Ultrasound contrast
Ultrasound images can be improved by using a contrast agent, although these are entirely different from those used for X-ray contrast media. (Foetal examinations, though, do not employ contrast agents.) With X-rays, the contrast agent's ability to absorb these rays is the determining factor in giving good discrimination. An ultrasound contrast agent's task is to increase the refraction and reflection of the ultrasonic waves.
One way of doing this is to use a contrast agent which consists of millions of tiny air bubbles. Each of the air bubbles will reflect the sound wave. In this new and rapidly developing field, tiny gas bubbles with a size of less than 10 µm are stabilised within a biodegradable shell. Without this shell, the bubbles would be stable only transitorily (for a matter of perhaps some seconds), as the unstabilised bubbles would soon merge into larger bubbles. Besides being potentially hazardous to the patient, large bubbles have different, and less suitable, reflective properties. By filling the blood stream with the ultrasound contrast agent, it is possible, for example, to increase significantly the reflections from the blood-filled chambers of the heart, so that their image on the monitor will be clearly differentiated from those of the heart muscle itself.
GE Healthcare Glossary