Shear wave elastography reveals dispersion regimes in porous materials

Ultrasound shear wave elastography is a well established tool for characterization of biologic tissues. While it has found application in various medical disciplines such as oncology and urology its feasibility for pneumology still has to be shown. We provide experimental results of ultrasound shear wave elastography of porous materials in phantoms and ex-vivo lung tissue. Phantom foams immersed in water show a strong phase velocity dispersion with increasing frequency. Two regimes can be identified in the dispersion curves in the investigated frequency range from 50 to 700 Hz. These experimental results are in reasonable agreement with the theory of porous materials. The results from water-filled phantom foams are compared to gelatin-filled phantom foams. Finally, the phantom study is compared to surface waves dispersion curves of porcine lungs obtained with an ultra-fast optical camera and the first results of ex-vivo shear wave elastography in porcine lung. Ultrasound shear wave elastography is standard in non-porous organs such as muscle, liver, and breast tissue. Its application to porous materials could offer a noninvasive and nonionizing alternative for lung characterization.