Contrast agents in MRI are used to accelerate the relaxation rate of solvent water molecules, with the goal of enhancing resolution. Traditionally, the Solomon-Bloembergen-Morgan equations have been utilized to describe relaxation times in terms, primarily of the Zeeman interaction. However, in complexes containing higher spins, such as Gadolinium(III) (where S=7/2) other interactions such as the Zero-Field Splitting(ZFS) begin to play a significant role. This research delves into an understanding of the relaxation process, focusing on the role of ZFS. Highly accurate ab-initio multiconfigurational methods have as yet, not been employed to theoretically determine the ZFS parameters in such complexes. As a first step towards this thesis, we have used these high-level methods to determine the ZFS parameters of Gd(III) complexes associated with clinically relevant complexes and compared the results to experiment.
