Fig. 2.

Spatial distribution of a representative acoustic radiation force excitation intensity field, as simulated in 3D using Field II, shown in a quarter-symmetry volume as isosurfaces of relative intensity that peak in red at the focus. The yellow arrows show relative direction of the Poynting vector associated with the propagating acoustic waves generating this acoustic radiation force excitation. While the near-field of the excitation distribution has some lateral component to the force, the impact of this lateral force is minimal at the focal depth, and the symmetrically opposing lateral displacements related to these minor lateral forces in the near field cancel one another out along the axis of symmetry of the excitation. For these reasons, the acoustic radiation force vectors are applied in a purely axial orientation in these simulations.