ABSTRACT
Contrast agents are used in all imaging modalities to increase the sensitivity of the imaging technique by altering the image contrast between different structures. Ultrasonic contrast agents are composed of a solution of gas-filled microbubbles. Commercially available ultrasonic contrast agents are microbubbles filled with a gas and surrounded by a thin outer layer or shell. Gas-filled microbubbles scatter ultrasound much more effectively than liquid or solid-filled microbubbles of comparable size and as a result when injected intravenously, increase the magnitude of the ultrasound signal from vascular spaces. Ultrasound contrast microbubbles have a finite lifetime as microbubbles, and as such activation of the agents is recommended just prior to clinical usage. Activation tends to include either mechanical or manual agitation or, be by injection of saline followed by manual agitation. The degree of scattering is maximal if the ultrasonic wave is at the resonant frequency of the microbubbles.
