The influence of viscosity on the shear strain remotely induced by focused ultrasound in viscoelastic media (original) (raw)
Related papers
Shear wave elasticity imaging: a new ultrasonic technology of medical diagnostics
Ultrasound in Medicine & Biology, 1998
Shear wave elasticity imaging (SWEI) is a new approach to imaging and characterizing tissue structures based on the use of shear acoustic waves remotely induced by the radiation force of a focused ultrasonic beam. SWEI provides the physician with a virtual "finger" to probe the elasticity of the internal regions of the body. In SWEI, compared to other approaches in elasticity imaging, the induced strain in the tissue can be highly localized, because the remotely induced shear waves are attenuated fully within a very limited area of tissue in the vicinity of the focal point of a focused ultrasound beam. SWEI may add a new quality to conventional ultrasonic imaging or magnetic resonance imaging. Adding shear elasticity data ("palpation information") by superimposing color-coded elasticity data over ultrasonic or magnetic resonance images may enable better differentiation of tissues and further enhance diagnosis. This article presents a physical and mathematical basis of SWEI with some experimental results of pilot studies proving feasibility of this new ultrasonic technology. A theoretical model of shear oscillations in soft biological tissue remotely induced by the radiation force of focused ultrasound is described. Experimental studies based on optical and magnetic resonance imaging detection of these shear waves are presented. Recorded spatial and temporal profiles of propagating shear waves fully confirm the results of mathematical modeling. Finally, the safety of the SWEI method is discussed, and it is shown that typical ultrasonic exposure of SWEI is significantly below the threshold of damaging effects of focused ultrasound. © 1998 World Federation for Ultrasound in Medicine & Biology.
Study of viscous and elastic properties of soft tissues using supersonic shear imaging
IEEE Symposium on Ultrasonics, 2003, 2003
Supersonic Shear imaging (SSI) is a new ultrasound based technique for real time visualization of soft tissue viscoelastic properties. Using ultrasound focused beams, it is possible to remotely generate inside the body mechanical sources radiating low frequency shear waves [1][2][3]. SSI is based on the ultrasonic generation of a shear source moving at a supersonic speed inside the body. In a complete analogy with the "sonic boom" created by a supersonic aircraft, the resulting shear waves will constructively interfere along a Mach cone, creating two intense plane waves. These plane shear waves propagate through the medium and are progressively distorted by tissue mechanical inhomogeneities. The ultrafast scanner developed in our laboratory (5000 images/s) is able to generate this supersonic source and image, in real time, the propagation of the resulting shear waves. Using inversion algorithms, viscosity and elasticity maps of the medium can be deduced from this shear wave propagation movie. Creating such a supersonic regime enables quantitative tissue elasticity mapping in less than 20 ms, even in strongly viscous medium like breast or liver. Results validating SSI for quantitative shear elasticity mapping in heterogeneous tissue mimicking phantoms are presented. Detection of in vitro thermally-induced lesions on fresh tissue samples is shown. In vivo tests made on healthy volunteers show the potential clinical applicability of SSI for breast cancer detection. Finally, viscosity mapping using SSI has been studied theoretically and experimentally. Based on a Voigt model, simulations in different viscous and elastic media were compared and fitted to in vitro experiments. Using this theoretical background, viscosity maps using SSI were for the first time derived in viscoelastic phantoms.
Japanese Journal of Applied Physics
It is important to evaluate the viscoelasticity of muscle for assessment of its condition. However, quantitative and noninvasive diagnostic methods have not yet been established. In our previous study, we developed a method, which used ultrasonic acoustic radiation forces irradiated from two opposite horizontal directions, for measurement of the viscoelasticity. Using two continuous wave ultrasounds, an object can be actuated with an ultrasonic intensity, which is far lower (0.9 W/cm 2) than that in the case of the conventional acoustic radiation force impulse (ARFI) method. In the present study, in vitro experiments using phantoms made of polyurethane rubber and porcine muscle tissue embedded in a gelatin block were conducted. We actuated phantoms by ultrasonic radiation force and measured the propagation velocity of the generated shear wave inside the phantoms using a diagnostic ultrasound system. The viscoelasticities of phantoms were estimated by fitting a viscoelastic model, i.e., the Voigt model, to the frequency characteristic of the measured shear wave propagation speed. In the mechanical tensile test, a softer polyurethane phantom exhibited a lower elasticity and a higher viscosity than a polyurethane phantom with a higher elasticity and a lower viscosity. The viscoelasticity measured by ultrasound showed the same tendency as that in the tensile test. Furthermore, the viscoelasticity of the phantom with porcine muscular tissue was measured in vitro, and the estimated viscoelasticity agreed well with that reported in the literature. These results show the possibility of the proposed method for noninvasive and quantitative assessment of the viscoelasticity of biological soft tissue.
Ultrasound imaging of soft tissue shear viscosity
IEEE Symposium on Ultrasonics, 2003
Changes in tissue mechanical (elasticity, viscosity, etc.) properties are often associated with tissue pathology. In this paper, we present an ultrasound method capable of imaging the shear viscosity of soft tissue. This method is based on the measurement of creep function where tissue viscosity can be assessed by measuring slowly varying residual mechanical deformations induced by steady external forces rapidly applied at the surface. A finite element analysis of internal deformations of inhomogeneous viscoelastic medium was performed to investigate the capabilities of viscosity imaging. Then the ultrasound measurements of creep function were performed in the tissue sample (bovine muscle) to remotely assess viscoelastic properties of the tissue. The results of numerical and experimental studies suggest that time-dependent deformations can be measured with ultrasound to estimate and image both tissue elasticity and viscosity.
