Live magnetic observation of parahydrogen hyperpolarization dynamics
arxiv(2024)
Abstract
Nuclear spin hyperpolarization is used in physics, chemistry, and medicine to
produce strong magnetization unachievable by equilibrium polarization
techniques. Hyperpolarization enables magnetic resonance spectroscopy and
imaging with minute samples, and is used to produce MRI spin-tracers and
polarized physics targets. Although widely used, the dynamics of the
hyperpolarization process have never been studied `live' due to the extremely
low (Hz-band) frequencies involved, and/or detector saturation by the driving
fields used. Here, we use an atomic magnetometer with sub-pT sensitivity to
observe, in real time, the complex dynamics of hyperpolarization, without
disturbing or disrupting the process. We start by examining
parahydrogen-induced ^1H and ^13C magnetization build-up during adiabatic
eigenbasis transformations in the μT-field avoided state crossings at the
heart of the process; we see live hyperpolarization dynamics including coherent
oscillations, leakage mechanisms and dipolar shifts that would be challenging
or impossible to observe by post hoc measurement. We then extend the methods to
observe the chemical-exchange-driven ^13C hyperpolarization of
[1-^13C]-pyruvate – the most important spin tracer for clinical metabolic
imaging. Beyond the interests of hyperpolarization, the observation of
adiabatic transitions in real-time is a fundamentally new approach to NMR,
reveals previously hidden nuclear spin dynamics and enables quantum control and
live process optimization in a variety of chemical scenarios.
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