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Journal ArticleDOI

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

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.
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.
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.
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.

186 citations

Journal ArticleDOI
TL;DR: In this paper, the transverse vibrational model of a viscous-fluid-conveying single-walled carbon nanotube (SWCNT) embedded in biological soft tissue is developed.
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.

81 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.
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.

40 citations


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

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

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Journal ArticleDOI
TL;DR: In this paper, the effects of the transverse shear deformation and rotary inertia are considered by utilizing the Timoshenko beam theory and considering a material length scale parameter for beam model.
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.

37 citations

Journal ArticleDOI
TL;DR: Glycerol dispersion in oil-based gels is proposed to modify the acoustic and elastic properties of copolymer-in-oil phantoms and opens the possibility of incorporating other oil-insoluble substances to control further properties of the phantom.
Abstract: Phantoms are important tools for image quality control and medical training. Many phantom materials have been proposed for ultrasound; most of them use water as the solvent, but these materials have disadvantages such as dehydration and low temporal stability if not properly stored. To overcome these difficulties, copolymer-in-oil gel was proposed as an inert and stable material; however, speed of sound for these materials is still lower than what is described for most biological tissues. Here, we propose the glycerol dispersion in oil-based gels to modify the acoustic and elastic properties of copolymer-in-oil phantoms. We manufactured copolymer-in-oil gels using styrene-ethylene/butylene-styrene (SEBS) in concentrations 8%–15%. We used 2 types of mineral oils with different viscosities. Glycerol was added in a volume fraction 0%–30% of the total amount of liquid. The acoustic ( i.e., speed of sound, attenuation and backscattering) and the mechanical ( i.e., density and Young's modulus) properties of the samples were within the range of values observed for soft tissues. The acoustic parameters of the samples were dependent on oil viscosity and glycerol concentration. The speed of sound ranged 1423 m/s – 1502 m/s, while the acoustic attenuation and the ultrasonic backscattering increased by adding glycerol. The density and the Young's moduli were less affected by the presence of glycerol. We conclude that glycerol can be used to control the acoustic parameters of copolymer-in-oil gels. Additionally, it opens the possibility of incorporating other oil-insoluble substances to control further properties of the phantom.

28 citations

References
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Journal ArticleDOI
TL;DR: Magnetic resonance elastography shows promise as a potential technique for 'palpation by imaging', with possible applications in tumor detection, characterization of disease, and assessment of rehabilitation (particularly in muscle).

1,062 citations


Additional excerpts

  • ...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
TL;DR: This book is the second edition of the first volume in a series of three volumes by Y. C. Fung on biomechanics that summarizes the application of an enormously wide spectrum of mechanics and thermodynamics to physiology and the engineering of biologically related problems.

1,025 citations


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

  • ...The basis for the development of these methods is that disease processes alter tissue elastic properties [1], [16]....

    [...]

  • ...Data available on the elastic properties of the tissues are limited to blood vessels, skeletal muscle, heart muscle, bone, and cartilage [1], [2]....

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  • ...cross-sectional area and measuring the force response [1], [7],...

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Journal ArticleDOI
TL;DR: Elastography has the potential to be useful in the evaluation of areas of shadowing on the sonogram and also may be helpful in the distinction of benign from malignant masses.
Abstract: PURPOSE: To determine the appearance of various breast lesions on elastograms and to explore the potential of elastography in the diagnosis of breast lesions. MATERIALS AND METHODS: A total of 46 breast lesions were examined with elastography. Patients underwent biopsy or aspiration of all lesions, revealing 15 fibroadenomas, 12 carcinomas, six fibrocystic nodules, and 13 other lesions. The elastogram was generated from radio-frequency data collected with use of a 5-MHz linear-array transducer. The elastogram and corresponding sonogram were evaluated by a single observer for lesion visualization, relative brightness, and margin definition and regularity. The sizes of the lesions at each imaging examination and at biopsy were recorded and compared. RESULTS: Softer tissues such as fat appear as bright areas on elastograms. Firm tissues, including parenchyma, cancers, and other masses, appear darker. The cancers were statistically significantly darker than fibroadenomas (P < .005) and substantially larger on...

980 citations


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

  • ...Clinical ultrasound elastography imaging of breast [12], [20] and thyroid [13], [21] has shown promising results in differentiating benign versus malignant lesions on the basis of elastographic contrast....

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Journal ArticleDOI
01 Mar 1999
TL;DR: The strain filter formalism and its utility in understanding the noise performance of the elastographic process is given, as well as its use for various image improvements.
Abstract: The basic principles of using sonographic techniques for imaging the elastic properties of tissues are described, with particular emphasis on elastography. After some preliminaries that describe some basic tissue stiffness measurements and some contrast transfer limitations of strain images are presented, four types of elastograms are described, which include axial strain, lateral strain, modulus and Poisson's ratio elastograms. The strain filter formalism and its utility in understanding the noise performance of the elastographic process is then given, as well as its use for various image improvements. After discussing some main classes of elastographic artefacts, the paper concludes with recent results of tissue elastography in vitro and in vivo.

837 citations


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

  • ...The basis for the development of these methods is that disease processes alter tissue elastic properties [1], [16]....

    [...]

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

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Journal ArticleDOI
TL;DR: Elastography is a promising imaging technique that can assist in the differential diagnosis of thyroid gland cancer, and the usefulness of these criteria was not considered to be high because of their low sensitivity.
Abstract: PURPOSE: To prospectively evaluate the elastographic appearance of thyroid gland tumors and explore the potential sensitivity and specificity of ultrasonographic (US) elastography for differentiating benign and malignant tumors, with histopathologic analysis as the reference standard. MATERIALS AND METHODS: The study was institutional review board approved, and each patient gave written informed consent. Fifty-two thyroid gland lesions (22 malignant, 30 benign) in 31 consecutive patients (six men, 25 women; mean age, 49.7 years ± 14.7 [standard deviation]) were examined with real-time elastography in the elasticity imaging mode implemented on a clinical US scanner modified for research. In addition, the radiofrequency echo data stored during US were exported from the scanner and used for off-line strain image reconstruction. All elastograms were evaluated for the lesion visibility, relative brightness, and margin regularity and definition by using a four-point scale. In addition, normal thyroid gland tiss...

621 citations


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

  • ...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....

    [...]

  • ...Clinical ultrasound elastography imaging of breast [12], [20] and thyroid [13], [21] has shown promising results in differentiating benign versus malignant lesions on the basis of elastographic contrast....

    [...]