Shearwave dispersion ultrasound vibrometry (SDUV) for measuring tissue elasticity and viscosity
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2009
Characterization of tissue elasticity (stiffness) and viscosity has important medical applications because these properties are closely related to pathological changes. Quantitative measurement is more suitable than qualitative measurement (i.e., mapping with a relative scale) of tissue viscoelasticity for diagnosis of diffuse diseases where abnormality is not confined to a local region and there is no normal background tissue to provide contrast. Shearwave dispersion ultrasound vibrometry (SDUV) uses shear wave propagation speed measured in tissue at multiple frequencies (typically in the range of hundreds of Hertz) to solve quantitatively for both tissue elasticity and viscosity. A shear wave is stimulated within the tissue by an ultrasound push beam and monitored by a separate ultrasound detect beam. The phase difference of the shear wave between 2 locations along its propagation path is used to calculate shear wave speed within the tissue. In vitro SDUV measurements along and across bovine striated muscle fibers show results of tissue elasticity and viscosity close to literature values. An intermittent pulse sequence is developed to allow one array transducer for both push and detect function. Feasibility of this pulse sequence is demonstrated by in vivo SDUV measurements in swine liver using a dual transducer prototype simulating the operation of a single array transducer.
Viscoelasticity Imaging of Biological Tissues and Single Cells Using Shear Wave Propagation
Frontiers in Physics, 2021
Changes in biomechanical properties of biological soft tissues are often associated with physiological dysfunctions. Since biological soft tissues are hydrated, viscoelasticity is likely suitable to represent its solid-like behavior using elasticity and fluid-like behavior using viscosity. Shear wave elastography is a non-invasive imaging technology invented for clinical applications that has shown promise to characterize various tissue viscoelasticity. It is based on measuring and analyzing velocities and attenuations of propagated shear waves. In this review, principles and technical developments of shear wave elastography for viscoelasticity characterization from organ to cellular levels are presented, and different imaging modalities used to track shear wave propagation are described. At a macroscopic scale, techniques for inducing shear waves using an external mechanical vibration, an acoustic radiation pressure or a Lorentz force are reviewed along with imaging approaches proposed to track shear wave propagation, namely ultrasound, magnetic resonance, optical, and photoacoustic means. Then, approaches for theoretical modeling and tracking of shear waves are detailed. Following it, some examples of applications to characterize the viscoelasticity of various organs are given. At a microscopic scale, a novel cellular shear wave elastography method using an external vibration and optical microscopy is illustrated. Finally, current limitations and future directions in shear wave elastography are presented.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000
An ultrasound-based method to locally assess the shear modulus of a medium is reported. The proposed approach is based on the application of an impulse acoustic radiation force to an inhomogeneity in the medium and subsequent monitoring of the spatio-temporal response. In our experimental studies, a short pulse produced by a 1.5-MHz highly focused ultrasound transducer was used to initiate the motion of a rigid sphere embedded into an elastic medium. Another 25 MHz focused ultrasound transducer operating in pulse-echo mode was used to track the displacement of the sphere. The experiments were performed in gel phantoms with varying shear modulus to demonstrate the relationship between the displacement of the sphere and shear modulus of the surrounding medium. Because the magnitude of acoustic force applied to sphere depends on the acoustic material properties and, therefore, cannot be used to assess the absolute value of shear modulus, the temporal behavior of the displacement of the sphere was analyzed. The results of this study indicate that there is a strong correlation between the shear modulus of a medium and spatio-temporal characteristics of the motion of the rigid sphere embedded in this medium.
Ultrasound in medicine & biology, 2010
The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue because the muscle is an anisotropic, viscoelastic and dynamic medium. In this article, these mechanical properties are characterized for the brachialis muscle in vivo using a noninvasive ultrasound-based technique. This supersonic shear imaging technique combines an ultra-fast ultrasonic system and the remote generation of transient mechanical forces into tissue via the radiation force of focused ultrasonic beams. Such an ultrasonic radiation force is induced deep within the muscle by a conventional ultrasonic probe and the resulting shear waves are then imaged with the same probe (5 MHz) at an ultra-fast framerate (up to 5000 frames/s). Local tissue velocity maps are obtained with a conventional speckle tracking technique and provide a full movie of the shear wave propagation through the entire muscle. Shear wave group velocities are then estimated using a time of flight algorithm. Thi...
Because tissues consist of solid and fluid materials, their mechanical properties should be characterized in terms of both elasticity and viscosity. Although the elastic properties of tissue-mimicking phantoms have been extensively studied and well characterized in commercially available phantoms, their viscous properties have not been fully investigated. In this article, a set of 14 tissue-mimicking phantoms with different concentrations of gelatin and castor oil were fabricated and characterized in terms of acoustic and viscoelastic properties. The results indicate that adding castor oil to gelatin phantoms decreases shear modulus, but increases shear wave dispersion. For 3% gelatin phantoms containing 0%, 10%, 20% and 40% oil, the measured shear moduli are 2.01 ± 0.26, 1.68 ± 0.25, 1.10 ± 0.22 and 0.88 ± 0.17 kPa, and the Voigt-model coupled shear viscosities are 0.60 ± 0.11, 0.89 ± 0.07, 1.05 ± 0.11 and 1.06 ± 0.13 Pa$s, respectively. The results also confirm that increasing the gelatin concentration increases shear modulus. For phantoms containing 3%, 4%, 5%, 6% and 7% gelatin, the measured shear moduli are 2.01 ± 0.26, 3.10 ± 0.34, 4.18 ± 0.84, 8.05 ± 1.00 and 10.24 ± 1.80 kPa at 0% oil and 1.10 ± 0.22, 1.97 ± 0.20, 3.13 ± 0.63, 4.60 ± 0.60 and 8.43 ± 1.39 kPa at 20% oil, respectively. The phantom recipe developed in this study can be used in validating ultrasound shear wave elastography techniques for soft tissues. (