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Abstract:
Introduction
Ultralow-field (ULF) nuclear magnetic resonance (NMR) is a promising spectroscopy method allowing for, e.g., the simultaneous detection of multiple nuclei. To overcome the low signal-to-noise ratio that usually hampers a wider application, we present an alternative approach to prepolarized ULF NMR employing hyperpolarization techniques like signal amplification by reversible exchange (SABRE) or Overhauser dynamic nuclear polarization (ODNP). Both techniques allow continuous hyperpolarization of 1H as well as other MR-active nuclei.
Methods
To be able to measure 1H and 19F simultaneously, a superconducting quantum interference device (SQUID)-based ULF NMR/MRI detection unit was constructed (see fig. 1). Due to the very low intrinsic noise level, SQUIDs are superior to conventional Faraday detection coils at ultralow-fields. Additionally, the broad band characteristics of SQUIDs enable them to simultaneously detect the MR signal of different nuclei such as 13C, 19F or 1H. Since SQUIDs detect the MR signal directly, they are an ideal tool for a quantitative investigation of hyperpolarization techniques such as SABRE or ODNP.
Results/Discussion
Using SABRE we successfully hyperpolarized fluorinated pyridine derivatives and quantitatively characterized the dependency of the magnetization transfer reaction from parahydrogen, which bonds to an iridium complex as well as to the 1H and 19F nuclei of an exchangeable ligand, as a function of hyperpolarization time and magnetic field strength [1]. Spectra (see fig. 2) and images of the samples were acquired.
With ODNP we were able to measure the coupling constant of solutions containing free radicals. Enhancement factors of over 100 were reached in in situ experiments. First proof-of-principle ex vivo images of rats using ODNP enhanced, SQUID based ULF-MRI have been acquired successfully.
Conclusions
We successfully built a SQUID-based ULF NMR/MRI system to quantitatively investigate the hyperpolarization techniques SABRE and ODNP.
