FERRITE-CAPSULATED POROUS SILICA MICROSPHERES FOR ULTRASONIC CONTRASTAGENTS

Porous silica microspheres, similar to 2.2 mu m in average diameter, w ere encapsulated with magnetite (F3O4) by ferrite plating in an aqueou s solution of FeCl2 at 65 degrees C. Using the resultant ferrite-capsu lated particles as ultrasonographic contrast agents (in which air trap ped in the pores scatters ultrasonic waves), we tried to visualize sti ll and flowing waters in holes and a channel perforated in agar blocks by using a 7.5MHz B-mode echograph. Clear image enhancement was succe ssfully obtained only when the ferrite-capsulated particles were evapo rated in air before they were dispersed in the waters. This is because , during ferrite plating in the aqueous solution, the pores were perme ated with water, which was expelled by the evaporation and then, subst ituted by air when the particles were exposed to air again.