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While skeletal muscle is often assumed to be structurally transversely isotropic, its mechanical anisotropy is not well characterized in vivo. Such in vivo characterization can be achieved using VisR ultrasound, a technique that provides information about the viscoelastic mechanical response of tissue. Specifically, VisR-derived Relative Elasticity (RE) provides directionally dependent information...
Degree of anisotropy (DoA) has been evaluated for clinical significance in several organs. In skeletal muscle, mechanical DoA has been shown to increase with passive extension, i.e. the shear modulus parallel to muscle fibers (μl) increases relative to that perpendicular (μt). Imaging such variations in DoA could facilitate diagnosing and monitoring muscle pathologies. We have previously demonstrated...
Renal parenchyma is strongly anisotropic; mechanical properties differ along versus across nephron alignment. In this work, the feasibility of interrogating such directional differences in mechanical property using ARFI is investigated. We hypothesize that: 1) the ratio of ARFI peak displacements (PDs) achieved with the long axis of an asymmetrical ARF PSF oriented along versus across nephron alignment...
Structure-property relationships in bulk materials can be important in establishing sensing methods to assess the state of material microstructure. This is particularly true for nuclear graphites since these materials can become oxidized under service conditions and the structural integrity must be confirmed during the lifetime of the material to ensure proper functioning of the reactor core. Many...
Many tissues, including muscle, can be described as transversely isotropic (TI) with an axis of symmetry (AoS) perpendicular to a plane of isotropy. Mechanical properties differ along versus across the AoS. We have previously shown that the degree of difference, or the ‘degree of anisotropy (DoA)’, can be assessed as the ratio of ARFI-induced peak displacements (PDs) achieved when the long axis of...
Cortical bone is an anisotropic material with hierarchical structure whose elastic properties are described at different length scales. At millimeter-scale, the whole set of stiffness tensor can be conveniently measured by resonant ultrasound spectroscopy (RUS). At microscopic-scale, micro-indentation and scanning acoustic microscopy are often used to quantify tissue matrix elastic properties. However,...
Previous studies have reported that shear wave speed along muscle fibers is distinct from the speed across the fibers. Therefore, the shear speed may be a sensitive method to determine muscle fiber orientation in vivo. The purpose of this study is to develop a reproducible method to determine anisotropy in muscle fibers using Shear Wave Elastography (SWE). This technique was used to study myofascial...
In Duchenne muscular dystrophy (DMD), muscle fiber necrosis and subsequent progressive replacement of muscle by fibrous tissue and fat impacts the degree of anisotropy (DoA) in mechanical properties. Mechanical DoA can be assessed in skeletal muscle using Viscoelastic Response (VisR) ultrasound. We hypothesize that in vivo VisR DoA measures in the rectus femoris (RF) muscles of boys with DMD statistically...
Human cortical bone is an anisotropic material, although isotropic stiffness is generally assumed in most finite element analysis. Detailed information about the anisotropic stiffness at a mesoscopic (mm) scale would improve our understanding of bone's macroscopic mechanical properties. In this work, we report on the anisotropic stiffness of human cortical bone from different sites, and the variation...
Articular cartilage is composed of cartilage cells and extracellular matrix (mainly collagen type II and proteoglycan). When stress is applied, the cartilage releases water and the stress is distributed [1]. The extra-cellular matrix structure is important to perform normal cartilaginous functions. It is then important to evaluate the elasticity and anisotropy of the cartilage, in addition to the...
The non-pregnant cervix is composed of layers of pseudo-aligned collagen wrapped circumferentially around the cervical canal. Studies in rodents have shown that this structure disorganizes and breaks down throughout normal pregnancy. There is evidence to suggest that layered, pseudo-aligned collagen fibers in the non-pregnant cervix induce an angle-dependence (anisotropy) in backscattered ultrasound...
The doping of liquid crystals (LCs) with carbon nanotubes and magnetic nanoparticles have attracted wide interest in many areas of science, technology and medicine. LCs occur as additional, thermodynamically stable states of matter between the liquid state and the crystal state in some materials. They can be characterized by a long-range orientational order of the molecules and, as a consequence,...
There are significant differences in microvasculature density, tortuosity, and anisotropy of cancerous and benign tissue, which makes non-invasive methods to quantify these microvascular architectural properties highly relevant for applications like monitoring the response to anti-angiogenic treatments. We present a method to quantify these properties using ultrasound multiple scattering from contrast...
The feasibility of Shear Wave Elastography (SWE) for assessing fiber organization in anisotropic tissues based on the 3D spatial anisotropy in shear wave (SW) propagation has been demonstrated. In this work, we investigated the performance of SWE in mapping myocardial anisotropy of the left ventricular (LV) wall while increasing the uniaxial stretch. Additionally, a profound study of the occurring...
In most studies on vascular shear wave imaging (SWI), only longitudinal section is mainly concerned, and the radial motion and reflected waves are not considered in cross section. It is important to investigate the SWI in cross section when evaluating the anisotropy of the vessel wall or the complete plaque composition. In our previous study (He et al, UMB 2017), a novel method based on coordinate...
Structure-property relationships in bulk materials can be important in establishing sensing methods to assess the state of material microstructure. This is particularly true for nuclear graphites since these materials can display anisotropy and can become oxidized under service conditions. Both anisotropy and oxidation-induced porosity can influence structural integrity and this must be confirmed...
Tissue mechanical anisotropy has been shown to be diagnostically relevant in numerous clinical applications. Anisotropy can be assessed using acoustic radiation force-based techniques, including Acoustic Radiation Force Impulse (ARFI) and Viscoelastic Response (VisR) ultrasound. In this work, ARFI peak displacement (PD), as well as VisR relative elasticity (RE) and relative viscosity (RV), were implemented...
While skeletal muscle is often assumed to be structurally transversely isotropic (TI), its mechanical anisotropy is not well characterized in vivo. VisR ultrasound, a technique that provides information about the viscoelastic mechanical response of tissue, can be used for such in vivo characterization. Specifically, VisR-derived Relative Elasticity (RE) provides directionally dependent information...
Previous work has shown that the degree of anisotropy in tissue can be assessed using Acoustic Radiation Force Impulse (ARFI) imaging performed with a geometrically asymmetric excitation. In this work, we investigate the clinical relevance of mechanical anisotropy in Duchenne muscular dystrophy (DMD). Anisotropy assessment was performed using relative elasticity (RE) and relative viscosity (RV) parameters...
The kidney is an anisotropic organ, with higher elasticity along versus across nephrons. The degree of elastic anisotropy in kidney may be diagnostically relevant if properly exploited; however, if improperly controlled, anisotropy may confound stiffness measurements. The purpose of this study is to demonstrate a novel method for selectively exploiting or obviating elastic anisotropy in kidney using...
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