Assessment of the mechanical properties of the muscle-tendon unit by supersonic shear wave imaging elastography: a review

This review aimed to describe the state of the art in muscle-tendon unit (MTU) assessment by supersonic shear wave imaging (SSI) elastography in states of muscle contraction and stretching, during aging, and in response to injury and therapeutic interventions. A consensus exists that MTU elasticity increases during passive stretching or contraction, and decreases after static stretching, electrostimulation, massage, and dry needling. There is currently no agreement regarding changes in the MTU due to aging and injury. Currently, the application of SSI for the purpose of diagnosis, rehabilitation, and physical training remains limited by a number of issues, including the lack of normative value ranges, the lack of consensus regarding the appropriate terminology, and an inadequate understanding of the main technical limitations of this novel technology.

Ultrasonic method of microvibration detection: part II - additional processing method and applications

Abstract Introduction In the last 28 years, the scientific community has been using elastography to evaluate the mechanical properties of biological tissue. The aim of this work was the optimization of the UDmV method, presented in Part I of the series, by means of modifying the technique employed to generate the reference sine and cosine functions, used for phase-quadrature demodulation, and determining how this modification improved the performance of the method. Additionally, the UDmV was employed to characterize the acoustic and mechanical properties of a 7% gelatin phantom. Methods A focused transducer, T F, with a nominal frequency of 2.25 MHz, was used to induce the shear waves, with frequency of 97.644 Hz. Then, the modified UDmV method was used to extract the phase and quadrature components from ultrasonic RF echo-signals collected from four positions along the propagation path of the shear wave, which allowed the investigation of the medium vibration caused by wave propagation. The phase velocity, c s, and attenuation, α s, of the phantom were measured and employed in the calculation of shear modulus, μ, and viscosity, η. Results The computational simulation demonstrated that the modification in UDmV method resulted in more accurate and precise estimates of the initial phases of the reference sinusoidal functions used for phase-quadrature demodulation. The values for c s and μ of 1.31 ± 0.01 m·s-1 and 1.66 ± 0.01 kPa, respectively, are very close to the values found in the literature (1.32 m·s-1 and 1.61 kPa) for the same material. Conclusion The UDmV method allowed estimating of the acoustic and viscoelastic parameters of phantom.

Limitations and artifacts in shear-wave elastography of the liver

Recent studies have shown that real-time, two-dimensional shear-wave elastography (2D-SWE) can monitor liver fibrosis by measuring tissue elasticity (i.e., elastic modulus). Two clinical studies of 2D-SWE in the liver have shown that there are several practical issues that can compromise quantitation of liver tissue elasticity. Both general ultrasound (US) limitations and limitations in the 2D-SWE method itself resulted in significant variability in estimated liver elasticity. The most common US limitations were: poor acoustic window, limited penetration, and rib/lung shadows. The most common 2D-SWE limitations were: reverberations under the liver capsule, respiratory/cardiac motion, and vessel pulsation/loss of SWE signal. Based on these studies, scan protocols have been optimized to minimize the influence of these limitations on liver elasticity quantification. These refined protocols should move non-invasive SWE closer to becoming the preferred tool to diagnose and manage many chronic diseases of the liver.

Quantification of shear modulus in in vitro porcine myocardium using real-time shear wave elastography / 中华超声影像学杂志

Objective To investigate in vitro porcine myocardial shear modulus using real-time shear wave elastography.Methods Shear wave elastography was used on four in vitro porcine hearts.The probe was placed parallel to the long or short-axis of the heart on the anterior wall of the left ventricle,and myocardial shear modulus were measured in subepicardial,middle,subendocardial layers,respectively.Results Shear modulus of subepicardial,middle,subendocardial myocardium were (46.04 ± 17.07)kPa,(87.70 ± 29.67) kPa,( 115.73 ± 30.04) kPa,respectively,when the probe was placed parallel to the long-axis of the heart; whereas those were (78.71 ± 26.48) kPa,(77.08 ± 34.00)kPa,(70.69 ± 41.38) kPa,respectively,when the probe was placed parallel to the short-axis of the heart.Conclusions By using realtime shear wave elastography,the shear modulus values measured in subepicardial,middle,subendocardial myocardium of the left ventricle are different,even myocardium in the same location appears different shear modulus values when the probe orientation are different.

Shear modulus measurement of biological tissues based on Zener model / 医用生物力学

Objective To measure the shear modulus of biological tissues by using Zener model so as to overcome the limitation of Voigt model-based ultrasound vibrometry, and to provide effective approaches of tissue characterization. Methods The mechanical constitutive relation-based shear wave propagation velocity formula was utilized to estimate the shear modulus in terms of the velocities at multiple frequencies via mathematical methods. To obtain shear wave velocities in different objects, experiments were conducted by using different consistencies-based gelatin models and thermally damaged porcine livers as subjects, in which shear waves were induced by ultrasound radio forces. Results Voigt and Zener models were utilized to fit the velocities respectively. The Zener model exhibited higher fitting accuracy than the Voigt model, and the shear modulus could well distinguish gelatin models with different consistencies or porcine livers of different damage degrees. Conclusions The method in this paper provides a potential means of measuring the shear modulus of biological tissues non invasively, which is very promising for tissue characterization and disease diagnosis in medicine.

