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Magnetic resonance imaging (MRI) is based on the excitation of protons in response to intense magnetic fields and radiofrequency pulses, providing high-resolution images and soft tissue contrast. MRI frequently employs contrast agents, with gadolinium (Gd3+) being the most common. However, free Gd3+ can accumulate in tissues, leading to toxic effects and nephrogenic systemic fibrosis (NSF), particularly in patients with renal dysfunction. A systematic review of the literature explores alternatives, such as superparamagnetic iron oxide nanoparticles (SPIONs), which have demonstrated higher relaxivity and lower toxicity in preclinical studies. Other options include nitroxide-based agents and zero-valent iron nanoparticles, which offer enhanced stability and biocompatibility. Despite promising advances, such as the functionalization of SPIONs for specific applications, challenges remain regarding long-term toxicity and technical limitations. The search for safer and more effective contrast agents remains essential to expanding the clinical applications of MRI.
