Molecular imaging of macrophages in atherosclerosis

Activated macrophages play central roles in various stages of the pathogenesis of atherosclerosis. Particularly, the role macrophages play in the onset of acute thrombotic complications including myocardial infarction, a global health burden, has the large clinical impact. It is thus important to identify high-risk patients for these thrombotic complications to improve the prognosis by detecting macrophage- rich, subclinical lesions. In addition, macrophage imaging of vascular lesions in humans would facilitate understanding of the disease mechanisms and also help to monitor the effects of new therapies in the near future. These clinical needs have driven recent efforts on the development of molecular imaging modalities to visualize macrophages. Various imaging agents which are taken up by macrophages (e.g., superparamagnetic iron oxide for magnetic resonance imaging) or target a macrophage- specific biological process (e.g., proteinase activity for optical imaging) have become available. In the field of nuclear medicine, FDG-PET already has been in the stage of clinical trials. This chapter reviews current states and future perspectives of macrophage-targeted molecular imaging.