A Robust Freeman-Hill-inspired Pulse Protocol For Ringdown-free T1 Relaxation Measurements
A new difference-spectroscopy method is introduced for measuring T1 relaxation times. It is inspired by the earlier work of Freeman and Hill and eliminates the need for recording signal intensities at thermodynamic equilibrium. The new method is termed SIP-R (Split-Inversion Pulse and Recovery) and reduces the number of refinable parameters in the curve fitting process of relaxation-delay-dependent signal intensities by using two instead of the three parameters typically used in the standard inversion-recovery sequence. The SIP-R method preserves the dynamic range of measurement of the standard inversion-recovery method but converts the rise-to-maximum mathematical functionality of the recorded data into a decay-to-zero functionality. The decay-to-zero functionality renders the SIP-R sequence advantageous for inverse Laplace transformation numerical optimizations. The new technique proves to be extremely robust with respect to pulse imperfections, pulse-power changes during the pulse sequence, pulse-width miscalibrations, resonance offsets, and radiofrequency field variations. It also compensates for acoustic ring-down effects and proves reliable for measurements with inhomogeneously broadened signals up to several kilohertz linewidth. 1H NMR experiments with methane gas at pressures up to 50 atm in toroid-cavity pressure vessel probes and in the presence of the methane-to-methanol conversion catalyst Cu-ZnO/Al2O3 are used to show the usefulness of the new method for relaxation time investigations under pressure, at strong radiofrequency field gradients, and in the presence of paramagnetic materials.
Z. G. Mayes et al., "A Robust Freeman-Hill-inspired Pulse Protocol For Ringdown-free T1 Relaxation Measurements," Journal of Magnetic Resonance, vol. 352, article no. 107490, Elsevier, Jul 2023.
The definitive version is available at https://doi.org/10.1016/j.jmr.2023.107490
Keywords and Phrases
Acoustic ringing; Decay-to-zero functionality; Gas-phase NMR; Longitudinal relaxation; Paramagnetic material; Pressure probe; Pulse imperfections; Radiofrequency field gradient; Toroid cavity detector; Ultrawideline NMR
International Standard Serial Number (ISSN)
Article - Journal
© 2023 Elsevier, All rights reserved.
01 Jul 2023