v 3-Integrin is a well-recognized biomarker of angiogenesis expressed on activated endothelial cells. It is a critical element in vascular restenosis where its upregulation by balloon overstretch injury promotes cell adhesion to the damaged extracellular matrix, induces extracellular metalloproteinase expression, and facilitates smooth muscle cell migration. We have conducted a series of in vivo studies in which v 3-integrin was detected by MRI (1.5T) as an early biomarker of nascent tumor growth (Vx-2 in rabbit and melanoma mice), early atherosclerosis in cholesterol-fed rabbits, and balloon overstretch-injury patterns in pigs. Paramagnetic nanoparticles covalentlycomplexed to a peptidomimetic v 3-integrin ligand were produced by microfluidization. Nontargeted paramagnetic nanoparticles and v 3-targeted nonparamagnetic nanoparticles were produced identically for control and competition studies. New Zealand White (NZW) rabbits implanted with nascent Vx-2 tumors and mice implanted with C-32 melanoma were treated systemically with v 3-integrin targeted paramagnetic nanoparticles that specifically bound and significantly enhanced (p 0.05) the MRI signal in the developing neovasculature after 2 hours (125% and 177%, respectively). Competitive blockage of v 3-integrin sites with v 3 targeted nonparamagnetic nanoparticles greatly ( 50%) diminished contrast signal enhancement (p 0.05) in both model systems. In cholesterol-fed NZW rabbits, black-blood MRI of the abdominal aorta v 3-targeted nanoparticles localized to angiogenic vessels in the expanding vaso-vasorum and produced enhanced signal (p 0.05) compared with nontargeted nanoparticles or control diet animals. In competition studies MRI enhancement was blunted, which confirmed the specificity of v 3-targeted nanoparticles. Furthermore, delayed enhancement (20 min) after injection of Gd-DTPA could not identify these early atherosclerotic changes. Finally, carotid arteries of pigs subjected to balloonoverstretch injury were treated locally with v 3 targeted, paramagnetic nanoparticles, saline or the nontargeted control. Contrast enhancement with v 3-targeted paramagnetic nanoparticles was dramatic and revealed asymmetrical patterns of balloon injury that were 50% greater than the actual balloon length and allowed the volume of vascular injury to be computed (955 234 mm2). No enhancement was discernible for the injured control vessels. v 3-Targeted paramagnetic nanoparticles provide a versatile molecular imaging platform useful for delineating vascular injury, diagnosing early atherosclerosis, and detecting nascent cancers with clinically relevant MRI systems (1.5 T). Early detection, effective therapy and sensitive longitudinal follow-up of these major disease processes with new molecular techniques could serve to noninvasively characterize and ameliorate their morbidity and mortality.