ACOUSTIC PROPERTIES OF SURFACTANT MICROBUBBLES IN RELATION TO THEIR LIFETIME IN-VITRO AS DETERMINED BY DIFFUSION

In this study, to make microbubbles less than 10 mu m and to extend th eir lifetime, sodium laurate is chosen as the material for the coating of microbubbles. In studies of ultrasound contrast agents, the author s are the first to report on the use of sodium laurate as the material for manufacturing the microbubble contrast agent. In addition, the me thod of producing microbubbles using a syringe is proposed. Using sodi um laurate and the syringe method, microbubbles with diameter less tha n 10 mu m are produced. From the result of simulation, it is found tha t the dissolved gas concentration in the solution surrounding microbub bles plays an important role in determining microbubble lifetime. Micr obubbles without coating are calculated to have a lifetime of less tha n 1 min when the dissolved concentration of gas is about 90%. On the o ther hand, the lifetime of microbubbles made from sodium laurate is ab out 5 min longer than the calculated lifetime. Therefore, it is hypoth esized that when the dissolved gas in the solution is above a certain level, the mechanism governing annihilation of microbubbles is the dis solution of the surfactant coating layer into the solution, instead of the diffusion of gas from the microbubbles. Since the dissolution tim e of surfactants is longer than the dissolution time of gas, the lifet ime becomes longer.