Magnetic Nanoparticles Used as Contrast Agents in MRI: Relaxometric Characterisation

Magnetic resonance imaging (MRI) has developed at an exponential rate over the last decades, and the development of contrast agents to enhance the visualization of organs has followed the same trend. Meanwhile, magnetic nanoparticles that generate either “positive” or “negative” contrast in MRI have become one of the most important biomedical applications of nanotechnology. Indeed, superparamagnetic iron oxide nanoparticles, as negative contrast agents for T ₂/T ₂ ^* -weighted imaging, have found numerous applications in preclinical and clinical MRI (cell labeling, vascular contrast, lymph node imaging, liver contrast). In addition to this, paramagnetic and antiferromagnetic nanoparticles based on the elements Gd³⁺ and Mn²⁺ have mainly been exploited in vascular procedures and targeted imaging, for their capacity to enhance the MR signal of blood and of molecular signatures of endovascular disease. They are commonly referred to as “positive” contrast agents for T ₁-weighted imaging.