The change of the initial dynamic visco-elastic modulus of composite resins during light polymerization / 대한치과보존학회지

The aim of this study was to measure the initial dynamic modulus changes of light cured composites using a custom made rheometer. The custom made rheometer consisted of 3 parts: (1) a measurement unit of parallel plates made of glass rods, (2) an oscillating shear strain generator with a DC motor and a crank mechanism, (3) a stress measurement device using an electromagnetic torque sensor. This instrument could measure a maximum torque of 2Ncm, and the switch of the light-curing unit was synchronized with the rheometer. Six commercial composite resins [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF)] were investigated. A dynamic oscillating shear test was undertaken with the rheometer. A certain volume (14.2 mm3) of composite was loaded between the parallel plates, which were made of glass rods (3 mm in diameter). An oscillating shear strain with a frequency of 6 Hz and amplitude of 0.00579 rad was applied to the specimen and the resultant stress was measured. Data acquisition started simultaneously with light curing, and the changes in visco-elasticity of composites were recorded for 10 seconds. The measurements were repeated 5 times for each composite at 25+/-0.5degrees C. Complex shear modulus G*, storage shear modulus G', loss shear modulus G" were calculated from the measured strain-stress curves. Time to reach the complex modulus G* of 10 MPa was determined. The G* and time to reach the G* of 10 MPa of composites were analyzed with One-way ANOVA and Tukey's test (alpha = 0.05). The results were as follows. 1. The custom made rheometer in this study reliably measured the initial visco-elastic modulus changes of composites during 10 seconds of light curing. 2. In all composites, the development of complex shear modulus G* had a latent period for 1~2 seconds immediately after the start of light curing, and then increased rapidly during 10 seconds. 3. In all composites, the storage shear modulus G' increased steeper than the loss shear modulus G" during 10 seconds of light curing. 4. The complex shear modulus of Z1 was the highest, followed by CF, Z2, Z3, TC and DF the lowest. 5. Z1 was the fastest and DF was the slowest in the time to reach the complex shear modulus of 10 MPa.

Magnetic Resonance Elastography: Preliminary Experimental Study / 中国医学物理学杂志

Objective: To study magnetic resonance elastography (MRE) technique. Methods: An external force actuator was developed, the imaging pulse sequence of MRE was designed,and tissue simulating phantoms were constructed. The actuator controlled by the pulse sepuence produced shear waves at low frequency on the surface of the phantoms. A modified gradient echo sequence was developed with motion sensitizing gradient (MSG)imposed along X,Y or Z direction.Cyclic displacement within the medium induced by shear waves caused a measurable phase shift in the received MR signal.From the measured phase shift,the displacement at each voxel could be calculated,and the propatating shear waves within the medium were directly imaged. By adjusting the phase offsets,the dynamic propagation of shear waves in a wave cycle was obtained.The phase images were processed to aquire quantitative elasticity image using local frequency estimation(LFE)method. The experiments were implemented with 1.0% and 1.5% tissue simulating agarose gel. Shear waves at frequency of 150 Hz,200 Hz,250 Hz,and 300 Hz were applied. Results: The phase images of MRE directly imaged the propagating shear waves within the phantoms.The wavelength of shear waves varied with the change of exciting frequency and stiffness of the phantoms. The wavelength of shear waves was exactly proportional to the frequency and stiffness of the phantom. The contrast of elasticity in agarose gel with two concentrations was clearly demonstrated on elasticity images.Conclusion: The phase images of MRE can directly visualize the propagation of shear waves in the medium. The elasticity image of MRE can quantitatively image the elastic modulus of the medium

Rheological properties of resin composites according to the change of monomer and filler compositions / 대한치과보존학회지

OBJECTIVES: The aim of this study was to investigate the effect of monomer and filler compositions on the rheological properties related to the handling characteristics of resin composites. METHODS: Resin matrices that Bis-GMA as base monomer was blended with TEGDMA as diluent at various ratio were mixed with the Barium glass (0.7 um and 1.0 um), 0.04 um fumed silica and 0.5 um round silica. All used fillers were silane treated. In order to vary the viscosity of experimental composites, the type and content of incorporated fillers were changed. Using a rheometer, a steady shear test and a dynamic oscillatory shear test were used to evaluate the viscosity (eta) of resin matrix, and the storage shear modulus (G'), the loss shear modulus (G"), the loss tangent (tandelta) and the complex viscosity (eta*) of the composites as a function of frequency omega = 0.1-100 rad/s. To investigate the effect of temperature on the viscosity of composites, a temperature sweep test was also undertaken. RESULTS: Resin matrices were Newtonian fluid regardless of diluent concentration and all experimental composites exhibited pseudoplastic behavior with increasing shear rate. The viscosity of composites was exponentially increased with increasing filler volume%. In the same filler volume, the smaller the fillers were used, the higher the viscosities were. The effect of filler size on the viscosity was increased with increasing filler content. Increasing filler content reduced tandelta by increasing the G' further than the G". The viscosity of composites was decreased exponentially with increasing temperature.