This document describes a study that introduces a non-invasive method for imaging macrophage infiltration in inflamed atherosclerotic plaques using superparamagnetic iron oxide (SPIO) nanoparticles and MRI. The researchers injected SPIO into hypercholesterolemic and normal rabbits and found that SPIO profoundly accumulated in areas of macrophage infiltration in the atherosclerotic plaques, as confirmed by histology. SPIO-enhanced MRI was able to identify these inflamed plaques non-invasively. The results suggest SPIO-enhanced MRI can be a novel method for detecting rupture-prone inflamed plaques associated with heart attacks and strokes.