Relaxivity Enhancement of Hybrid Micelles via Modulation of Water Coordination Numbers for Magnetic Resonance Lymphography.

Considerable efforts have been made to develop nanoparticle-based magnetic resonance contrast agents (CAs) with high relaxivity. The prolonged rotational correlation time (τ R ) induced relaxivity enhancement is commonly recognized, while the effect of the water coordination numbers ( q ) on the relaxivity of nanoparticle-based CAs gets less attention. Herein, we first investigated the relationship between T 1 relaxivity ( r 1 ) and q in manganese-based hybrid micellar CAs and proposed a strategy to enhance the relaxivity by increasing q . Hybrid micelles with different ratios of amphiphilic manganese complex (MnL) and DSPE-PEG2000 were prepared, whose q values were evaluated by Oxygen-17-NMR spectroscopy. Micelles with lower manganese doping density exhibit increased q and enhanced relaxivity, corroborating the conception. In vivo sentinel lymph node (SLN) imaging demonstrates that DSPE-PEG/MnL micelles could differentiate metastatic SLN from inflammatory LN. Our strategy makes it feasible for relaxivity enhancement by modulating q , providing new approaches for the structural design of high-performance hybrid micellar CAs.