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 and tissue attenuation affects ultrasound focusing for creating shear waves, the resulting phase screen, acoustic field, shear wave amplitude and the shear wave velocity were measured. A Verasonics ultrasound system equipped with a linear array transducer (L7-4), an excised piece of swine belly tissue consisted of the skin, subcutaneous fat, and muscle and an elastic phantom were used. The ultrasound frequency used to generate shear waves was varied. The acoustic pressure and shear wave amplitude decreased with the introduction of the tissue layers. Decreasing the ultrasound frequency was important for maintaining a focused beam for creation of shear waves in the presence of phase aberration and attenuation. Analysis of shear wave production with a tissue layer (aberration and attenuation case) and measured phase screen (only aberration case) showed that tissue attenuation affects the shear wave generation more than tissue aberration.