic properties of these phantoms were measured by subjecting the samples to cyclic loading. Normal forces during this process of loading were also measured as a measure of sample elasticity. To emulate the normal and pathological lesions, samples were prepared with varying concentration of monomer and studied. Three models, namely, Maxwell, Kelvin-Voigt (KV), and Kelvin-Voigt fractional derivative (KVFD), were chosen to fit the experimental data. Of these, the KVFD model was found to be best fitting for the experimental data obtained. Results indicate that stiffer samples exhibit large variations in the storage modulus when the precompression levels are altered.

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Topics: Elastography (53%), Dynamic modulus (52%), Viscoelasticity (50%)
Citations
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Journal ArticleDOI
TL;DR: OCE techniques, including the development of intravascular- or catheter-based OCE, are in their early stages of development but show great promise for surgical oncology or intrav vascular cardiology applications.

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Abstract: Optical coherence tomography (OCT) has several advantages over other imaging modalities, such as angiography and ultrasound, due to its inherently high in vivo resolution, which allows for the identification of morphological tissue structures. Optical coherence elastography (OCE) benefits from the superior spatial resolution of OCT and has promising applications, including cancer diagnosis and the detailed characterization of arterial wall biomechanics, both of which are based on the elastic properties of the tissue under investigation. We present OCE principles based on techniques associated with static and dynamic tissue excitation, and their corresponding elastogram image-reconstruction algorithms are reviewed. OCE techniques, including the development of intravascular- or catheter-based OCE, are in their early stages of development but show great promise for surgical oncology or intravascular cardiology applications.

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172 citations


Journal ArticleDOI
Abstract: In this study, for the first time, the transverse vibrational model of a viscous-fluid-conveying single-walled carbon nanotube (SWCNT) embedded in biological soft tissue is developed. Nonlocal Euler–Bernoulli beam theory has been used to investigate fluid-induced vibration of the SWCNT while visco-elastic behaviour of the surrounding tissue is simulated by the Kelvin–Voigt model. The results indicate that the resonant frequencies and the critical flow velocity at which structural instability of nanotubes emerges are significantly dependent on the properties of the medium around the nanotube, the boundary conditions, the viscosity of the fluid and the nonlocal parameter. Detailed results are demonstrated for the dependence of damping and elastic properties of the medium on the resonant frequencies and the critical flow velocity. Three standard boundary conditions, namely clamped–clamped, clamped–pinned and pinned–pinned, are applied to study the effect of the supported end conditions. Furthermore, it is found that the visco-elastic foundation causes an obvious reduction in the critical velocity in comparison with the elastic foundation, in particular for a compliant medium, pinned–pinned boundary condition, high viscosity of the fluid and small values of the nonlocal coefficient.

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79 citations


Journal ArticleDOI
Abstract: Nonlinear free vibration and instability of fluid-conveying double-walled boron nitride nanotubes (DWBNNTs) embedded in viscoelastic medium are studied in this paper. The effects of the transverse shear deformation and rotary inertia are considered by utilizing the Timoshenko beam theory. The size effect is applied by the modified couple stress theory and considering a material length scale parameter for beam model. The nonlinear effect is considered by the Von Karman type geometric nonlinearity. The electromechanical coupling and charge equation are employed to consider the piezoelectric effect. The surrounding viscoelastic medium is described as the linear visco-Pasternak foundation model characterized by the spring and damper. Hamilton’s principle is used to derive the governing equations and boundary conditions. The differential quadrature method (DQM) is employed to discretize the nonlinear higher-order governing equations, which are then solved by a direct iterative method to obtain the nonlinear vibration frequency and critical fluid velocity of fluid-conveying DWBNNTs with clamped-clamped (C-C) boundary conditions. A detailed parametric study is conducted to elucidate the influences of the small scale coefficient, spring and damping constants of surrounding viscoelastic medium and fluid velocity on the nonlinear free vibration, instability and electric potential distribution of DWBNNTs. This study might be useful for the design and smart control of nano devices.

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35 citations


Journal ArticleDOI
TL;DR: The frequency-shift method, used in ultrasound imaging and seismology, was adapted for shear-wave attenuation measurement in elastography, and provides tissue attenuation, which is relevant diagnostic information to model viscosity, in addition to sheer-wave velocity used to assess elasticity.

