Predicting the effect of relaxation during frequency-selective adiabatic pulses.

Autor: Pfaff AR; Department of Chemistry, Missouri University of Science & Technology, 400 West 11th, Rolla, MO 65409-0010, USA. Electronic address: arpvdc@mst.edu., McKee CE; Department of Chemistry, Missouri University of Science & Technology, 400 West 11th, Rolla, MO 65409-0010, USA. Electronic address: cemy8b@mst.edu., Woelk K; Department of Chemistry, Missouri University of Science & Technology, 400 West 11th, Rolla, MO 65409-0010, USA. Electronic address: woelk@mst.edu.
Jazyk: angličtina
Zdroj: Journal of magnetic resonance (San Diego, Calif. : 1997) [J Magn Reson] 2017 Nov; Vol. 284, pp. 99-103. Date of Electronic Publication: 2017 Oct 03.
DOI: 10.1016/j.jmr.2017.09.014
Abstrakt: Adiabatic half and full passages are invaluable for achieving uniform, B 1 -insensitive excitation or inversion of macroscopic magnetization across a well-defined range of NMR frequencies. To accomplish narrow frequency ranges with adiabatic pulses (<100Hz), long pulse durations at low RF power levels are necessary, and relaxation during these pulses may no longer be negligible. A numerical, discrete recursive combination of the Bloch equations for longitudinal and transverse relaxation with the optimized equation for adiabatic angular motion of magnetization is used to calculate the trajectory of magnetization including its relaxation during adiabatic hyperbolic secant pulses. The agreement of computer-calculated data with experimental results demonstrates that, in non-viscous, small-molecule fluids, it is possible to model magnetization and relaxation by considering standard T 1 and T 2 relaxation in the traditional rotating frame. The proposed model is aimed at performance optimizations of applications in which these pulses are employed. It differs from previous reports which focused on short high-power adiabatic pulses and relaxation that is governed by dipole-dipole interactions, cross polarization, or chemical exchange.
(Copyright © 2017 Elsevier Inc. All rights reserved.)
Databáze: MEDLINE
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