Ln-Based Particles as MRI Contrast Agents

Lanthanides have proven effective in enhancing the contrast of magnetic resonance images by modulating the intensity of the proton signal of water in close proximity. However, the low sensitivity of this imaging modality has stimulated the search for new MRI probes along with the already established small paramagnetic complexes. This is where nanoparticulate systems came into play, owing to their immense morphological diversity and their ability to accommodate and deliver high payloads of lanthanides to target sites through facile surface grafting with various functional molecules. Decades of dedicated research in this direction yielded fascinating examples of lanthanide-based nanoparticles with enhanced capabilities. These include responsiveness to diverse endogenous stimuli, multimodal imaging, and most importantly, the integration of imaging and therapeutic modalities. In this 296chapter, we review some examples of solid and porous lanthanide-based nanoparticles and the corresponding relaxation enhancement mechanisms, and discuss their applications, potential, limitations, and prospects.