Abstract
Hyperpolarization‐enhanced magnetic resonance imaging can be used to study biomolecular processes in the body, but typically requires nuclei such as 13C, 15N, or 129Xe due to their long spin‐polarization lifetimes and the absence of a proton‐background signal from water and fat in the images. Here we present a novel type of 1H imaging, in which hyperpolarized spin order is locked in a nonmagnetic long‐lived correlated (singlet) state, and is only liberated for imaging by a specific biochemical reaction. In this work we produce hyperpolarized fumarate via chemical reaction of a precursor molecule with para‐enriched hydrogen gas, and the proton singlet order in fumarate is released as antiphase NMR signals by enzymatic conversion to malate in D2O. Using this model system we show two pulse sequences to rephase the NMR signals for imaging and suppress the background signals from water. The hyperpolarization‐enhanced 1H‐imaging modality presented here can allow for hyperpolarized imaging without the need for low‐abundance, low‐sensitivity heteronuclei.
Highlights
Magnetic resonance imaging (MRI) is a powerful clinical technique most commonly used to produce structural images of the human body from observation of water and fat molecules, which are detectable because of their relatively high concentration
Pulse sequence optimization To optimise the parameters of the two of-phase echo (OPE) sequences, experiments were performed on a sample of malate-D2 in D2O at thermal equilibrium
parahydrogen induced polarization (PHIP) shuttling experiments To demonstrate the pulse sequences in hyperpolarized nuclear magnetic resonance (NMR) experiments we used the following procedure: (1) bubble para-enriched hydrogen gas into the precursor solution to produce hyperpolarized fumarate; (2) pneumatically shuttle the sample into an NMR tube containing fumarase in D2O held in an 11.7 T magnet; (3) apply either OPE-45, OPE-s90, or a 45° pulse every 4 s and detect the resulting NMR signal
Summary
Magnetic resonance imaging (MRI) is a powerful clinical technique most commonly used to produce structural images of the human body from observation of water and fat molecules, which are detectable because of their relatively high concentration. Recent advances in the field of hyperpolarization-enhanced nuclear magnetic resonance (NMR) have made it possible to produce metabolites with NMR signal enhancements of 104-105 1–15. One example of such a hyperpolarization method is parahydrogen induced polarization (PHIP) in which hydrogen gas enriched in the para spin isomer is chemically reacted with an unsaturated molecule to generate a product with hyperpolarized 1H nuclear spins[16,17,18,19,20,21,22,23,24,25]. PHIP is renowned for being inexpensive, simple to use, and allows for the production of hyperpolarized substrates with a high repetition cycle
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