Dipolar order mediated &amp;lt;sup&amp;gt;1&amp;lt;/sup&amp;gt;H → &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C cross-polarization for dissolution-dynamic nuclear polarization

Stuart J Elliott,Quentin Chappuis,Morgan Ceillier,Samuel F Cousin,Sami Jannin,Aurélien Bornet,Olivier Cala

doi:10.5194/mr-1-89-2020

Abstract

Abstract. Magnetic resonance imaging and spectroscopy often suffer from a low intrinsic sensitivity, which can in some cases be circumvented by the use of hyperpolarization techniques. Dissolution-dynamic nuclear polarization offers a way of hyperpolarizing 13C spins in small molecules, enhancing their sensitivity by up to 4 orders of magnitude. This is usually performed by direct 13C polarization, which is straightforward but often takes more than an hour. Alternatively, indirect 1H polarization followed by 1H→13C polarization transfer can be implemented, which is more efficient and faster but is technically very challenging and hardly implemented in practice. Here we propose to remove the main roadblocks of the 1H→13C polarization transfer process by using alternative schemes with the following: (i) less rf (radiofrequency) power; (ii) less overall rf energy; (iii) simple rf-pulse shapes; and (iv) no synchronized 1H and 13C rf irradiation. An experimental demonstration of such a simple 1H→13C polarization transfer technique is presented for the case of [1-13C]sodium acetate, and is compared with the most sophisticated cross-polarization schemes. A polarization transfer efficiency of ∼0.43 with respect to cross-polarization was realized, which resulted in a 13C polarization of ∼8.7 % after ∼10 min of microwave irradiation and a single polarization transfer step.

Highlights

Traditional magnetic resonance imaging (MRI) and spectroscopy (MRS) experiments usually suffer from low sensitivity
It is important to note that the maximum is identical whether the nuclear magnetic resonance (NMR) signal is observed on the 1H rf channel by using variant no. 1a or on the 13C rf channel by using variant no. 1b, and that more generally the two traces have the same shape and optimum
This shows that 13C transverse magnetization from dCP is proportional to the 1H–1H dipolar order initially prepared

Summary

Introduction

Traditional magnetic resonance imaging (MRI) and spectroscopy (MRS) experiments usually suffer from low sensitivity. Hyperpolarization techniques including dissolutiondynamic nuclear polarization (dDNP) can be used to highly polarize a large variety of chemical systems and enhance nuclear magnetic resonance (NMR) signals by several orders of magnitude (Ardenkjær-Larsen et al, 2003). The use and optimization of cross-polarization (CP) under dDNP conditions (typically at temperatures of about 1.2–1.6 K in superfluid helium) provides a way to substantially boost 13C polarizations and enhance build-up rates 1/τDNP(13C) (by a factor of up to 40) (Hartmann and Hahn, 1962; Pines et al, 1972; Perez Linde, 2009; Jannin et al, 2011; Bornet et al, 2012, 2013; Batel et al, 2012; Vuichoud et al, 2016; Cavaillès et al, 2018). The technique requires intense B1 matching (typically > 15 kHz) of simultaneous 1H

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Discussion

Conclusion