Rapid synthetic focus ultrasonic imaging with large linear arrays

An ultrasonic diagnostic imaging system and method translates an aperture across an array transducer which is less that the size of the array. At each aperture location a transmit beam is focused above, or alternatively below, the array and a region of interest being scanned from the aperture location, resulting in broad insonification of the region of interest. At the lateral ends of the array the aperture is no longer translated but the focal point of the transmit beam is translated from the same aperture position, preferably with tilting of the beam direction. Multiple receive beams are processed in response to each transmit event and the overlapping receive beams and echo locations are spatially combined to produce synthetic transmit focusing over the center of the image field and noise reduction by spatial compounding at the lateral ends of the image field.