Theoretical model for the threshold onset of contrast microbubble oscillations

It has been reported recently through high speed optical observations of phospholipid-coated contrast microbubbles that there is a threshold value for the acoustic pressure amplitude below which the radial oscillation of the microbubbles does not occur. This paper suggests that the observed threshold behavior is a consequence of the fact that a phospholipid layer has a certain value of the limiting shear stress so that its deformation does not start until this limiting value is exceeded. A theoretical model is proposed for the description of this phenomenon. The model explains the experimentally observed dependence of the threshold onset of microbubble oscillation on the resting bubble radius.