New physics model links molecular motion to MRI signals ^{CEFR B2}

Researchers at Rice University and Oak Ridge National Laboratory present a physics-based NMR eigenmodes framework in The Journal of Chemical Physics that links molecular-scale motion directly to the signals recorded by clinical MRI machines. The study examines common contrast agents—often a gadolinium ion inside an organic shell—and how they alter the relaxation of nearby water molecules, a key process for MRI contrast.

The framework solves the full physical equations for NMR relaxation in liquids by using the Fokker-Planck equation to track how probabilities of molecular positions and velocities evolve in time. From this solution the authors identify eigenmodes, the natural ways water molecules respond to contrast agents at the microscopic level. These modes provide a more detailed picture than earlier simplified models and allow the framework to reproduce experimental measurements at clinical MRI frequencies with high precision. The results show that many widely used simplified models are specific cases within a more complete theory.

The research grew out of detailed molecular dynamics simulations and helps to interpret both those simulations and experimental findings. The team released its code as open source to encourage wider use and further development. The study received support from the Ken Kennedy Institute, Rice Creative Ventures Fund, Robert A. Welch Foundation, and the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory.

• Possible applications include battery design.
• It may inform subsurface fluid flow and porous rock studies.
• It could also aid research on biological cells and materials science.