Speed of sound and shear wave speed for calf soft tissue composition and nonlinearity assessment

Abstract

Background: The purpose of this study was threefold: (I) to study the correlation of speed-of-sound (SoS) and shear-wave-speed (SWS) ultrasound (US) in the gastrocnemius muscle, (II) to use reproducible tissue compression to characterize tissue nonlinearity effects, and (III) to compare the potential of SoS and SWS for tissue composition assessment.Methods: Twenty gastrocnemius muscles of 10 healthy young subjects (age range, 23-34 years, two females and eight males) were prospectively examined with both clinical SWS (GE Logiq E9, in m/s) and a prototype system that measures SoS (in m/s). A reflector was positioned opposite the US probe as a timing reference for SoS, with the muscle in between. Reproducible tissue compression was applied by reducing probereflector distance in 5 mm steps. The Ogden hyperelastic model and the acoustoelastic theory were used to characterize SoS and SWS variations with tissue compression and extract novel metrics related to tissue nonlinearity. The body fat percentage (BF%) of the subjects was estimated using bioelectrical impedance analysis.Results: A weak negative correlation was observed between SWS and SoS (r =−0.28, P=0.002). SWS showed an increasing trend with increasing tissue compression (P=0.10) while SoS values decayed nonlinearly (P<0.001). The acoustoelastic modeling showed a weak correlation for SWS (r =−0.36, P<0.001) but a very strong correlation for SoS (r =0.86, P<0.001), which was used to extract the SoS acoustoelastic parameter. SWS showed higher variability between both calves [intraclass correlation coefficient (ICC) =0.62, P=0.08] than SoS (ICC =0.91, P<0.001). Correlations with BF% were strong and positive for SWS (r =0.60, P<0.001), moderate and negative for SoS (r =−0.43, P=0.05), and moderate positive for SoS acoustoelastic parameter (r =0.48, P=0.03).Conclusions: SWS and SoS provide independent information about tissue elastic properties. SWS correlated stronger with BF% than SoS, but measurements were less reliable. SoS enabled the extraction of novel metrics related to tissue nonlinearity with potential complementary information.

Measured Hyperelastic Properties of Cervical Tissue with Shear-Wave Elastography

“…This study and many other studies support the theory that pressure on soft tissue changes its shear-wave speed measurement [ 11 , 12 , 13 , 14 , 15 ]. The raw results showed that even when minimal pressure is applied, there are still changes in the measured speed due to the placement of the probe.…”

“…The nonlinear behaviour of tissue causes errors in the measurements made since, in most clinical settings, the pressure from ultrasound probes is unregulated. This phenomenon, known as “tissue stiffening” or “strain stiffening”, is present in most soft tissues, for example, breast tissue [ 11 ], heel pad [ 12 , 13 ], calf muscle [ 14 ] and thyroid gland [ 15 ]. The occurrence of tissue stiffening is especially detrimental for cervical elastography as the probe is in direct contact with the tissue, and the shape of the probe causes non-uniform deformation [ 16 ].…”

Toward Speed-of-Sound Anisotropy Quantification in Muscle With Pulse-Echo Ultrasound

“…However, shear and longitudinal waves interrogate fundamentally different mechanical tissue properties [28]. Their propagation velocities differ by three orders of magnitude, resulting in decoupled relationships between the two velocities and elastic moduli [31]. Hence, our work not only complements other studies on the topic but is pivotal to characterize mechanical tissue properties comprehensively.…”

“…Such a medium is characterized by five independent elastic parameters, describing, for instance, the longitudinal-and shear-wave velocities along and across the symmetry axis. In soft tissue, however, shear-wave velocities are negligible in comparison to longitudinal-wave velocities [31]. Therefore, it is possible to describe muscle properties using only three independent parameters.…”

“…1(b)], with the probe-reflector distance L controlled by a positioning frame and a distance sensor [4]. This setup has already been applied in various clinical studies for the assessment of breast [34], [35] and muscle tissue [12], [13], [31], [36]. The reflector allows us to measure first-arrival reflection traveltimes t SR of waves propagating from a source at x S to a receiver at x R .…”