Instituto de Física, Universidade Federal de Alagoas, Maceió, AL 57072-970, Brazil.
Phys Med Biol. 2011 Sep 21;56(18):5985-93. doi: 10.1088/0031-9155/56/18/013. Epub 2011 Aug 22.
Vibro-acoustography (VA) is a medical imaging method based on the nonlinear interaction of two or more distinct ultrasound beams whose frequencies differ by several kHz. In turn, the interacting waves produce a difference-frequency signal which carries the information of the imaged tissue region. Two mechanisms are responsible for the difference-frequency generation (DFG) in VA, namely the dynamic (oscillatory) radiation force and the scattering of sound-by-sound. The role and importance of each phenomenon in VA is assessed here. A theoretical model based on Westervelt's equation for the DFG in the nonlinear scattering of two incident ultrasound waves by a small rigid sphere (compared to the incident wavelengths) is presented. Furthermore, a scattering experiment using VA is devised and the data show very good agreement with the proposed theory. The results reveal that the effect of scattering of sound-by-sound is the dominant component in the DFG in VA rather than the dynamic radiation force.
声振造影（VA）是一种基于两个或多个不同频率相差数 kHz 的超声束的非线性相互作用的医学成像方法。反过来，相互作用的波会产生一个差频信号，它携带被成像组织区域的信息。VA 中的差频产生（DFG）有两种机制，即动态（振荡）辐射力和声散射。这里评估了每种现象在 VA 中的作用和重要性。提出了一种基于 Westervelt 方程的理论模型，用于在小刚性球（与入射波长相比）对两个入射超声的非线性散射中的 DFG。此外，还设计了一个使用 VA 的散射实验，数据与提出的理论吻合得非常好。结果表明，声散射的影响是 VA 中 DFG 的主要组成部分，而不是动态辐射力。
