Abstract: Introduction Adiabatic techniques in NMR and EPR offer new opportunities to control and modulate spectra in magnetic resonance, which opens new doors for research in materials science, biology and chemistry. Adiabatic pulses are a class of amplitude- and frequency-modulated RF/microwave pulses that are relatively insensitive to magnetic field inhomogeneity and off-resonance effects. A notable feature of adiabatic inverting pulses is the possibility of rectangular spin inversion over a large frequency range, which allows their involvement in medical clinical MRI studies for sharper selection of spatial slices. At present, offset-independent amplitude (OIA) [1] pulses are among the most popular, with the adiabaticity parameter fixed for all isochromats of a given spectral contour, but only for a single moment of time, when the current frequency of the pulse coincides with the frequency of the corresponding isochromat. Despite their popularity, these pulses have poor performance in some cases, requiring high peak power of the B1 field amplitude and being sometimes completely inefficient. In a previous study [2], we proposed an alternative approach (CA) for constructing adiabatic pulses. This approach ensures constant adiabaticity for the central isochromat throughout the pulse and enhances efficiency, even in cases where the pulse duration is limited. Methods In this paper, we have developed inverting MCA pulses that combine CA and OIA opportunities. We derived and solved the differential equations for the time dependencies of the RF field amplitude and frequency offset, which provide these two conditions. We then studied and compared the spectral selectivity and stability of the constructed pulses by scaling the RF field amplitude with those of other popular adiabatic inverting pulses. The MCA pulses obtained exhibited notable stability and superior performance in comparison to other OIA pulses under conditions of low adiabaticity. Additionally, a script has been provided to generate a shape pulse file for the TopSpin program utilizing our adiabatic inverting pulse for incorporation into the experimental procedures [3]. The proposed MCA pulses were also verified experimentally on an NMR spectrometer, which confirms the numerical simulation results. Acknowledgements This work is supported by the Russian Science Foundation (Contract No. 23-73-10103).

Cite: Snadin A.V. , Kiryutin A.S. , Fishman N.N. , Lukzen N.N.
Development of a new class of adiabatic inverting MCA pulses combining constant and offset-independent adiabaticity
22nd International School-Conference MAGNETIC RESONANCE AND ITS APPLICATIONS 31 Mar - 4 Apr 2025