GD3-RESONANCE-IMAGING (MRI) - STUDIES USING O-17 NMR AND EPR AT SEVERAL MAGNETIC-FIELDS( CHELATES OF INTEREST IN MAGNETIC)

The combination of O-17 NMR relaxation rate and chemical shift measure ments and EPR linewidth measurements at several magnetic fields provid es a powerful probe of water exchange, rotational dynamics and electro nic relaxation in aqueous solutions of Gd3+ complexes. This informatio n is important for the understanding of the proton relaxivity of the c omplexes. Variable pressure measurements show a change of water exchan ge mechanism from associatively activated on [Gd(H2O)8]3+ and [Gd(PDTA )(H2O)2]- to probably limiting dissociative on the MRI contrast agents [Gd(DTPA)(H2O)]2-, [Gd(DOTA)(H2O)]- and [Gd(DTPA-BMA)(H2)O)]. This le ads to relatively slow water exchange rates on the latter three comple xes. For [Gd(DTPA-BMA)(H2O)], the exchange rate is sufficiently slow t o have an effect on the inner sphere proton relaxivity, and hence on t he interpretation of NMRD profiles.