Abstract
The introduction of ultrasound contrast agents will bring new applications of this diagnostic imaging technology into clinical practice. Vascular, organ-specific, and oral agents are now in clinical trials and will soon be available. The development and properties of ultrasound contrast agents, most of which are based on gas-filled microbubbles, are reviewed. The first group of agents designed to overcome the limitations of free gas bubbles were of more uniform size but were either too large to cross the pulmonary capillary bed or lasted for only a short time in the circulation. The next group was able to produce enhancement over a period of minutes, but did not enhance the parenchyma of organs. The most recently developed intravenous agents exhibit parenchymal enhancement or are tissue-specific during B-mode imaging. Oral contrast agents may be used to reduce the artifacts created by gas in the gastrointestinal tract and to more clearly image the upper abdomen. Specific agents within each of the groups are described. The use of harmonic imaging is reviewed.