The inherently low signal-to-noise ratio of NMR and MRI is now being addressed by hyperpolarization methods. For example, iridium-based catalysts that reversibly bind both parahydrogen and ligands in solution can hyperpolarize protons (SABRE) or heteronuclei (X-SABRE) on a wide variety of ligands, using a complex interplay of spin dynamics and chemical exchange processes, with common signal enhancements between 103−104. This does not approach obvious theoretical limits, and further enhancement would be valuable in many applications (such as imaging mM concentration species in vivo). Most SABRE/X-SABRE implementations require far lower fields (μT−mT) than standard magnetic resonance (>1T), and this gives an additional degree of freedom: the ability to fully modulate fields in three dimensions. However, this has been underexplored because the standard simplifying theoretical assumptions in magnetic resonance need to be revisited. Here we take a different approach, an evolutionary strategy algorithm for numerical optimization, Multi-Axis Computer-aided HEteronuclear Transfer Enhancement for SABRE (MACHETE-SABRE). We find nonintuitive but highly efficient multi-axial pulse sequences which experimentally can produce a 10-fold improvement in polarization over continuous excitation. This approach optimizes polarization differently than traditional methods, thus gaining extra efficiency.
@article{arxiv.2311.01417,
title = {Multi-axis fields boost SABRE hyperpolarization via new strategies},
author = {Jacob R. Lindale and Loren L. Smith and Mathew W. Mammen and Shannon L. Eriksson and Lucas Everhart and Warren S. Warren},
journal= {arXiv preprint arXiv:2311.01417},
year = {2023}
}