Background Targeted iron oxide nanoparticles are easily detected with MR by their exaggerated signal dropout. Recent advanced techniques are emerging to visualize iron oxide particles as hot spots rather than signal dearth. For background blood pool clearance, a typical delay of 24 hr is required between contrast treatment and imaging. Although targeted USPIO or MION agents bind endothelial cell surface markers, they also further extravasate into plaque, binding macrophages or other intraplaque constituents during the 24-hour wait. This confounds the morphological source of the MR signal. Moreover, in coronary MR imaging_where high temporal and spatial resolution are required and inherent anatomic magnetic susceptibility heterogeneity masks that of the iron oxide agents_dark spot T2-weighted gradient echo imaging of targeted iron oxides is challenging and has not yet been demonstrated. The objective of this research was to develop an intravascular, fibrin-specific iron oxide agent useful for early, rapid detection and quantification of ruptured plaque in coronary arteries with MRI.