Researchers have developed a method for quantitatively assessing atherosclerotic plaque buildup in mice. They transplanted X-ray-irradiated low-density-lipoprotein-knockout mice with bone marrow cells expressing near-infrared fluorescent protein, which subsequently developed into fluorescent macrophages. These macrophages congregated specifically in atherosclerotic plaques that arose after feeding on a high-cholesterol diet. In vivo imaging detected the amount of aortic plaque formed and its change over time, which could help in assessing the efficacy of anti-atherosclerotic drugs.