Detection procedures of ultrasound contrast agents

In the early days, it was believed that ultrasound contrast agents (UCA) could be sufficiently detected and imaged with the conventional imaging methods nowadays referred to as fundamental imaging. Newer imaging techniques proved to be more sensitive and are based on specific properties of the UCA. In general, these new characteristics involve non-linear and transient characteristics of contrast agents that appear at the high end of the diagnostic acoustic intensity. Imaging modalities used today for UCA are, besides fundamental imaging, second harmonic imaging, power Doppler, harmonic power Doppler, pulse inversion and pulse inversion Doppler, multi-pulse imaging and subharmonic imaging. Although the results of conventional second harmonic imaging are still not optimal for perfusion imaging applications, in combination with Doppler techniques (colour Doppler, power Doppler) it is one of the most sensitive techniques currently available in terms of agent-to-tissue ratio. Further improvements in current and future detection methods demand a complete understanding of the ultrasound-UCA interaction.