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

We have studied the magnetic behavior of a colloidal suspension consisting of dextran-coated Fe₃O₄ nanoparticles with average particle core size dc = 8 nm (hydrodynamic diameter dH =100 nm), used as contrast medium in clinical protocols for MRI (ENDOREM) for the detection of liver lesions. 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 (Fe₃O₄) is the preferred phase because of its large saturation magnetic moment (Ms ~ 82 emu/g for T = 300 K).