スタント カワン, 陳 民, 奥島 基良

Kawan SOETANTO, Man CHAN, Motoyoshi OKUJIMA

桐蔭大学横浜大学工学部桐蔭人間科学工学センター

Toin Human Science and Technology Center Toin University of Yokohama

キーワード : Annihilation mechanism , Longevity of microbubbles , Surfactants, Ultrasound contrast agent

Microbubbles are usually used as an ultrasound contrast agent because of their excellent scattering properties. However their short longevity in vitro and in vivo make their application in clinical trials very difficult. We suggest that to extend their longevity, a coating layer is necessary, and, accordingly, we used surfactants to form the coating layer of microbubbles in this study of the annihilation mechanisms of surfactant-coated microbubbles in saline water. The experimental results suggest that two kinds of mechanisms may account for surfactant annihilation of microbubbles: (1) dissolution of gas from microbubbles into the surrounding solution, and (2) dissolution of the coating layer into the sourrounding solution. Both simulated and experimental results have shown that dissolution of gas from microbubbles into the surrounding solution is very important. This phenomenon is demonstrated by decrease in size of microbubbles over time. Decrease in surface tension of the liquid is known to greatly decrease the shrink rate of microbubbles coated with surfactants. Experimental results show that percentage decrease in number of microbubbles over time is much greater than the corresponding percentage decrease in their size. Thus the dissolution of coating material was also thought to be very important in determining the decrease in number of microbubbles. We further propose that the rate of decrease in number of microbubbles produced by different surfactants is related to the dissolution rate of the surfactant. Furthermore, number of microbubbles that can be produced from a surfactant is known to depend on both the particular surfactant used and its concentration. Change in number and size of surfactant microbubbles over time does not depend on concentration of the surfactant solution from which the microbubbles are produced.