STUDY ON CONTRAST EFFECT OF MICROBUBBLES AS ULTRASOUND CONTRAST AGENTS

In this study, the contrast effect from different sized microbubbles i s investigated both theoretically and experimentally. Theoretically, t he reference back;scattered power is defined to evaluate the contrast effect of different sized microbubbles dispersed in the heart. in this study, the calculation results of two kinds of microbubbles of sizes 35 mu m and 2.2 mu m are discussed. From the calculation results obtai ned, it is found that the contrast effect from microbubbles of size 35 pm is better than that from microbubbles of size 2.2 mu m. The reason being that as the size of microbubbles decreases, a large portion of ultrasonic energy is lost due to absorption. Based on the same reason, microbubbles less than 10 mu m will cause an acoustic shadowing effec t at a higher concentration of microbubbles, according to the calculat ion results. Experimentally, microbubbles of an average size of 35 mu m are produced, and by filtration, microbubbles of an average size of 2.1 mu m are collected. Then, the contrast effect produced from microb ubbles before and after filtration are compared. It is observed that f or both kinds of microbubbles, a good contrast effect is observed at a relatively low concentration of microbubble dispersion. However, dist ortion of images occurs at high concentrations. The acoustic shadowing effect is observed fur microbubbles of an average size of 2.1 mu m wh ich can also be expected from the calculation results. On the other ha nd, the multiple-scattering effect which results in blurred images, oc curs For microbubbles of an average size of 35 mu m.