Introduction to the special issue on ultrasound contrast agents and targeted drug delivery

Targeted drug delivery (delivery of a drug to a spatially localized site in the human body) is one of the most ambitious goals of modern therapy. The strict localization of the pharmacological activity of a drug to the site of pathology would result in a significant reduction in systemic drug toxicity. This would enable the ability to deliver increased doses of drug to desired tissue, and thus would result in an increase in treatment efficacy and safety. Although a great amount of work is conducted worldwide on the research of various targeted drug delivery systems, clinical applications of site-targeted delivery are still very limited. In recent years, new promising possibilities for targeted drug delivery have been discovered based on the combination of ultrasound and microbubbles.