Behaviour of the NMR Relaxation Parameters at High Fields

The algebraic expressions of the dynamic NMR parameters, namely, the spin—lattice relaxation time T1, the spin-spin relaxation time T2, the cross-relaxation terms σ and σρ, and the NOE factor are derived. The study of their behaviour as a function of the applied magnetic field or resonance frequency is examined, with special emphasis on the high frequency region (ν > 800 MHz). The different models which may be used to derive the spectral density are presented. Several plots of the variation of the NMR dynamic parameters for the most often encountered nuclei (1H,13C,15N,31P) are shown. These plots correspond to different and realistic values of the correlation times, internuclear distances, and chemical shielding anisotropy. The variation of the NMR signal sensitivity as a function of the magnetic field is also discussed. As expected, with the exception of the phosphorus nucleus, the sensitivity increases with B0. In some cases, the increase is greater than the expected factor B 0 3/2 .