Renal clearable exceedingly small amorphous iron oxide nanoclusters for high-resolution T₁ magnetic resonance

Magnetic resonance imaging (MRI) is crucial for visualizing soft tissues and organs. Although gadolinium-based contrast agents (Magnevist, Gd-DTPA), which are commonly used in clinical MRI, their safety and resolution are still limited in practical applications. Herein, we present the preparation of exceedingly small amorphous iron oxide nanoclusters (ES-AIONCs) with properties characteristic of amorphous, exhibiting enhanced T₁ MRI contrast (r₁ = 8.1 mM^-1 s^-1) than that of Gd-DTPA (r₁ = 3.9 mM^-1 s^-1) under the 7 T magnetic field. The high r₁ value of ES-AIONCs enables them to increase the T₁-weighted MRI signal in the murine model of xenograft tumors by 64.7%, which is even a little higher than the value of Gd-DTPA (52.3%) at 7 T MRI instrument. Additionally, the stability of the ES-AIONCs towards biodegradation, is significantly reduced, leading to rapid breakdown and clearance when administered intravenously. This combination of properties directly addresses two outstanding needs in T₁ magnetic resonance imaging: the need for increased MRI resolution and the need to avoid bioaccumulation of imaging nanoparticles for reasons related to both patient safety and quality of future images.