Ultrasound Contrast Agents and Imaging of Cerebrovascular Disease

Ultrasound contrast agents (UCA) consist of shell-encapsulated air- or gas-filled microbubbles, which are capable of surviving the heart transit and are able to pass through the lung's capillary bed when injected intravenously. They massively increase the backscattered ultrasound signals, which is clinically useful in all situations of slow and low flow as well as insufficient ultrasound penetration. Because UCA act as intravascular contrast agents, diagnosis of vessel occlusion can be made with high diagnostic confidence based on a lack of contrast enhancement. In the first section of this review, the acoustical properties, the intricate balance of forces, which act on UCA in the human circulation, and UCA-specific ultrasound imaging modes are summarized. In the second section, current clinical applications are summarized and the level of evidence regarding key statements is evaluated using the American Academy of Neurology rating system. The final section is devoted to yet experimental applications, where accumulating data suggest that use of UCA has the potential to be clinically useful and to become incorporated into routine clinical practice.