Predicting the Effect of Relaxation during Frequency-Selective Adiabatic Pulses
Adiabatic half and full passages are invaluable for achieving uniform, B1-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 T1 and T2 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.
A. R. Pfaff et al., "Predicting the Effect of Relaxation during Frequency-Selective Adiabatic Pulses," Journal of Magnetic Resonance, vol. 284, pp. 99-103, Elsevier, Nov 2017.
The definitive version is available at https://doi.org/10.1016/j.jmr.2017.09.014
Keywords and Phrases
Adiabatic pulse; Hyperbolic secant pulse; Pulse sequence optimization; Relaxation; Solvent suppression
International Standard Serial Number (ISSN)
Article - Journal
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