The efficiency of a given paramagnetic complex is closely
related to its relaxivity. Relaxivity is the result of a complex interplay between the
paramagnetic center’s structural, dynamic, and electronic properties. Good estimates of the
determinants of the relaxivity of a given paramagnetic complex can be obtained from the analysis
of relaxivity data as a function of the applied magnetic field (NMRD profiles).
High relaxivities can be attained, at the clinical field strength of 0.5-1.5 T, by lengthening the
molecular reorientational time, τR. Therefore, macromolecular systems were addressed by either the covalent or noncovalent
binding of paramagnetic chelates to slowly moving substrates
[Gianolio E. et al 2014].
Another opportunity to increase relaxivity is related to the use of bis-hydrated, but still highly-stable,
[Vagner A et al. 2016].