Ultrasonic characterization of the nonlinear properties of contrast microbubbles

The nonlinear properties of microbubble contrast agents have been used to c reate contrast-specific imaging modalities such as harmonic imaging and sub harmonic imaging. Thus, a better understanding of the nonlinear performance of contrast microbubbles may enhance the diagnostic capabilities of medica l ultrasound (US) imaging. The first and second harmonic, the 1/2 order sub harmonic and the 3/2 order ultraharmonic components in spectra of scattered signals from Optison microbubbles insonified at 2 and 4 MHz have been inve stigated using an in vitro laboratory pulse-echo system. The development of these signal components over time is quite different for 2-MHz insonificat ion compared to 4-MHz insonification. Scattered subharmonic and ultraharmon ic signals are much more time-dependent than first and second harmonic echo es. The dependence of the first and second harmonic, subharmonic and ultrah armonic components on acoustic pressure for 2-MHz insonification is similar to that for 4-MHz insonification, The first and second harmonic components increase linearly with acoustic pressure (in double logarithmic scales) an d the subharmonic and ultraharmonic amplitudes undergo rapid growths in the intermediate acoustic pressure range and much slower increases at both low er and higher acoustic pressures. (C) 2000 World Federation for Ultrasound in Medicine & Biology.