Molecular imaging with targeted ultrasound contrast agents

The emerging field of "molecular imaging" refers to in vivo diagnosis of complex pathological processes by specific detection of unique molecular signatures of disease states either at the cellular, subcellular, or gene level. Identification of specific molecular epitopes causally associated with pathologies can be accomplished with the use of various novel targeted contrast agents, which permit conjunctive delivery and local deposition of therapeutic agents directly at the site of disease. Combining imaging with drug delivery provides verification of drug delivery and quantification of treatment, serving in effect as a new paradigm for rational drug dosing. Important potential clinical applications for targeted contrast agents include: 1) characterization of vulnerable plaques by detection of microscopic deposits of fibrin in plaque fissures prior to rupture, 2) early detection and treatment of solid tumors and metastases (colon, breast, prostate, etc.) by localization of angiogenesis, 3) detection of early atherosclerosis by assessment of epitopes related to macrophage trafficking (e.g., VCAM), and 4) diagnosis and treatment of inflammatory pathologies (infection, arthritis, myocarditis, transplant rejection, etc.) by delineation of epitopes that are markers for inflammatory cell recruitment (adhesion molecules, selectins, etc.). In this paper, we provide a brief review of the field and discuss specific applications.