Targeted acoustic contrast agents: New opportunities for ultrasound in medical diagnosis and therapy

For 30 years, medical professionals have sought the ‘‘magic bullet’’ which would allow sensitive detection of disease and facilitate localized administration of potent chemotherapeutic agents without systemic toxicities. Ligand targeted ultrasonic contrast agents have the potential to improve diagnostic sensitivity, port drugs to specific pathologic tissues, and provide dosimetry of the delivered therapeutics. The authors have recently developed a ligand directed, lipid encapsulated perfluorocarbon emulsion particle (250‐nm diameter). These particles, when bound to biological surfaces, strikingly increase the acoustic reflectivity, although the particles have low inherent echogenicity. Contrast enhancement of the reflectivity of blood thrombi, fibrin clots, and nitrocellulose membranes has been tentatively explained by a transmission line model. Intravenous injection of the perfluorocarbon emulsion particles has localized and acoustically enhanced remote thrombi which were otherwise difficult to detect. The contrast agent has a 1‐h circulatory half‐life which greatly facilitates successful systemic targeting. The small particle size of these emulsions affords access to tiny capillary beds and vascular endothelial disruptions such as those following angioplasty. Collectively, these studies suggest perfluorocarbon contrast agents can target molecular epitopes within and proximate to the systemic circulation. These agents are creating new and exciting opportunities for ultrasound in medical diagnosis and therapy.