Ultrasound imaging is a commonly used medical diagnostic technique where ultrasound is inserted in the body and where the sound that is reflected at dense body structures ('the echo') is detected and visualized on a monitor screen. A gynecologist uses ultrasound imaging to screen a fetus in the uterus. A cardiologist uses ultrasound imaging, termed echocardiography, to visualize the movement of the heart wall and the heart valves.

A cardiologist is also interested in the flow field of the blood in the heart chambers and in the perfusion of the heart muscle. However, blood is a poor ultrasound scatterer and in these cases a cardiologist will use a contrast agent to increase the reflection of ultrasound by the blood pool.