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.
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