The sensitivity issue of MRI technique is related the intrinsic Relaxivity of a given Contrast Agent. The chemists have to design systems endowed with structural and dynamic properties that lead to optimized values for those parameters that are relevant for a given contrast enhancing mechanism. Much work has been done and is ongoing to design structures with high relaxivity.
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, Gd-complexes [Vagner A et al. 2016].