An ultrasound imaging system that includes a transducer dynamically controls a shear wave front used to image viscoelasticity in a biological tissue. The system receives an indication of a region of interest and selects a shear wave front shape. The system also selects, based on the selected shear wave front shape, focus locations for a plurality of push pulses and a sequence for moving a shear wave source (S1,S2, ...,S6) among the focus locations. The system transmits a series of push pulses according to the selected sequence, and determines a speed of the shear wave front as it passes through the region of interest. Changes in the speed of the shear wave front are related to changes in stiffness within the tissue.
