Magnetite nanodiscs as vortex-enhanced MRI contrast agents: a novel approach in medical imaging

Magnetic nanodiscs (MNDs) represent a transformative class of anisotropic magnetic nanoparticles with intrinsic vortex magnetization, enabling multifunctional applications in biomedical imaging and therapy. Here, we demonstrate their potential as dual-mode magnetic resonance (MR) contrast agents, a unique feature which is enabled by the high longitudinal relaxivity (r ₁ ≈ 40 mM^-1 s^-1) at ultralow magnetic fields (<70 µT) in combination with strong transverse relaxivity (r ₂ > 150 mM^-1 s^-1) at ultrahigh fields (>7 T). This field-dependent relaxivity profile uniquely positions MNDs as versatile T ₁/T ₂ agents compatible with emerging low-field MRI platforms and high-resolution clinical systems. Ex vivo and in vivo assessments confirmed clear anatomical localization and preferential hepatic accumulation, suggesting prolonged circulation times due to surface-mediated immune evasion. These properties highlight MNDs as promising candidates for next-generation theranostics, with tunable magnetic responses, high contrast efficiency, and the ability to synergize imaging and neurostimulation.