Experimental Investigation of Guided Wave Imaging in Thin Soft Media under Various Coupling Conditions

Abstract

Guided wave imaging for the artery remains in its infancy in clinical practice mainly because of complex arterial microstructure, hemodynamics and boundary conditions. Despite the theoretically known potential effect of the surrounding medium on guided wave propagation in thin media in non-destructive testing, experimental evidence pertaining to thin soft materials, such as the artery, is relatively scarce in the relevant literature. Therefore, this study first evaluated the propagating guided wave generated by acoustic radiation force in polyvinyl alcohol-based hydrogel plates differing in thickness and stiffness under various material coupling conditions (water and polyvinyl alcohol bulk). A thin-walled polyvinyl alcohol hollow cylindrical phantom coupled by softer gelatin–agar phantoms and an excised porcine aorta surrounded by water and pork belly were further examined. Guided waves in the thin structure and shear waves in the bulk media were captured by ultrafast ultrasound imaging, and guided wave dispersion as a function of the frequency–thickness product was analyzed using the zero-order anti-symmetric Lamb wave model to estimate the shear modulus of each thin medium studied. Results confirmed the deviated shear modulus estimates from the ground truth for thin plates, the thin-walled hollow cylindrical phantom and the porcine aorta bounded by stiffness-unmatched bulk medium. The findings indicated the need for (i) careful interpretation of estimated shear moduli of thin structure bounded by bulk media and (ii) a generalized guided wave model that takes into account the effect of coupling medium.