A system and method for fundamental real-time imaging of the non-linear response of tissue perfused with a contrast agent are disclosed. An image with increased sensitivity to non-linear responses can be achieved by detecting the ultrasound response at the fundamental frequency from tissue perfused with a contrast agent and excited by multiple excitation levels. The responses detected from the multiple excitation levels may be gain corrected in an amount corresponding to the difference in magnitude of the excitation levels, then mathematically combined. The mathematical manipulation serves to remove linear responses to the fumdamental excitation from the detected image. An ultrasonic contrast agent and tissue imaging system can be implemented with a transducer, first and second transmitters, a receiver, a control system, a processing system and a display. The transmitters generate electrical signals that are translated by the transducer into first and second pressure waves respectively, the respective pressure waves being of different power magnitudes. A control system electrically coupled to the transmitters, the transducer, and a receiver, coordinates pressure wave transmissions and the reception of ultrasonic responses. A processing system removes linear responses leaving the non-linear responses from the contrast agent and the surrounding tissue. Lastly, a display configured to receive the non-linear response creates an image of the insonified contrast agent and surrounding tissue.