Lumbar multifidus layers stiffness at L5-S1 level in prone and sitting posture measured by shear wave elastography.

BACKGROUND: Multifidus is an important lumbar muscle with distinct superficial and deep fibers responsible for torque production and stabilization, respectively. Its mechanical properties change when transitioning from lying to sitting positions, necessitating enhanced stability. It holds crucial clinical relevance to assess these layers separately, especially in the sitting posture, which demands increased neuromuscular control compared to the prone position. OBJECTIVE: To compare lumbar multifidus stiffness in lying versus sitting postures, analyzing both superficial and deep layers. METHODS: Supersonic Shear Imaging captured elastographic images from 26 asymptomatic volunteers in prone and seated positions. RESULTS: Left multifidus shear modulus in lying: 5.98 ± 1.80/7.96 ± 1.59 kPa (deep/superficial) and sitting: 12.58 ± 4.22/16.04 ± 6.65 kPa. Right side lying: 6.08 ± 1.97/7.80 ± 1.76 kPa and sitting: 13.25 ± 4.61/17.95 ± 7.12 kPa. No side differences (lying p= 0.99, sitting p= 0.43). However, significant inter-postural differences occurred. CONCLUSION: Lumbar multifidus exhibits increased stiffness in sitting, both layers affected, with superior stiffness in superficial versus deep fibers. Applying these findings could enhance assessing multifidus stiffness changes, for classifying tension-induced low back pain stages.

Effect of Reducing the Size and Number of Faces of Polyhedral Specimen on Wood Characterization by Ultrasound.

The complete characterization of wood, with the determination of the 12 elastic constants that represent its orthotropy, is greatly relevant in applications employing structural calculation software programs. Ultrasound allows for such characterization with relative simplicity when compared to other methods. The polyhedron is considered the most appropriate specimen format for allowing the 12 constants to be calculated with a single specimen, and the traditionally used one is the 26-sided polyhedron, which, to be produced manually with more precision in directing the main directions of the wood, needs larger faces. The accuracy of this technique tends to be reduced when increasing the growth rings' inclination since the waves deviate from the main directions of orthotropy. This research aimed to verify whether it is possible to reduce the polyhedra dimension without affecting the results of the elastic parameters obtained in wood characterization by ultrasound. The results indicate that the dimension of the polyhedron can be reduced without prejudice to the results of the elastic parameters obtained by the ultrasound test and that, in the manual production process of the specimen, the best way to make this reduction is to eliminate the faces unused in the test, changing the polyhedron to 18 faces instead of 26. Reducing the number of faces simplifies the manufacturing process and thus increases the possibility of producing specimens with straighter growth rings and better-directed symmetry axes.

Viscoelastic Properties of Acellular Matrices of Porcine Esophageal Mucosa and Comparison with Acellular Matrices of Porcine Small Intestine Submucosa and Bovine Pericardium.

The aim of this study was to compare the viscoelastic properties of a decellularized mesh from the porcine esophagus, prepared by our group, with two commercial acellular tissues derived from porcine small intestine submucosa and bovine pericardium for use in medical devices. The tissues' viscoelastic properties were characterized by creep tests in tension, applying the load in the direction of the fibers or the transverse direction, and also by dynamic-shear mechanical tests between parallel plates or in tension at frequencies between 0.1 and 35 Hz. All the tests were performed in triplicate at a constant temperature of 37 °C immersed in distilled water. The tissues' surface and cross-sectional microstructure were observed by scanning electron microscopy (SEM) to characterize the orientation of the fibers. The matrices of the porcine esophagus present an elastic modulus in the order of 60 MPa when loaded in the longitudinal direction while those of the porcine intestine submucosa and bovine pericardium have an elastic modulus below 5 MPa. Nevertheless, the shear modulus of bovine pericardium nearly triplicates that of the esophageal matrix. The viscoelasticity of decellularized esophageal mucosa is characterized by a fast change in the creep compliance with time. The slope of the creep curve in the double logarithmic plot is twice that of the control samples. These results are consistent with the microstructure observed under electron microscopy regarding the orientation of the fibers that make up the matrices.

Plasmodium falciparum maturation across the intra-erythrocytic cycle shifts the soft glassy viscoelastic properties of red blood cells from a liquid-like towards a solid-like behavior.

The mechanical properties of erythrocytes have been investigated by different techniques. However, there are few reports on how the viscoelasticity of these cells varies during malaria disease. Here, we quantitatively map the viscoelastic properties of Plasmodium falciparum-parasitized human erythrocytes. We apply new methodologies based on optical tweezers to measure the viscoelastic properties and defocusing microscopy to measure the erythrocyte height profile, the overall cell volume, and its form factor, a crucial parameter to convert the complex elastic constant into complex shear modulus. The storage and loss shear moduli are obtained for each stage of parasite maturation inside red blood cells, while the former increase, the latter decrease. Employing a soft glassy rheology model, we obtain the power-law exponent for the storage and loss shear moduli, characterizing the soft glassy features of red blood cells in each parasite maturation stage. Ring forms present a liquid-like behavior, with a slightly lower power-law exponent than healthy erythrocytes, whereas trophozoite and schizont stages exhibit increasingly solid-like behaviors. Finally, the surface elastic shear moduli, low-frequency surface viscosities, and shape recovery relaxation times all increase not only in a stage-dependent manner but also when compared to healthy red blood cells. Overall, the results call attention to the soft glassy characteristics of Plasmodium falciparum-parasitized erythrocyte membrane and may provide a basis for future studies to better understand malaria disease from a mechanobiological perspective.

