Concurrent J-Evolving Refocusing Pulses

TL;DR

This paper introduces a novel J-evolving refocusing pulse design that incorporates coupling evolution, improving coherence transfer efficiency in heteronuclear sequences through optimal control theory.

Contribution

It presents a new pulse sandwich design based on the ICEBERG principle that accounts for J-coupling, enhancing refocusing performance over conventional methods.

Findings

J-evolving pulses outperform traditional refocusing pulses in simulations.

Optimized pulses show improved coherence transfer times.

Efficient J-compensated pulse sandwiches are also developed.

Abstract

Conventional refocusing pulses are optimised for a single spin without considering any type of coupling. However, despite the fact that most couplings will result in undesired distortions, refocusing in delay-pulse-delay-type sequences with desired heteronuclear coherence transfer might be enhanced considerably by including coupling evolution into pulse design. We provide a proof of principle study for a Hydrogen-Carbon refocusing pulse sandwich with inherent J-evolution following the previously reported ICEBERG-principle with improved performance in terms of refocusing performance and/or overall effective coherence transfer time. Pulses are optimised using optimal control theory with a newly derived quality factor and z-controls as an efficient tool to speed up calculations. Pulses are characterised in detail and compared to conventional concurrent refocusing pulses, clearly showing an improvement for the J-evolving pulse sandwich. As a side-product, also efficient J-compensated refocusing pulse sandwiches -- termed BUBU pulses following the nomenclature of previous J-compensated BUBI and BEBE(tr) pulse sandwiches -- have been optimised.