Optimization of microbubble destruction

The rapid destruction of an ultrasound contrast agent on the time scale of microseconds which occurs when the bubble fragments provides the opportunity to distinguish echoes from bubbles and tissue. Fragmentation occurs when non-spherical oscillations in the bubble become large enough to produce a pinch-off of bubble fragments. The authors find that two factors are important in gauging the probability of fragmentation, the ratio of maximum expansion diameter to minimum compression diameter and the peak wall velocity. For wideband insonation (1-2 cycle insonation), the maximum expansion of a bubble relative to the initial diameter and the occurrence of fragmentation increase with decreasing bubble initial diameter. The ratio of expansion and the occurrence of fragmentation also increase with decreasing center frequency of for all frequencies and initial an increase in transmitted peak negative pressure yields increased expansion ratio and occurrence of fragmentation. A dependence of fragmentation on the phase of insonation is observed. A transmitted pulse of 0° phase (compression precedes rarefaction) produces fragmentation less than the same pulse but of phase 180° (rarefaction precedes compression). The maximum expansion of the bubble is larger in the 0° case but the wall velocity is larger in the 180° case