Recent advances in lanthanide-based nanoparticle contrast agents for magnetic resonance imaging: Synthesis, characterization, and applications

MRI is a powerful, non-invasive imaging technique with exceptional soft tissue contrast, requiring contrast agents to enhance sensitivity by shortening longitudinal (T 1 ) and transverse (T 2 ) relaxation times. While most clinical agents are chelate-based, their potential toxicity has driven the development of nanoparticle-based alternatives. Nanoparticles offer reduced toxicity, improved stability, prolonged circulation time, and better control over surface properties. Lanthanide-based nanoparticles, in particular, are promising due to their paramagnetic properties enhancing MRI contrast. The design of these nanoparticles focuses on optimizing size, shape, and colloidal stability with advances in synthesis techniques allowing for precise control over particle size, morphology, and stability to significantly influence relaxivity. Larger sizes increase r₂ values but may reduce stability, while anisotropic shapes enhance relaxivity compared to the more stable spheres. Surface modifications with functional polymers improve stability and prevent aggregation, optimizing imaging performance. As research progresses, lanthanide-based nanoparticles are poised to become crucial tools in radiology-driven cancer diagnosis and therapy, offering dual functionality for early detection, targeted treatment, and minimized off-target effects. However, these nanoparticles must be refined for tumour-specific diagnostic and therapeutic applications and undergo comprehensive safety evaluations before clinical trials.