A new technique for measuring the relaxation times T1 and T2 and the equilibrium magnetization M0 of slowly relaxing systems with weak NMR signals

Abstract

Pulse techniques are described for NMR lines with relaxation times T 1 and T 2 long compared with the decay time T 2 ∗ of the free induction signal after an rf pulse. The dependence of the amplitude of the steady-state free precession NMR signal between periodic rf pulses spaced by T⪡ T 1, T 2 on the flip angle φ by the rf pulses yields the ratio of the relaxation times T 1 T 2 as well as the equilibrium magnetization M 0. No equipment besides a normal Fourier spectrometer is necessary. By another type of experiment, the buildup of the steady state is recorded. In optimum circumstances, this steady state is built up exponentially with the time constant T ∗ = (T 1 + T 2) 2 . To perform such an experiment, the computer of the Fourier spectrometer must be furnished with a mass-storage device or a sufficiently large memory, the capability of which should be about ten times the storage area used for the data to be Fourier transformed in a normal experiment. By combining the results of both experiments, the relaxation times T 1, and T 2 can be determined within a minimum measuring time. Systematic errors caused by the inhomogeneity of the static and of the rf magnetic fields and their avoidance are discussed in detail.