1. An ultrasonic diagnostic imaging system comprising: a two dimensional array transducer which transmits beams in different directions in a volumetric region; a beamformer coupled to the two dimensional array transducer; a beamformer controller, coupled to the beamformer, which causes the array transducer to scan two image planes located in different elevation planes with respect to each other; a scan converter, coupled to the beamformer, which produces real time images of the two image planes; and a display, coupled to the scan converter, which displays the two real time images.