Contrast echocardiography: Contrast agents, safety, and imaging technique
- Neil J Weissman, MD
Neil J Weissman, MD
- Professor of Medicine
- Georgetown University School of Medicine
Contrast echocardiography is a technique for improving echocardiographic resolution and providing real time assessment of intracardiac blood flow. Agitated saline contrast provides contrast in the right heart and enables detection of right to left shunts. Opacification of the left ventricular (LV) cavity by contrast agents developed to traverse the pulmonary vasculature permits improved endocardial border detection . Contrast echocardiography can also enhance delineation of Doppler signal . Additional uses of contrast echocardiography are to assess myocardial perfusion  and viability .
The development and safety of microbubbles for echocardiographic contrast and the optimization of the echocardiographic settings for visualizing contrast will be reviewed here. The current and potential clinical applications of CE are discussed separately. (See "Contrast echocardiography: Clinical applications".)
MICROBUBBLE CONTRAST AGENTS
Mechanism of contrast — As sound travels from one medium to another, the change in density (known as acoustic impedance) at the interface causes the reflection of sound waves . The greater the difference in the media densities, the more echogenic the interface. Gas is an excellent contrast agent since it is 100,000 times less dense than blood.
Agitated saline contrast — Agitated saline solution administered via intravenous injection provides air microbubble contrast in the right heart. The air microbubbles are short-lived and diffuse into the lungs when traversing the pulmonary circulation. Therefore the microbubbles enter the left heart only in the presence of a right to left intracardiac or extracardiac (pulmonary arteriovenous) shunt. Saline microbubbles are therefore helpful in examining the right heart and identifying shunts. (See "Contrast echocardiography: Clinical applications", section on 'Clinical applications for agitated saline contrast' and "Patent foramen ovale", section on 'Ultrasound techniques'.)
Transpulmonary passage of contrast agents — To allow left heart evaluation, an ideal contrast microbubble must be small and durable enough to traverse the pulmonary circulation to pass into the left heart from an intravenous injection. Improvements in contrast agents have resulted from the exploitation of knowledge concerning both the mechanisms of echogenicity and the impediments to transpulmonary passage.
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- MICROBUBBLE CONTRAST AGENTS
- Mechanism of contrast
- Agitated saline contrast
- Transpulmonary passage of contrast agents
- - Second generation contrast agents
- Agitated saline safety
- Second generation contrast safety
- OPTIMAL ECHOCARDIOGRAPHIC SETTINGS
- Harmonic detection
- Intermittent or transient imaging
- Low mechanical index imaging
- Gray discrimination
- Mode of contrast injection
- SUMMARY AND RECOMMENDATIONS