Phase aberration effects on beam shape evaluated with particle motion in an elastic phantom

The phase aberration phenomenon reduces spatial resolution and image contrast of the shear wave-based elasticity images impeding the study and determination of tissue mechanical properties. Shear waves can be used to make measurements of tissue elasticity. These shear waves can be produced by focused ultrasound “push” beams that generate acoustic radiation force and displace the tissue. We investigated the effects of phase aberration on the push beam shape evaluated with particle motion. A Verasonics ultrasound system equipped with a linear array transducer operating at different center frequencies (f₀) was used to perform these experiments. Porcine belly skin, subcutaneous fat, and muscle were separated and placed on top of the elastic phantom. A beam of 300 μs duration focused at a depth of 40 mm from the transducer produced particle motion in the direction of the beam. The beam shape without the tissue layers was determined using a thresholding operation to create a mask from which the particle velocity for each pixel was estimated and used for further calculations. The median particle velocity decreased as various layers were added on the top of the elastic phantom. Moreover, changes in f₀ also affected the particle velocity amplitude.