Acoustic radiation force impulse (ARFI) scanning uses a swept focus in transmit. Using a changing delay or phase profile across the array during the generation of the ARFI pulse, a time varying focus is provided for the ARFI beam. This time varying focus may be used to extend the focus in depth, azimuth, and/or elevation. Less repetition may be needed to measure tissue characteristics from displacements due to the multi or continuous change in foci within a given ARFI transmit beam.
