title: Difference-frequency generation in vibro-acoustography.
abstract: 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.
authors.affiliation: Instituto de Física, Universidade Federal de Alagoas, Maceió, AL 57072-970, Brazil. glauber@pq.cnpq.br
authors.forename: Glauber T
authors.initials: GT
authors.lastname: Silva
authors.forename: Farid G
authors.initials: FG
authors.lastname: Mitri
mesh_terms: D000162:Acoustics; D000818:Animals; D054459:Elasticity Imaging Techniques / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation / Q000379:methods*; D008962:Models, Theoretical; D017711:Nonlinear Dynamics; D012542:Scattering, Radiation; D014465:Ultrasonics