the invention relates to the use of biocompatible superparamagnetic nanoparticles comprising an inorganic core and a coating including an electrically charged polymer , and having low tissue and vascular adhesion , for use as contrast agents in magnetic resonance imaging . the aforementioned nanoparticles have novel pharmacokinetic and relaxability t2 * properties , with high potential for use in in vivo tissue imaging and tumour perfusion strategies based on parameter t2 *.