Myocardial infarction (MI) from atherosclerotic plaque rupture is a leading cause of death worldwide. Coronary plaques with a high macrophage count are at increased risk of rupture, however, in vivo identification of macrophages within coronary atherosclerosis remains challenging. Optical coherence tomography (OCT) provides detailed anatomical resolution of the coronary vessels during angiography and Ferumoxytol consists of ultrasmall superparamagnetic particles of iron oxide (USPIOs) that are taken up by macrophages. Given their metallic, reflective properties, we propose USPIO will substantially improve the present ability of OCT to identify coronary plaque macrophages. If successful, this technique may allow early identification of patients with atherosclerotic plaque prone to rupture and facilitate significant reductions in cardiovascular morbidity and mortality.