Molecular and supramolecular routes to enhance Gadolinium-based contrast agents relaxivity: How far are we from the theoretical optimal value?

ion, the ion's electronic relaxation time, molecular reorientation time, and the exchange rate of the coordinated water molecules. Understanding the key factors that affect relaxivity has enabled the design of systems with optimized structural and dynamic properties. However, some examples demonstrate exceptional relaxivity which cannot be fully explained by the established theory. In particular, GBCAs within confined environments show significant promise for developing high-relaxivity agents. Overall, one may state that nowadays it is possible to attain highly efficient GBCAs thanks to the in-depth understanding of the structural and dynamic determinants of their relaxivity, together with the optimization of their in vivo stability and biodistribution/excretion properties. This knowledge is crucial for the rational design of the next generation of MRI CAs. The domain of Molecular Imaging will also largely benefit from these efforts.