Predicting the effect of relaxation during frequency-selective adiabatic pulses

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Magnetic Resonance Imaging (MRI)

Background:

• Adiabatic pulses are crucial for B1-insensitive excitation and inversion in NMR.
• Achieving narrow frequency ranges with adiabatic pulses requires long durations and low RF power, making relaxation effects significant.

Purpose of the Study:

• To develop and validate a numerical model for magnetization and relaxation during adiabatic hyperbolic secant pulses.
• To investigate the impact of T1 and T2 relaxation on adiabatic pulse performance in small-molecule fluids.

Main Methods:

• A numerical model combining Bloch equations for relaxation with adiabatic angular motion equations was developed.
• The model calculates magnetization trajectories, including relaxation, during adiabatic hyperbolic secant pulses.
• Computer simulations were compared with experimental results in non-viscous, small-molecule fluids.

Main Results:

• The numerical model accurately predicts magnetization and relaxation behavior during adiabatic pulses.
• Standard T1 and T2 relaxation in the rotating frame effectively models these effects in the studied fluids.
• The model's agreement with experimental data validates its applicability.

Conclusions:

• It is feasible to model magnetization and relaxation during adiabatic pulses using standard T1 and T2 relaxation parameters.
• The proposed model enhances the performance optimization of applications utilizing adiabatic pulses.
• This approach differs from prior work focusing on high-power pulses and complex relaxation mechanisms.