RESPONSE OF BUBBLES TO DIAGNOSTIC ULTRASOUND - A UNIFYING THEORETICALAPPROACH

The scattering of ultrasound from bubbles of similar to 1 mu m radius, such as used in contrast enhancers for ultrasound diagnostics, is stu died. We show that sound scattering and ''active'' emission of sound f rom oscillating bubbles are not contradictory, but are just two differ ent aspects derived from the same physics. Treating the bubble as a no nlinear oscillator, we arrive at general formulas for scattering and a bsorption cross-sections. We show that several well-known formulas are recovered in the linear limit of this ansatz. In the case of strongly nonlinear oscillations, however, the cross-sections can be larger tha n those for linear response by several orders of magnitude. The major part of the incident sound energy is then converted into emitted sound , unlike what happens in the linear case, where the absorption cross-s ections exceed the scattering cross-sections.