Contrast-enhanced ultrasound achieves new breakthroughs

Evaluations under way at Thomas Jefferson University are focusing on the use of gas-encapsulated microbubble contrast agents with nonlinear ultrasound imaging techniques to not only detect but also help characterize breast cancer noninvasively. Other recent studies have examined how microbubble contrast agents interact with ultrasound acoustic fields to demonstrate the effectiveness of contrast-specific imaging in visualizing microvascular details. This information is useful for the early detection of cancer-related malignancies and lesions and for monitoring tumor angiogenesis. Additionally, research is ongoing to further expand the use of microbubble contrast agents in ultrasound imaging for advanced cardiac applications such as noninvasive pressure estimation for assessing heart and vascular diseases. Diagnostic ultrasound is the most frequently used imaging modality in the world, accounting for approximately 25% of all imaging studies. It offers many potential advantages for noninvasive cancer detection. Ultrasound provides physicians with real-time imaging of tissue structures and their movements. It enables functional imaging of flow in larger blood vessels and organs with higher temporal resolution than MR or CT. Diagnostic ultrasound is generally safe, without harmful ionizing radiation that can potentially raise the risk of cancer, and it has a larger installed equipment base than any other modality. For more than 35 years, researchers have recognized the effectiveness and increased diagnostic capabilities of ultrasound imaging with the use of contrast agents, which improve sensitivity and specificity. With the development of microbubble contrast agents, ultrasound has achieved noteworthy diagnostic breakthroughs and enabled new clinical applications for contrast-enhanced imaging. Ultrasound contrast agents are gas-encapsulated microbubbles less than 8 micron in diameter (about the same size as red blood cells). They are injected intravenously to circulate in the blood stream and improve image quality by increasing the backscattered ultrasound signals from the vasculature of tissue structures.1 Because microbubble contrast agents behave nonlinearly and are acoustically different from surrounding fluids and tissue, the ultrasound signal-to-noise ratio is dramatically increased, resulting in better visualization of blood vessels and organs throughout the body. The nonlinear properties of microbubble contrast agents have been used to create contrast-specific imaging modalities such as harmonic and subharmonic ultrasound imaging. Another novel contrast imaging technique is Micro Flow Imaging (Toshiba America Medical Systems), which combines specific nonlinear properties of the microbubbles with the movement of individual bubbles through tumor neovessels. Micro Flow Imaging allows tracing of individual microbubble contrast agents over time to deliver contrast harmonic images at high resolution with detailed definition. It uses subtraction and summation techniques to outline tortuous vessels that have only minute traces of contrast, producing images captured with maximum intensity. Summed images constructed over time outline even capillary vessels. Examinations using this technique have proved especially useful in assessing the slowly perfused mammary organ, small organ parts, and the microvasculature of abdominal organs.