Specific characteristics of ultrasound contrast agents

Abstract

Ultrasound contrast agents possess acoustical characteristics which differ from the surrounding medium. Specific signatures of the agent, consisting of free or encapsulated gas bubbles, will improve the discrimination between the blood containing the agent and the tissue. One of the specific signatures is the initiation of a volume pulsation when the ultrasound wave hits a free or encapsulated gas bubble. Depending on the magnitude of the ultrasound wave the pulsation will be linear to the applied pressure or nonlinear to the applied pressure. Nonlinear vibration can be split into stationary (harmonic) and transient (power) scattering. Besides the nonlinear vibration (harmonics), specific characteristics include enhanced scattering as a function of the acoustic amplitude, transient scattering which is very useful for measuring flow, LOC (loss of correlation) imaging, and the persistence as a function of ambient parameters like pressure and temperature. Recently, a 2-D echomachine has been adapted for imaging of the nonlinear vibration of contrast agents and further developments in both hardware and software will be advantageous for the many specific characteristics of these agents.