Response of bubbles to diagnostic ultrasound: a unifying theoretical approach

Abstract

The scattering of ultrasound from bubbles of ∼ 1µm radius, such as used in contrast enhancers for ultrasound diagnostics, is studied. We show that sound scattering and "active" emission of sound from oscillating bubbles are not contradictory, but are just two different aspects derived from the same physics. Treating the bubble as a nonlinear oscillator, we arrive at general formulas for scattering and absorption 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 than 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 sections exceed the scattering cross sections.

Single-bubble sonoluminescence

“…When injected intravenously, the bubbles allow for brighter images and higher contrast. The nonlinearity of bubble dynamics and the violent collapses help to increase the bubble response and imprint a distinctive signature onto the emitted sound, making it easier to distinguish bubble echoes from unwanted tissue reflections (de Jong and Hoff, 1993;Hilgenfeldt, Lohse, and Zomack, 1998;Frinking et al, 1999). Yet even here the potential for various kinds of ''cavitation damage'' has to be carefully assessed: mechanical damage to living tissue (Barnett, 1986), thermal hazard from the absorption of high-frequency sound in tissue and blood (Wu, 1998;Hilgenfeldt et al, 2000), or chemical hazard from the sonochemical production of radicals inside the body (Barnett, 1986).…”

Ultrasound–biophysics mechanisms

“…Even though this section deals with non-thermal mechanisms, UCAs can have an effect on bulk tissue heating (Hilgenfeldt et al, 1998(Hilgenfeldt et al, ,2000Chavrier and Chapelon, 2000;Holt and Roy, 2001;Sokka et al, 2003;Umemura et al, 2005). Typically, there is at least a 2-4 times enhancement of tissue heating by cavitation, or, if the bioeffect were a lesion, the lesion volume was likewise enhanced.…”

Ultrasound contrast agents : dynamics of coated bubbles

“…For small amplitudes of oscillation an oscillating bubble behaves as a harmonic oscillator. The time-dependent radius R can be written as R = R 0 (1 + x (t)) and through a linearization of the Rayleigh-Plesset [29,30] equation around the initial radius R 0 the relative radial excursion is obtained:…”