Characterization of metal-based nanoparticles as contrast agents for magnetic resonance imaging

Magnetic resonance imaging (MRI) has been recognized as one of the most important imaging techniques in medicine. However, without using contrast agents, the difference between diseased and normal tissues can be difficult to observe with MRI. Therefore, in this chapter, important aspects for the development of efficient and safe magnetic nanoparticle-based contrast agents for MRI will be discussed. First, basic mechanisms of MRI and spectroscopy will be described, such as relaxation times and contrast agent's relaxivity. Then the requirements for magnetic nanoparticles to act as efficient contrast agents will be listed, i.e., having high relaxivity. Relaxivity r2 and thus the contrast efficacy of superparamagnetic nanoparticles can be enhanced either via nanoparticle's magnetic properties or coating optimization. Both contributions will be described. In addition to enhanced contrast agent efficacy, the selected coating should provide excellent stability and biocompatibility as well. On the example of magneto-liposomes as efficient and biocompatible contrast agents, standard characterization procedures for the determination of samples relaxivities will be demonstrated. Finally, the future directions in the development of magnetic nanoparticle-based contrast agents will be given.