NMR relaxometry: Spin lattice relaxation times in the laboratory frame versus spin lattice relaxation times in the rotating frame

Relaxometry dispersion curves display the spin lattice relaxation rate as a function of the measurement frequency. However, as far as proton NMR is considered, dispersion curves usually start around 5 kHz and thus miss the very low frequency region. This gap can be filled by the measurement of the spin–lattice relaxation rate in the rotating frame. The issue of connecting both relaxation rates is considered for two relaxation mechanisms: (i) randomly varying magnetic fields, (ii) dipolar interaction within a system of two equivalent spins. Appropriate data processing is presented and the random field mechanism turns out to be adequate.