Developing methods for imaging the microvasculature using contrast enhanced ultrasound

Contrast agents in medical imaging are specifically designed for each different imaging modality. For ultrasound imaging contrast agents are in the form of gas filled microbubbles. These microbubbles expand and contract when exposed to the ultrasound wave and their echoes can be distinguished from echoes from surrounding tissue. In vivo they pass through blood vessels of a large range of sizes. Abnormalities in the microvasculature, the narrowest blood vessels, are associated with a large range of diseases including cancer and cardiovascular disease. Developing selective imaging of these blood vessels would allow changes or abnormalities in microvasculature to be identified for disease diagnosis and therapy monitoring. In order to achieve this it is important to understand how microbubble response to ultrasound changes when microbubbles are in different size blood vessels. We have developed an experiment to enable such an acoustic investigation. Echoes from microbubbles flowing through m and m diameter tubes have been collected. The frequency content of the echoes and survival of the microbubbles over consecutive echoes has been assessed. Higher frequency echoes and increased microbubble destruction have been found from microbubbles flowing in the narrower tube. These observations highlight physical differences in microbubble behaviour in different diameter tubes and further work is needed for optimal use of this information.