This document discusses non-invasive imaging of macrophages for detection of vulnerable plaque using magnetic resonance imaging (MRI) with ultrasmall particles of iron oxide (USPIO). USPIOs are taken up by macrophages and shorten MRI relaxation time, allowing visualization of macrophage activity. Studies show USPIO uptake correlates with macrophage density and plaque inflammation in animal models. While MRI can identify plaque inflammation, limitations include poor resolution for coronary imaging and high cost compared to alternatives.