Simulation of radio-frequency field inhomogeneity effects: application to pulse trains aimed at the determination of CSA-dipolar interference terms

摘要

The cross-correlation relaxation rate constant between dipolar interaction and chemical shift anisotropy (interference term) is of considerable interest for structural and dynamical determinations. The present study focuses on methods related to its impact on longitudinal nuclear relaxation, and especially to a procedure based on the applications of a train of pi pulses applied to both nuclei involved in such a process (Levitt MH, Di Bari L. Bull. Magn. Reson. 1994; 16: 94-114). The resulting steady state leads, in principle, to a straightforward determination of the relevant interference term. Simulations taking into account inhomogeneity of the radio-frequency (RF) field show that artifacts are responsible for instabilities which in practice preclude such a determination. An alternative method making use of a very limited number of RF pulses, combined with an appropriate filter, proves to be rather robust in view of achieving a proper measurement of the required interference term. Copyright (C) 2003 John Wiley Sons, Ltd. [References: 20]