Driven Equilibrium Methods for Enhancement of Nuclear Transients

Abstract

Several pulsed NMR experiments using rapidly repeating pulse sequences are described. Theoretical results for magnetization as a function of pulse spacing T are given for cases where the Bloch equations apply, and compared with experiments. These results suggest a simple method of rapid signal accumulation when T 2*<T2, T I , that is, when resolution is limited by magnet inhomogeneity.

Spin Dynamics of Carr–Purcell–Meiboom–Gill-like Sequences in Grossly Inhomogeneous B0 and B1 Fields and Application to NMR Well Logging

“…[28] does not contribute to the signal. The relevant first term has a form analogous to the expression for the magnetization in the absence of relaxation, Eq.…”

“…In inhomogeneous fields, the offset of the signal at the nominal echo center tends to be small, because n y n z is a rapidly oscillating function with respect to ⌬ 0 . However, this term describes the "steady-state-free-precession" signal (27,28) in inhomogeneous fields that can be observed before and after the nominal 180°RF pulses.…”

“…The solid line shows the result of solving the full spin dynamics problem, Eq. [28], numerically for the field maps of the NMR logging tool using the relaxation parameters T 2 ϭ 30 ms and T 1 ϭ 90 ms. The echo spacing was set to t E ϭ 1 ms and standard phase cycling was used.…”

Simulation of steady-state NMR of coupled systems using Liouville space and computer algebra methods

“…(17), (18), and (20) for a single spin system into Eq. (16), and applying the detection method from Eq. (3), we get the approximate measured signal at the time point b in the x-y plane:…”

“…Carr described the steady-state free-precession (SSFP) method in 1958 [4]. Artifacts from fast pulsing in Fourier transform NMR were recognized as steady-state effects by Freeman and Hill [15] and more general steady states were analyzed [16]. More recently, steady-state methods in medical imaging have led to much faster acquisitions, even real-time imaging [17][18][19][20][21].…”