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Ultrasound-Enhancing Agents
Currently Available Second-Generation Ultrasound Contrast Agents
The 2018 American Society of Echocardiography Guidelines recommended changing the terminology of ultrasound contrast agents to ultrasound-enhancing agents (UEAs) for the purpose of distinguishing UEAs from traditional iodinated or magnetic resonance agents. The currently available UEAs in the United States are Optison (General Electric Healthcare), Lumason (Bracco Healthcare), and Definity (Lantheus Imaging). Lumason is the same as what is marketed as Sonovue in 44 other countries, including all of Europe, Brazil, India, and China. Sonozoid (General Electric Healthcare) is approved in Japan and Norway for liver tumor imaging but not for cardiac applications ( Table 18.1 ). Lumason, Optison, and Definity are currently approved only for left ventricular opacification (LVO), but Lumason is also approved for adult and pediatric liver and vesicular imaging. In Europe, SonoVue is approved for improving the detection of coronary artery disease and Doppler enhancement. However, all of these agents have been used to examine myocardial blood flow with perfusion imaging techniques available for almost 20 years on commercially available ultrasound systems. ,
TABLE 18.1
Commercially Available Second-Generation Ultrasound Contrast Agents
| Agent | Manufacturer | Shell | Gas | Approved |
|---|---|---|---|---|
| Optison | GE Healthcare | Albumin A-type protein |
Perfluoropropane | LVO: United States, Europe |
| Definity | Lantheus Medical Imaging | Phospholipid | Perfluoropropane | LVO: United States, Europe |
| SonoVue/Lumason | Bracco Diagnostics | A-type lipid | Sulfur hexafluoride | LVO and Doppler: United States, Europe, Brazil, India, China a |
| Sonozoid a | Ge Healthcare | Lipid | Perfluorobutane | Noncardiac liver tumor imaging: Japan and Norway |
LVO, Left ventricular opacification.
a Highest population countries and continents listed. SonoVue is approved in a total of 44 countries.
Ultrasound Contrast Agent Composition
The improvement in LVO achieved with UCAs after venous injection or infusion has been related to the incorporation of high-molecular-weight gases inside the microbubble shell (see Table 18.1 ). High-molecular-weight gases (sulfur hexafluoride or perfluorocarbons like perfluoropropane) have both lower diffusivity and lower blood solubility, which prolongs their gas phase in blood. Imaging techniques have been modified to image microbubbles at very low mechanical indices (<0.2) using fundamental nonlinear imaging.
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