Abstract
Hyperpolarization techniques can enormously enhance the NMR signal thus allowing the exploitation of hyperpolarized substrates for in-vivo MRI applications. The short lifetime of hyperpolarized spin order poses significant limitations in such applications. Spin order storage can be prolonged through the use of long-lived spin states. Additionally, the storage of spin polarization–either in the form of longitudinal or singlet order–can be prolonged in low viscosity solutions. Here, we report the use of low viscosity liquid-CO2 solutions to store nuclear spin polarization in the form of longitudinal and singlet order for extended periods. Our results demonstrate that this storage time can be considerably sustained in liquid-CO2 solutions in comparison to other low viscosity solvents, opening up the possibility of new, exciting storage experiments in the future.
Highlights
Molecules that contain an “isolated” spin-1/2 pair of nuclei, offer the possibility to prepare a form of spin order, namely, singlet spin order (Carravetta and Levitt, 2004; Carravetta et al, 2004; Pileio, 2020) with the fundamental property of being long-lived
We present a thorough investigation of the lifetime of longitudinal and singlet spin order in liquid-CO2 solutions as compared with the same values measured in more conventional organic solvents
The motivation behind this work was the concept that longitudinal and singlet order lifetimes could be extended in low viscosity compressed gases in comparison to solvents which are liquid at ordinary pressures and temperatures
Summary
Molecules that contain an “isolated” spin-1/2 pair of nuclei, offer the possibility to prepare a form of spin order, namely, singlet spin order (Carravetta and Levitt, 2004; Carravetta et al, 2004; Pileio, 2020) with the fundamental property of being long-lived This is due to the fact that singlet spin order decays at a much slower rate than the longitudinal spin order conventionally used in most NMR experiments. The possibility to preserve hyperpolarization for hour-long periods would allow delocalisation of the point-of-production (the hyperpolarization equipment) from the point-of-use (the NMR/MRI machine) This presents many advantages but perhaps the most important is that the point-of-use does not necessarily need to be equipped with hyperpolarizer instrumentation and have specially trained personnel (in the case of dissolution-DNP this is very costly)
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