(482b) Molecular Insights into NMR Relaxation of Gd(III)-Based Contrast Agents for MRI Applications

Nuclear magnetic resonance (NMR) relaxation is a powerful tool for probing matter non-destructively, with applications spanning oil recovery to material science to medicine. In this work, we seek to investigate NMR relaxation in the presence of gadolinium (III), which is a paramagnetic species used in MRI contrast agents. Gd(III) is a highly charged ion and here we model its interaction with liquid water using the AMOEBA polarizable forcefield. We carry out first-of-its-kind long time-scale molecular dynamics simulations of this system using GPU-acceleration. At frequencies relevant to MRI, our simulations of NMR relaxivity show good agreement with experiments, without any free parameters in the interpretation of the simulations. This is stark contrast to the extended Solomon-Bloembergen-Morgan (SBM) model which is the mainstay for interpreting relaxation in MRI.

A crucial ingredient in our approach is a way to model the relaxation for long times. We do this by decomposing the autocorrelation into contributions from different exponentially-relaxing modes. This allows us to model the response to long times and provides physical insights into the molecular-scale dynamics underlying relaxation. Being able to reconstruct NMR relaxation using molecular modes can prove transformative in practical applications. Having established our methods for Gd(III) at one temperature, we explore temperature effects and the role of chelating agents. In this talk, we will also discuss our efforts to develop forcefield parameters for the chelating agents using ab initio simulations.