[Nanoparticles: the industrial viewpoint. Applications in diagnostic imaging]

Iron oxide particles can be divided into two categories: small superparamagnetic iron oxide (SPIO) and ultrasmall superparamagnetic iron oxide (USPIO). Both describe nanoparticles most often formulated with dextran or dextran derivatives. For magnetic resonance imaging, these agents are of major importance because of their superparamagnetic effect, that is the magnetic field generated locally by their presence. Clinical applications have been well differentiated: 1) SPIO (larger than 50nm) are mainly used via intravenous infusion to detect and characterize small focal lesions in the liver. SPIO can also be given orally to visualize the digestive tract; 2) USPIO (smaller than 50nm) have a longer plasmatic half-life (>36hours) and exhibit slower uptake by liver and spleen after intravenous administration. This allows the product to access macrophages in normal (lymph nodes) or diseased tissue (multiple sclerosis, graft rejection, atheroma plaques, stroke, rhumatoid arthritis). They can also be used as biomarkers to evaluate the efficacy of treatments. In addition to routine clinical applications, these agents are also under investigation to improve diagnoses in oncological, inflammatory and degenerative as well as cardiovascular diseases (risk of atheroma plaques).