Superparamagnetic iron oxide particles: current state and future development

Abstract

A wide range of applications for superparamagnetic iron oxide (SPIO) particles as contrast media for MRI has emerged over the last 15 years. SPIO particles can be manufactured with different particle sizes and surface coatings. Large SPIO particles (50-150 nm) predominantly produce a signal decrease or T2 -shortening and are used as contrast media for MRI of the liver and spleen. They have a high accuracy, especially in detecting liver metastases (approved for clinical use: AMI-25 (Endorem or Ferridex), SHU-555A (Resovist)). Smaller particles (about 20 nm in diameter) show a different organ distribution and have a potential for improving noninvasive lymph node assessment or characterizing vulnerable atherosclerotic plaques (in clinical trials: AMI-227 [Sinerem or Combidex]). Particles with an optimized T1-relaxivity and prolonged intravascular circulation time can be used as blood pool contrast media for MR angiography. The currently investigated indications are MR angiography of the trunk, peripheral vessels, and coronary arteries (e.g., SHU-555 C (Supravist), VSOP-C 184). Other applications of small SPIO particles include MRI of the bone marrow and the determination of perfusion parameters in tumors or other tissues like the myocardium. SPIO particles with a modified coat can be used in so-called molecular imaging, such as receptor-directed imaging, cell labeling for in-vivo monitoring of cell migration, e.g., stem cell labeling, and labeling of gene constructs for localization in genetic therapy. In tumor therapy SPIO particles can serve as mediators for hyperthermia. SPIO is a powerful MR contrast medium with manifold applications ranging from diagnostic imaging to molecular medicine.