Solvent 1H NMRD study of biotinylated paramagnetic liposomes containing Gd-bis-SDA-DTPA or Gd-DMPE-DTPA

The relaxometric properties of two biotinylated paramagnetic liposomes with different lipophilic complexes have been investigated by water proton nuclear magnetic resonance dispersion. The proton relaxivity was found to have a peak at the proton Larmor frequencies generally used in MRI, and to be largely affected by the residence lifetime of the water molecule in the coordination site of the metal chelate. The measurements also indicate that a local motion in the nanosecond time scale, i.e. much faster than the rotational time of the whole liposome, is effective. Possible explanations for this behavior are discussed, that may provide guidelines for the design of second-generation paramagnetic liposomes as contrast agents.