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Abstract: In vivo quantification of shear-wave attenuation in soft tissues may help to better understand human tissue rheology and lead to new diagnostic strategies. Attenuation is difficult to measure in acoustic radiation force elastography because the shear-wave amplitude decreases due to a combination of diffraction and viscous attenuation. Diffraction correction requires assuming a cylindrical wavefront and an isotropic propagation medium, which may not be the case in some applications. In this paper, the frequency-shift method, used in ultrasound imaging and seismology, was adapted for shear-wave attenuation measurement in elastography. This method is not sensitive to diffraction effects. For a linear frequency dependence of the attenuation, a closed-form relation was obtained between the decrease in the peak frequency of the gamma-distributed wave amplitude spectrum and the attenuation coefficient of the propagation medium. The proposed method was tested against a plane-wave reference method in homogeneous agar–gelatin phantoms with 0%, 10%, and 20% oil concentrations, and hence different attenuations of 0.117, 0.202, and 0.292 $\text {Np}\cdot \text {m}^{-1}$ /Hz, respectively. Applicability to biological tissues was demonstrated with two ex vivo porcine liver samples (0.79 and 1.35 $\text {Np} \,\cdot \, \text {m}^{-1}$ /Hz) and an in vivo human muscle, measured along (0.43 $\text {Np}\,\cdot \, \text {m}^{-1}$ /Hz) and across (1.77 $\text {Np}\cdot \text {m}^{-1}$ /Hz) the tissue fibers. In all cases, the data supported the assumptions of a gamma-distributed spectrum for the source and linear frequency attenuation for the tissue. This method provides tissue attenuation, which is relevant diagnostic information to model viscosity, in addition to shear-wave velocity used to assess elasticity. Data processing is simple and could be performed automatically in real time for clinical applications.

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27 citations


Cites background from "Measurement of Viscoelastic Propert..."

  • ...viscoelastic phantoms [38], [44], and may allow obtaining a...

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Journal ArticleDOI
Zhongkui Wang1, Lijuan Wang1, Van Anh Ho1, S. Morikawa2  +1 moreInstitutions (2)
TL;DR: It is found that the Voigt model can simulate the force behaviors of a fingertip phantom but has difficulty to reproduce the force relaxation behavior of a human fingertip, so a parallel five-parameter physical model is introduced to solve this problem.

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Abstract: A 3-D nonhomogeneous finite-element (FE) dynamic model of a primate fingertip is developed in this paper based on magnetic resonance (MR) imaging measurements for better understanding the mechanism of human finger sensation. The geometries of a human fingertip are measured using an MR system, and a series of 2-D images is obtained. Utilizing a boundary tracking method, boundaries of the fingertip and distal phalanx are tracked from each image slice and a set of boundary nodes is generated to construct a 3-D tetrahedral mesh of the fingertip. The 3-D mesh is then utilized to formulate a nonhomogeneous FE dynamic model for simulating the fingertip behaviors. The constitutive model, which consists of elastic and viscous elements, is employed to govern the dynamic behaviors of individual tetrahedral FE. The FE model is further extended to deal with contact interaction between the fingertip and an external instrument. Differing with conventional fingertip models, the model presented in this paper is able to not only better represent internal and external geometries of a human fingertip but also take the tissue viscosity into consideration. Simulation and experiments are performed with both a human finger and a fingertip phantom under different indentation operations. We found that the Voigt model can simulate the force behaviors of a fingertip phantom but has difficulty to reproduce the force relaxation behavior of a human fingertip. We have therefore introduced a parallel five-parameter physical model to solve this problem.

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25 citations


Cites background from "Measurement of Viscoelastic Propert..."

  • ...In order to accurately mimic the behaviors of human fingertip, high-quality phantoms are required, such as the polyacrylamide-based tissue-mimicking phantom presented in [30]....

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"Measurement of Viscoelastic Propert..." refers methods in this paper

  • ...The measurements of these properties were done using external quasi-static [11] or dynamic [17] excitations or using ultrasound-generated radiation force [18], [19]....

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  • ...Ultrasound elastography is a method to identify pathological changes by measuring elastic properties of tissues [11], [16] using ultrasound....

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  • ...As opposed to a procedure involving human intervention, there are several techniques that use phase-sensitive imaging modalities such as ultrasound [11]–[13] and magnetic resonance imaging [14], [15] to image the mechanical properties of soft tissues....

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Journal ArticleDOI

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Marc A. Meyers1, Krishan Kumar Chawla2Institutions (2)
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No. of citations received by the Paper in previous years
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