Microbubbles persistence

Recent experimental studies have confirmed that microbubble persistence is controlled primarily by the dissolution of bubbles and not by removal by the RES. Although the qualitative trends are in agreement with theoretical models, there are some quantitative differences. 

Experiments to distinguish between these two possibilities have often involved measurements of ultrasonic attenuation (ref. 5,9,31,32). The popularity of this approach derives in part from the fact that small impurities in liquids, such as suspended particles, have negligible influence on attenuation in comparison with even a very small concentration of microbubbles (ref. 9). (Microbubbles, in contrast to solid particles, appreciably increase the compressibility of a liquid, introducing forms of viscous losses and nonreversible energy exchanges that do not exist in the case of solid particles.) It is therefore of considerable interest that all fresh tap water samples measured by Turner (ref. 9) showed substantial and persistent abnormal (ultrasonic) attenuation, amounting to a minimum of 44% over that of distilled water it was concluded that this result stemmed from the presence of stabilized micron-sized bubbles. 

In an additional experiment designed to test the persistence of film-stabilized microbubbles as a function of time, a population of stabilized microbubbles generated by Johnson and Cooke was... 

Gas microbubbles are by far the most effective scatterers to use in an ultrasound contrast agent, due to their large differences in acoustic impedance compared with the surrounding blood. However, free bubbles smaller than 7 pm can only persist intact for a few seconds in the blood. This is much less than the required time to reach the target organ from the site of injection. In order for the agent to achieve sufficiently long persistence, gas bubbles have to be stabilized with an outer shell. 

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