Shear wave elastography in ex vivo and in vivo skin using high-frequency ultrasound imaging

Real-time, high-resolution imaging of the skin, including epidermal and dermal structures, is now possible using high-frequency ultrasound scanning systems. Potential extensions include shear-wave elastography. In this study, feasibility for characterization of skin layer elasticity using high-frequency ultrasonic imaging is demonstrated using a 50 MHz linear array and a small-animal ultrasound scanner (Vevo 2100, MS700 array). High-frequency time-harmonic shear wavefields (2-5kHz) are generated in the skin using a mechanical shaker. Wavefields are mapped by processing pulse-echo image sequences recorded at relatively low frame rates (513 fps), accounting for effects of signal aliasing and timing of multiple scan lines. Shear wavespeeds are then measured in ex vivo porcine skin and in vivo human forearm skin using spatial Fourier analysis, linear regression of measured wavefield phase maps, and algebraic inversion of wavefields using a finite difference method. Results demonstrate consistent measurements of shear wavespeed in the skin.