Effects of phase aberration on acoustic radiation force-based shear wave generation

Tissue elasticity is measured by shear wave elasticity imaging methods using acoustic radiation force to create the shear waves. Reliable tissue elasticity measurements are achieved with strong shear waves. Phase aberration and tissue attenuation can hamper the generation of shear waves for in vivo applications. In this study we explored how phase aberration affects ultrasound focusing for creating shear waves and evaluate the resulting shear wave amplitude and the shear wave velocity. A Verasonics ultrasound system equipped with a linear, a curved linear, and a phased array transducer (L7-4, C4-2 and P4-2) was used. An excised piece of swine belly tissue consisted of the skin, subcutaneous fat, and muscle were placed on top of the elastic phantom to evaluate the shear wave produced when transmitting through the different layers. The ultrasound frequency used for three transducers was varied to evaluate the resulting shear waves with the different tissue layers. Analysis of shear wave production with real tissue layers showed that large fat layers and combinations of skin, fat, and muscle defocused the ultrasound beam most, thereby decreasing the shear wave amplitudes.