NaDyF4 Nanoparticles as T2 Contrast Agents for Ultrahigh Field Magnetic Resonance Imaging

A major limitation of the commonly used clinical MRI contrast agents (CAs) suitable at lower magnetic field strengths (< 3.0 T) is their inefficiency at higher fields (> 7 T), where next-generation MRI scanners are going. We present dysprosium nanoparticles (beta-NaDyF4 NPs) as T-2 CM suitable at ultrahigh fields (9.4 T). These NPs effectively enhance T-2 contrast at 9.4 T, which is 10-fold higher than the clinically used T-2 CA (Resovist). Evaluation of the relaxivities at 3 and 9.4 T show that the T-2 contrast enhances with an increase in NP size and field strength. Specifically, the transverse relaxivity (r(2)) values at 9.4 T were similar to 64 times higher per NP (20.3 nm) and similar to 6 times higher per Dy3+ ion compared to that at 3 T, which is attributed to the Curie spin relaxation mechanism. These results and confirming phantom MR images demonstrate their effectiveness as T-2 CAs in ultrahigh field MRIs.