Pa. Dayton et al., A PRELIMINARY EVALUATION OF THE EFFECTS OF PRIMARY AND SECONDARY RADIATION FORCES ON ACOUSTIC CONTRAST AGENTS, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 44(6), 1997, pp. 1264-1277
Primary and secondary radiation forces result from pressure gradients
in the incident and scattered ultrasonic fields, These forces and thei
r dependence on experimental parameters are described, and the theory
for primary radiation force is extended to consider a pulsed traveling
wave, Both primary and secondary radiation forces are shown to have a
significant effect on the flow of microbubbles through a small vessel
during insonation. The primary radiation force produces displacement
of microspheres across a 100 micron vessel radius for a small transmit
ted acoustic pressure, The displacement produced by primary radiation
force is shown to display the expected linear dependence on the pulse
repetition frequency and a nonlinear dependence on transmitted pressur
e, The secondary radiation force produces a reversible attraction and
aggregation of microspheres with a significant attraction over a dista
nce of approximately 100 microns, The magnitude of the secondary radia
tion force is proportional to the inverse of the squared separation di
stance, and thus two aggregates accelerate as they approach one anothe
r, We show that this force is sufficient to produce aggregates that re
main intact For a physiologically appropriate shear rate, Brief interr
uption of acoustic transmission allows an immediate disruption of the
aggregate.