SIMULATIONS OF CONTRAST EFFECTS FROM FREE MICROBUBBLES IN RELATION TOTHEIR SIZE, CONCENTRATION AND ACOUSTIC PROPERTIES

To gain a deeper in sight into the diagnostic images produced by micro bubbles as ultrasound contrast agents, the basic acoustical properties such as the scattering cross section, extinction cross section and th e expected backscattered power from different sized microbubbles are c alculated. The results proved that the ratio of scattering to extincti on cross section, size and concentration of microbubbles are the facto rs determining the maximum backscattered power received from microbubb le dispersions. When microbubbles decrease in size, the energy loss by microbubbles upon ultrasound exposure gradually changes from loss by scattering to loss by absorption. As a result, the concentration of mi crobubbles required to produce a B mode image of the comparable bright ness is increased. However, an increased concentration of microbubbles does not necessarily produce a clearer image. In this paper, it is fu rther established that an optimum concentration exists at which the mi crobubbles give maximum backscattered power. The optimum microbubble c oncentration and the maximum backscattered power also depend on the de pth of the microbubbles in the microbubble dispersion. In addition, th e concentration of microbubbles necessary to produce the maximum backs cattered power during resonance is less than that at other frequencies .