Aim To synthetize a nuclear magnetic resonance imaging (MRI) nano contrast agent targeted to atherosclerosis (As) lesions, and to provide experimental evidence for the development of a new MRI diagnostic technique for As. Methods The self developed aptamer PM1, which was targeted to the foam cells, was coupled to iron oxide (Fe₃O₄) nanoparticles, and the target MRI contrast agent was prepared, named MRI-As. The As animal model of apolipoprotein E gene knockout (ApoE－/－) was established by feeding with high-fat diet. The As lesion of aorta was identified by Sudan red Ⅳ staining. Effect of MRI-As contrast agent on MRI imaging of plaque in As mice was detected by MRI imager. Results MRI imaging of the ApoE－/－ mice animal model showed that the aortic wall was rough. As lesions showed high signal intensity, which was well contrasted with the surrounding tissues. The central signal was higher, more uniform and the edge was clearer. After injection of MRI-As contrast agent, the signal intensity of As lesion area showed a downward trend, and the vascular wall was not smooth and showed the defect of multiple spot signal. After injection of MRI-As contrast agent in control group, the signal intensity of vascular wall did not change significantly. ConclusionsMRI-As contrast agent can play an active targeting to As lesions. Using the negative contrast effect of Fe₃O₄ nanoparticles on As lesions, MRI-As contrast agent significantly enhances the resolution of the MRI image of As lesion, and it has the potential of new, fast, efficient, non-invasive, non radiative contrast agent for As MRI image.