3D simulations of difference frequency effects on a blood vessel in ultrasound-stimulated vibro-acoustography

Ultrasound-stimulated vibro-acoustography (USVA) is one of the recent noninvasive techniques that have been developed to explore mechanical properties of soft tissues. USVA is based on the interference of two focused ultrasound beams that have a slightly different frequency. This interference produces time variation to the acoustic radiation force that vibrates the joint focal region at the difference frequency. In this paper, we have simulated displacement amplitudes in the blood vessel using different difference frequencies and elasticity parameters. The difference frequency was varied between 300 Hz and 2.5 kHz, and two different stiffness parameters (60 kPa and 120 kPa) for the blood vessel wall were used. The stimulation transducer used in the simulations consists of two concentric and focused ring elements whose base frequency is 0.75 MHz. The stimulation fields have been computed in a homogeneous domain using the Rayleigh integral. The simulations of the vibrations have been computed using the finite element method. The displacement simulations are computed in an inhomogeneous domain that consists of soft tissue and a blood vessel. From the simulations, it can be seen that USVA is sensitive to the mechanical properties of vessel wall and that the displacements are highly dependent on the difference frequency and the material parameters.