T ₁ contrast agents based on Mn(II) were conjugated on amphiphilic dextran micelles via click chemistry. The obtained paramagnetic nanomicelle contrast agent has a higher T₁ relaxivity (13.3 Mn mmol⁻¹ s⁻¹) and better sensitivity than those of free Mn(II) complexes. Studies carried out in vivo suggest that this contrast agent has a better and long-acting vascular enhancement effect at a lower manganese dosage (0.1 Mn mmol kg⁻¹ BW).