Ultralow-Field NMR and MRI for the Investigation of Hyperpolarization Techniques
We built a home-made ultralow-field (ULF) NMR and MRI system for the investigation of hyperpolarization techniques such as Overhauser dynamic nuclear polarization (ODNP) and parahydrogen (pH2) based hyperpolarization.
(a) Photo and schematic diagram of the coil system. For clarity, the schematic diagram shows only one of the two concave gradient coils. (b) Photo of the position of the RF coil and marker on the rat, (c) ODNP enhanced ULF, and (d) high field ex vivo MR image of a dead rat.
Ultralow-field nuclear magnetic resonance spectroscopy and magnetic resonance imaging are promising spectroscopy and imaging methods allowing for, e.g., the simultaneous detection of multiple nuclei or imaging in the vicinity of metals. To overcome the inherently low signal-to-noise ratio that usually hampers a wider application, we present an alternative approach to prepolarized ULF MR employing hyperpolarization techniques like signal amplification by reversible exchange (SABRE) or Overhauser dynamic nuclear polarization. Both techniques allow continuous hyperpolarization of 1H as well as other MR-active nuclei. For the implementation, a superconducting quantum interference device (SQUID)-based ULF MRS/MRI detection scheme was constructed. Due to the very low intrinsic noise level, SQUIDs are superior to conventional Faraday detection coils at ULFs. Additionally, the broadband characteristics of SQUIDs enable them to simultaneously detect the MR signal of different nuclei such as 13C, 19F, 15N 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.