A medical ultrasonic imaging system transmits a set of two or more substantially identical transmit pulses into a tissue containing a contrast agent. The associated received pulses are filtered with a broadband filter that passes both the fundamental and at least one harmonic component of the echoes. The filtered received pulses are then applied to a clutter filter that suppresses harmonic and fundamental responses from slowly moving and stationary tissue, while clearly showing contrast agent response due to the loss of correlation effect. The disclosed system includes other signal paths for generating conventional B-mode images as well as combined images that include both components from the contrast-specific image as well as components from the B-mode image. An improved user interface allows the user to switch among these three images. Preferably the transmitter generates transmitted pulses having two or more spatially distinct focus zones, thereby improving the uniformity of contrast agent imaging over the imaged region.