Constant-adiabaticity ultralow magnetic field manipulations of parahydrogen-induced polarization: application to an AA'X spin system.

Bogdan A Rodin,Konstantin L Ivanov,Román Picazo-Frutos,Dmitry Budker,Kirill F Sheberstov,James Eills

doi:10.1039/d0cp06581a

Abstract

The field of magnetic resonance imaging with hyperpolarized contrast agents is rapidly expanding, and parahydrogen-induced polarization (PHIP) is emerging as an inexpensive and easy-to-implement method for generating the required hyperpolarized biomolecules. Hydrogenative PHIP delivers hyperpolarized proton spin order to a substrate via chemical addition of H2 in the spin-singlet state, but it is typically necessary to transfer the proton polarization to a heteronucleus (usually 13C) which has a longer spin lifetime. Adiabatic ultralow magnetic field manipulations can be used to induce the polarization transfer, but this is necessarily a slow process, which is undesirable since the spins continually relax back to thermal equilibrium. Here we demonstrate two constant-adiabaticity field sweep methods, one in which the field passes through zero, and one in which the field is swept from zero, for optimal polarization transfer on a model AA'X spin system, [1-13C]fumarate. We introduce a method for calculating the constant-adiabaticity magnetic field sweeps, and demonstrate that they enable approximately one order of magnitude faster spin-order conversion compared to linear sweeps. The present method can thus be utilized to manipulate nonthermal order in heteronuclear spin systems.

Highlights

Nuclear magnetic resonance (NMR) methods suffer from notoriously low sensitivity, which mostly limits the scope of magnetic resonance imaging (MRI) to observing water or fat molecules in the body
By exploiting the constraint of ‘‘constant adiabaticity’’ we are able to increase the rate of spin-order transformations in nuclear spin systems
The theoretical approaches discussed here are of a general scope, and they can be applied to a variety of NMR experiments

Summary

Introduction

Nuclear magnetic resonance (NMR) methods suffer from notoriously low sensitivity, which mostly limits the scope of magnetic resonance imaging (MRI) to observing water or fat molecules in the body To overcome this limitation, hyperpolarization methods have been developed, allowing molecules to be produced with NMR signal enhancements on the order of 105 to 106 in a typical MRI scanner.[1,2,3] This enables the detection of chemical species in vivo at much lower concentrations than would otherwise be possible, and this has allowed for biochemical reactions in the body to be tracked in real time.[4,5,6] Fumarate is a metabolite that has been employed as a hyperpolarized biomarker; its rapid conversion to malate in vivo is indicative of cell necrosis.. The magnetic interaction that induces symmetry breaking is typically a chemical shift difference, or inequivalent J-couplings to a third nucleus

Methods

Results

Conclusion