This document summarizes studies examining methods to track macrophage recruitment into atherosclerotic plaques. Initial EM studies in pigs found bi-directional movement of foam cells through the endothelium. Subsequent studies labeled monocytes with fluorescent dyes or microspheres and tracked their recruitment to plaques in pigs and mice. A newer method used PCR to detect transfusion of male monocytes into female mice. The presented study examined the effects of cytokines on SPIO uptake in plaques of ApoE-deficient mice, finding greater iron particle deposition in cytokine-treated mice, indicating increased monocyte recruitment. This suggests SPIO could non-invasively monitor monocyte recruitment during MRI.