Supersonic Shear Imaging Elastography in Skeletal Muscles: Relationship Between In Vivo and Synthetic Fiber Angles and Shear Modulus.

OBJECTIVES: To verify a relationship between the pennation angle of synthetic fibers and muscle fibers with the shear modulus (µ) generated by Supersonic shear imaging (SSI) elastography and to compare the anisotropy of synthetic and in vivo pennate muscle fibers in the x2 -x3 plane (probe perpendicular to water surface or skin). METHODS: First, the probe of Aixplorer ultrasound scanner (v.9, Supersonic Imagine, Aix-en-Provence, France) was placed in 2 positions (parallel [aligned] and transverse to the fibers) to test the anisotropy in the x2 -x3 plane. Subsequently, it was inclined (x1 -x3 plane) in relation to the fibers, forming 3 angles (18.25 °, 21.55 °, 36.86 °) for synthetic fibers and one (approximately 0 °) for muscle fibers. RESULTS: On the x2 -x3 plane, µ values of the synthetic and vastus lateralis fibers were significantly lower (P < .0001) at the transverse probe position than the longitudinal one. In the x1 -x3 plane, the µ values were significantly reduced (P < .0001) with the probe angle increasing, only for the synthetic fibers (approximately 0.90 kPa for each degree of pennation angle). CONCLUSIONS: The pennation angle was not related to the µ values generated by SSI elastography for the in vivo lateral head of the gastrocnemius and vastus lateralis muscles. However, a µ reduction with an angle increase in the synthetic fibers was observed. These findings contribute to increasing the applicability of SSI in distinct muscle architecture at normal or pathologic conditions.

Semitendinosus and patellar tendons shear modulus evaluation by supersonic shearwave imaging elastography.

PURPOSE: Shear modulus (µ) is directly correlated to the tissue stiffness and can predict the tendon ultimate force to failure. With the knee extended 0° (K0), semitendinosus tendon (ST) is tensioned while patellar tendon (PT) is relaxed. At 80o , knee flexion (K80) tendons present an opposite stress pattern; however, the relation between ST and PT µ in both situations was not studied yet. METHOD: We accessed the µ of the ST and PT at 0o and 80o knee flexion by supersonic shear wave imaging (SSI) elastography from 18 healthy males. Relative µ indexes were calculated for relaxed and tensioned conditions. RESULT: The average µ for ST was µST-K0  = 197·62 ± 31·93 kPa and µST-K80  = 77·76 ± 30·08. For TP, values were µTP-K0  = 23·45 ± 5·89 and µTP-K80  = 113·92 ± 57·23 kPa. Relative µ indexes were calculated for relaxed (IR = µST-K80 /µTP-K0 ) and tensioned conditions (IT = µST-K0 /µPT-K80 ). The relative µ indexes were IR = 3·63 ± 1·50 and IT = 2·00 ± 0·96 (P<0·05). CONCLUSION: Semitendinosus tendon µ was significantly higher than PT µ in both tensioned and relaxed positions. This can predict a higher ultimate force to failure and a less elastic behaviour in ST grafts when compared to PT grafts. This new parameter could aid physicians in graft choice previous to anterior cruciate ligament reconstruction.

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.

Characterizing a Brazilian sanitary landfill using geophysical seismic techniques.

Two different geophysical techniques, namely crosshole and multichannel analysis of surface waves - MASW, were applied to investigate the mechanical response of Municipal Solid Waste buried under humid, subtropical climate. Direct investigations revealed that the buried waste was composed mainly of soil-like material (51%) and plastics (31%) with moisture content average values of 43% near the surface and 53% after around 11m depth. Unit weight varied between 9kN/m(3) and 15kN/m(3). Seismic investigation of the landfill yielded shear wave velocities (VS) estimated from the crosshole tests ranging from 92 to 214m/s, while compression wave velocities (VP) ranged from 197 to 451m/s. Both velocities were influenced by vertical confining stress and thus tended to increase with depth. VS calculated from MASW tests were lower than the ones calculated from the crosshole tests, probably due to the different frequencies used in the tests. The results of both methods tended to configure a lower bound to the values reported in the technical literature in general, as expected for low compaction waste with small amounts of cover soil. Although VS did not show abrupt changes with depth, VP profile distribution combined with direct investigations results, such as temperature, in-place unit weight and moisture content, suggest that the waste body could be divided into two strata. The lower one is poorly drained and shows higher moisture content, as a consequence of the operational techniques used in the first years, while the upper stratum is probably related to a better drained waste stratum, resulting from the improvement of operational standards and increase in drainage facilities throughout the years.