Effects of motion on a synthetic aperture beamformer for real-time 3D ultrasound

A synthetic aperture (SA) beamformer is theoretically capable of collecting volume data sets in real-time. Since SA imaging requires phase coherence over multiple transmit events, relative motion between the transducer and target is a concern, especially for a cardiac imaging system. The sensitivity to motion of a sparse transmit SA beamformer was evaluated by simulating a sector scan of a moving point target. The results were quantified by plotting the maximum value of the beamformed signal as function of scan angle. Simulations were used to examine motion in both the axial and lateral directions. Lateral motion, for the speeds simulated (/spl les/2 m/s), did not significantly change the secondary lobes in the radiation patterns. Motion in the axial direction produced more distortion of the radiation pattern; however, the secondary lobes for targets moving at speeds representative of cardiac motion (<80 mm/s) were not significantly different than those for stationary targets. For larger speeds (400-800 mm/s) the secondary lobes rose about 4 dB. These findings were verified experimentally using a 2.6 MHz array. The results indicate that SA beamforming with a sparse transmit array may be feasible for cardiac imaging.