Ultrasonic contrast agent, process for producing the same, and its use as diagnostic and therapeutic agent

PROBLEM TO BE SOLVED: To obtain the subject ultrasonic contrast agent that consists of, as basic components, amylose, a gas, and an organic liquid, has a constant and reproducible volume, markedly long life and good compatibility without allergic power and can be enriched in liver or the like. SOLUTION: The objective contrast agent consists of microparticles containing (A) amylose (suitable cyclodextrin and its derivative), (B) a gas (for example, air or nitrogen) and/or an organic liquid boiling at a temperature lower than 60 deg.C (suitably methylene chloride, isopentane. The microparticles comprising the component A is preferably coated wit a matrix of a polymer structure. In the case that the contrast agent is adjusted in its physiological osmotic pressure, an osmotically active substance as sodium chloride or galactose may be added. These microparticles are prepared as a clathrate, for example, by adding isopentane to saturated β-cyclodextrin solution at 10 deg.C, stirring the mixture in an ultrasonic bath, and freeze-drying the precipitation of the resultant slightly soluble complex.