Towards a unified picture of polarization transfer -- pulsed DNP and chemically equivalent PHIP

Nuclear spin hyperpolarization techniques, such as dynamic nuclear polarization (DNP) and parahydrogen-induced polarization (PHIP), have revolutionized nuclear magnetic resonance and magnetic resonance imaging. In these methods, a readily available source of high spin order, either electron spins in DNP or singlet states in hydrogen for PHIP, is brought into close proximity with nuclear spin targets, enabling efficient transfer of spin order under external quantum control. Despite vast disparities in energy scales and interaction mechanisms between electron spins in DNP and nuclear singlet states in PHIP, a pseudo-spin formalism allows us to establish an intriguing equivalence. As a result, the important low-field polarization transfer regime of PHIP can be mapped onto an analogous system equivalent to pulsed-DNP. This establishes a correspondence between key polarization transfer sequences in PHIP and DNP, facilitating the transfer of sequence development concepts. This promises fresh insights and significant cross-pollination between DNP and PHIP polarization sequence developers.Comment: 11+5 pages, 5 figure

Optically induced dynamic nuclear spin polarisation in diamond

The sensitivity of Magnetic Resonance Imaging (MRI) depends strongly on nuclear spin polarisation and, motivated by this observation, dynamical nuclear spin polarisation has recently been applied to enhance MRI protocols (Kurhanewicz, J., et al., Neoplasia 13, 81 (2011)). Nuclear spins associated with the 13 C carbon isotope (nuclear spin I = 1/2) in diamond possess uniquely long spin lattice relaxation times (Reynhardt, E.C. and G.L. High, Prog. in Nuc. Mag. Res. Sp. 38, 37 (2011)) If they are present in diamond nanocrystals, especially when strongly polarised, they form a promising contrast agent for MRI. Current schemes for achieving nuclear polarisation, however, require cryogenic temperatures. Here we demonstrate an efficient scheme that realises optically induced 13 C nuclear spin hyperpolarisation in diamond at room temperature and low ambient magnetic field. Optical pumping of a Nitrogen-Vacancy (NV) centre creates a continuously renewable electron spin polarisation which can be transferred to surrounding 13 C nuclear spins. Importantly for future applications we also realise polarisation protocols that are robust against an unknown misalignment between magnetic field and crystal axis.Comment: This is the revision submitted to NJ

Over 20% 13C Hyperpolarization for Pyruvate Using Deuteration and Rapid SLIC-SABRE in Mictrotesla Fields

Carbon-13 hyperpolarized pyruvate is about to become the next-generation contrast agent for molecular magnetic resonance imaging of cancer and other diseases. Here, efficient and rapid pyruvate hyperpolarization is achieved via Signal Amplification by Reversible Exchange (SABRE) with parahydrogen through synergistic use of substrate deuteration, alternating, and static microtesla magnetic fields. Up to 22% and 6% long-lasting 13C polarization (T1=3.7±0.25min and T1=1.7±0.1min) is demonstrated for the C1 and C2 nuclear sites, respectively. The remarkable polarization levels become possible due to favorable relaxation dynamics at the microtesla fields. The ultra-long polarization lifetimes will be conducive to yielding high polarization after purification, quality assurance, and injection of the hyperpolarized molecular imaging probes. These results pave the way to future in vivo translation of carbon-13 hyperpolarized molecular imaging probes prepared by this approach

Radio-Frequency Sweeps at {\mu}T Fields for Parahydrogen-Induced Polarization of Biomolecules

Magnetic resonance imaging of $^{13}$C-labeled metabolites enhanced by parahydrogen-induced polarization (PHIP) can enable real-time monitoring of processes within the body. We introduce a robust, easily implementable technique for transferring parahydrogen-derived singlet order into 13C magnetization using adiabatic radio-frequency sweeps at $\mu$T fields. We experimentally demonstrate the applicability of this technique to several molecules, including some molecules relevant for metabolic imaging, where we show significant improvements in the achievable polarization, in some cases reaching above 60%. Furthermore, we introduce a site-selective deuteration scheme, where deuterium is included in the coupling network of a pyruvate ester to enhance the efficiency of the polarization transfer. These improvements are enabled by the fact that the transfer protocol avoids relaxation induced by strongly coupled quadrupolar nuclei