Magnetic Structure and Power Absorption in Magnetite Nanoparticles from a MRI Contrast Agent

摘要

Colloidal suspensions based on iron-oxide nanoparticles have gained significance in biomedical sciences as contrast agents (CA) for clinical protocols in Magnetic Resonance Imaging (MRI) and Magnetic Fluid Hyperthermia (MFH). The main action of CAs is to change the T1 and T2 relaxation rates of the protons within target tissues, to the extent that a change in signal intensity can be observed. The relaxation effect is proportional to the square of the saturation magnetic moment (MS) of the material to be employed, and therefore for these applications, magnetite (Fe{sub}3O{sub}4) is the preferred phase because of its large saturation magnetic moment (M{sub}S≈82emu/g for T=300K). For MFH therapy, the ability to absorb radiated power from an alternating field at low frequencies (<100kHz) depends on the loss component of the magnetic susceptibility, as well as the rheological properties of the target physiological medium (i.e. cell culture or tissue). To improve stability and biocompatibility the particles are coated with a polysaccharide and suspended in water-based solvents, although the effects of these coatings on the efficacy in MRI or MFH applications is still under debate. [1]