Abstract
Hyperpolarized magnetic resonance spectroscopy (HP MRS) using dynamic nuclear polarization (DNP) is a technique that has greatly enhanced the sensitivity of detecting 13C nuclei. However, the HP MRS polarization decays in the liquid state according to the spin-lattice relaxation time (T1) of the nucleus. Sampling of the signal also destroys polarization, resulting in a limited temporal ability to observe biologically interesting reactions. In this study, we demonstrate that sampling hyperpolarized signals using a permanent magnet at 1 Tesla (1T) is a simple and cost-effective method to increase T1s without sacrificing signal-to-noise. Biologically-relevant information may be obtained with a permanent magnet using enzyme solutions and in whole cells. Of significance, our findings indicate that changes in pyruvate metabolism can also be quantified in a xenograft model at this field strength.
Highlights
Nuclear magnetic resonance (NMR) spectroscopy of biologically relevant nuclei, aside from protons, has long been limited by the lack of sensitivity
HP MRI has been informative in many fields including tumor metabolism[27], cardiac biology[28] as well as inflammation[29]
In a literature search on Pubmed with the terms ‘hyperpolarized’ and ‘dynamic nuclear polarization’, we assessed 185 publications dating back to 2002 and uncovered no instances of HP experiments performed on permanent magnets with the lowest field strength recorded was a 2.4 T super-conducting, small animal imaging system[30]
Summary
Nuclear magnetic resonance (NMR) spectroscopy of biologically relevant nuclei, aside from protons, has long been limited by the lack of sensitivity. One approach involves converting polarization to a nuclear singlet-state order that can be stored and accessed This can be accomplished through field cycling, continuous irradiation or chemical modification but none of these methods are compatible with biologically relevant imaging systems[6]. The singlet-state can only be accessed with a limited class of chemical structures and a more practical method of increasing the lifetime of polarization is by substituting exchangeable protons with deuterium (2H) This has been demonstrated with a number of different metabolites[8,9,10], with reasonable increases in T1, this method might be prohibitive due to the high costs involved in synthesizing deuterated substrates, limiting for screening large libraries of non-labeled compounds, as well as the potential for an isotope effect slowing biochemical kinetics[11]. To the best of our knowledge, the use of a permanent, 1T spectrometer has yet to be demonstrated with hyperpolarized MR
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