NMR Hyperpolarization Techniques of Gases

Abstract

Nuclear spin polarization can be significantly increased through the process of hyperpolarization, leading to an increase in the sensitivity of nuclear magnetic resonance (NMR) experiments by 4–8 orders of magnitude. Hyperpolarized gases, unlike liquids and solids, can be more readily separated and purified from the compounds used to mediate the hyperpolarization processes. These pure hyperpolarized gases enabled many novel MRI applications including the visualization of void spaces, imaging of lung function, and remote detection. Additionally, hyperpolarized gases can be dissolved in liquids and can be used as sensitive molecular probes and reporters. This mini-review covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science.

NMR Spin-Lock Induced Crossing (SLIC) dispersion and long-lived spin states of gaseous propane at low magnetic field (0.05 T)

“…19 F MRI of perfluorinated gases such as SF 6 and C n F 2n+2 (n=1-3) 63-64 or HP noble gases, such as 3 He, 129 Xe, and others. 31, 65-66 The production of HP noble gases is relatively high cost, and it also requires sophisticated hyperpolarizer instrumentation. The imaging of both HP noble gases and 19 F via MRI additionally requires multinuclear RF coil and transmitter/receiver capabilities.…”

“…19 While any hyperpolarization technique can be used in the context of low-field NMR/MRI, less expensive and more high-throughput parahydrogen-based hyperpolarization techniques, such as parahydrogen-induced polarization (PHIP) 20-22 and signal amplification by reversible exchange (SABRE), 23-28 are naturally more suited to go hand-in-hand with an inexpensive low-field MR modality rather than the more expensive (millions of dollars) and low-throughput technique of dissolution dynamic nuclear polarization (d-DNP), 29-30 currently the leading hyperpolarization technology. 1, 31-32 It is also worth emphasizing that the maximum polarization obtainable by d-DNP depends strongly on the applied magnetic field and spin temperature (since it is a phenomenon of polarization transfer from electrons to nuclei), whereas for PHIP and SABRE the maximum polarization is independent of these parameters. Furthermore, in addition to biomedical applications, the combination of hyperpolarization and low-field detection can be also potentially useful for spectroscopic and imaging analysis of industrial-scale processes, where overpopulated pseudo-singlet spin states are conveniently created using chemical reactions involving parahydrogen.…”

Depolarization of nuclear spin polarized 129 Xe gas by dark rubidium during spin-exchange optical pumping

“…Thanks to its high solubility in tissues and wide range of chemical shifts, applications of HP 129 Xe in magnetic resonance imaging (MRI) have quickly extended from void-space imaging[3–5], to imaging of gas exchange in human lungs[6], to measurements of brain perfusion[7–9], temperature imaging[10], and imaging of metabolically active fatty tissues[11,12]. For biomedical imaging applications, 129 Xe is typically polarized via spin-exchange optical pumping (SEOP) in one of two ways: batch-mode or continuous-flow.…”

In vivo detection of cucurbit[6]uril, a hyperpolarized xenon contrast agent for a xenon magnetic resonance imaging biosensor

“…These contrast agents can be conjugated with affinity tags to create xenon MR imaging biosensors to be used as a part of a potential molecular imaging modality234. Molecular imaging allows for the molecular detection, localization, and characterization of areas of pathology within the body using medical imaging5 without the need for invasive surgical biopsies.…”