Full Characterization of in vivo Muscle as an Elastic, Incompressible, Transversely Isotropic Material Using Ultrasonic Rotational 3D Shear Wave Elasticity Imaging

Abstract

Using a 3D rotational shear wave elasticity imaging (SWEI) setup, 3D shear wave data were acquired in the vastus lateralis of a healthy volunteer. The innate tilt between the transducer face and the muscle fibers results in the excitation of multiple shear wave modes, allowing for more complete characterization of muscle as an elastic, incompressible, transversely isotropic (ITI) material. The ability to measure both the shear vertical (SV) and shear horizontal (SH) wave speed allows for measurement of three independent parameters needed for full ITI material characterization: the longitudinal shear modulus µ L , the transverse shear modulus µ T , and the tensile anisotropy χ E . Herein we develop and validate methodology to estimate these parameters and measure them in vivo, with µ L = 5.77 ± 1.00 kPa, µ T = 1.93 ± 0.41 kPa (giving shear anisotropy χµ = 2.11 ± 0.92), and χ E = 4.67 ± 1.40 in a relaxed vastus lateralis muscle. We also demonstrate that 3D SWEI can be used to more accurately characterize muscle mechanical properties as compared to 2D SWEI.

Anisotropy in ultrasound shear wave elastography: An add-on to muscles characterization

“…However, in pennate muscle shear wave velocity measurements must be supplemented with Bmode acquisition in order to retrieve fiber orientation. Here 3D rotation is definitively needed as demonstrated by Knight et al, 2021 . However, probe rotation is a major drawback and is not applicable to a muscle with constantly changing contraction levels.…”

“…However, in pennate muscle shear wave velocity measurements must be supplemented with Bmode acquisition in order to retrieve fiber orientation. Here 3D rotation is definitively needed as demonstrated by Knight et al, 2021. However, probe rotation is a major drawback and is not applicable to a muscle with constantly changing contraction levels. 3D elastography appears to bridge the gap between these limitations and what is expected from clinicians but still requires expensive device that are rarely if ever available in a clinical setting.…”

“…This method is able to provide the three parameters that characterize an incompressible and TI material: the longitudinal µ // and transverse µ ⊥ shear modulus, and the tensile anisotropy χ E (the ratio between the Young’s modulus parallel and the Young’s modulus perpendicular to the fibers) following an ARFI-SWS. Taking advantage of this modeling method, ultrasonic rotational 3D elasticity imaging was developed to fully characterize muscle mechanical properties ( Knight et al, 2021 ). To estimate the three mentioned parameters, both SH and SV are measured by rotating the probe in 3D.…”

SweiNet: Deep Learning Based Uncertainty Quantification for Ultrasound Shear Wave Elasticity Imaging

“…SWS probability distributions can also be used for maximum likelihood estimation of derived parameters. For example, consider SWS data of skeletal muscle measured at various rotation angles relative to the muscle fibers and the process of fitting an ellipse to these data [47]. Rather than optimizing for the smallest mean error, we could find a curve with the maximum joint likelihood of all SWS data points, using SweiNet's output as the probability function.…”

Quantification of in vivo muscle elastic anisotropy factor by steered push beams

“…However, in transverse isotropic (TI) tissues such as skeletal muscle, two shear moduli µ// and µ⊥ can be defined parallel or perpendicularly to the fibers respectively. Theoretically, also two SW modes can be defined [1,2]: a shear horizontal (SH) and a shear vertical (SV) wave mode. In this case, SW propagation direction and polarization are not either parallel or perpendicular to the tissue symmetry axis, so the SWV is not directly related to a single μ.…”