In Vivo Dispersion Sensing Using Wearable Ultrasound Shear-Wave Elastometry.

We report the first demonstration of wearable ultrasound shear-wave elastometry (wUS-SWEM) for in vivo multifrequency shear-wave (SW) dispersion sensing in human skeletal muscle. SW dispersion measurements characterize tissue viscoelasticity, and wearable ultrasound devices enable stable tissue coupling during body movement, supporting time-resolved mechanical sensing. An SW multifrequency pulse (SW-MFP) spanning 100-300 Hz in 50-Hz increments was generated by the device's mechanical SW actuator and applied to the upper arm of a human subject during mild isometric biceps contraction, while two spatially separated ultrasound transducers (UTs) in the device acquired pulse-echo signals in $M$ -mode over repeated SW-MFP excitations. Depth-, time-, and frequency-resolved SW velocity (SWV) was estimated from inter-UT phase lags of the detected SW displacements at each SW frequency after narrowband separation of the SW-MFP displacement components. We define measurement reliability metrics based on the complex conjugate product (CCP) magnitude and circular phase statistics of the detected SW displacements to identify depth-time-frequency regions supporting reliable phase-lag estimates. Within an identified 10.7-21.9 mm region of interest (ROI) containing reliable estimates across all employed SW frequencies, the estimated SWV in an example subject increased from $5.55{\,}\pm {\,}0.32$ m/s at 100 Hz to $8.98{\,}\pm {\,}0.31$ m/s at 300 Hz, exhibiting the dispersive behavior expected for skeletal muscle in the experimental configuration used here. A similar overall increase in SWV with frequency was observed across five subjects.