The Fantastic Four: A plug 'n' play set of optimal control pulses for enhancing nmr spectroscopy

TL;DR

This paper introduces a set of four optimized, robust control pulses for NMR spectroscopy that can replace traditional hard pulses, significantly improving sequence performance with minimal modifications.

Contribution

The authors develop a universal set of four optimal control pulses that are easily substitutable for hard pulses in NMR sequences, enhancing robustness and performance.

Findings

Pulses provide uniform performance over large resonance offsets.

Pulses tolerate RF inhomogeneity and miscalibration.

Experimental sequences show significant performance improvements.

Abstract

We present highly robust, optimal control-based shaped pulses designed to replace all 90{\deg} and 180{\deg} hard pulses in a given pulse sequence for improved performance. Special attention was devoted to ensuring that the pulses can be simply substituted in a one-to-one fashion for the original hard pulses without any additional modification of the existing sequence. The set of four pulses for each nucleus therefore consists of 90{\deg} and 180{\deg} point-to-point (PP) and universal rotation (UR) pulses of identical duration. These 1 ms pulses provide uniform performance over resonance offsets of 20 kHz (1H) and 35 kHz (13C) and tolerate reasonably large radio frequency (RF) inhomogeneity/miscalibration of (+/-)15% (1H) and (+/-)10% (13C), making them especially suitable for NMR of small-to-medium-sized molecules (for which relaxation effects during the pulse are negligible) at an accessible and widely utilized spectrometer field strength of 600 MHz. The experimental performance of conventional hard-pulse sequences is shown to be greatly improved by incorporating the new pulses, each set referred to as the Fantastic Four (Fanta4).