Acoustic Nonlinear Behaviour of Microbubble Contrast Agent

We have investigated the nonlinear characteristics of a microbubble contrast agent Sonazoid^R (Nycomed, Norway), including the second, third, 1/2-order, 3/2-order and 5/2-order harmonics. We have measured the 1/2-order subharmonic response to different transmit sound pressure. It is found that subharmonic signals can not be generated until the acoustic pressure reached a certain value, which is the most difference subharmonic from high harmonics. This result is favorable for the further study of the subharmonic in the bubbly liquid. The 3/2-order ultraharmoic response to acoustic pressure was also measured.