Subsecond Three-Dimensional Nitrogen-15 Magnetic Resonance Imaging Facilitated by Parahydrogen-Based Hyperpolarization

Magnetic resonance imaging (MRI) provides unique information
about
the internal structure and function of living organisms in a non-invasive
way. The use of conventional proton MRI for the observation of real-time
metabolism is hampered by the dominant signals of water and fat, which
are abundant in living organisms. Heteronuclear MRI in conjunction
with the hyperpolarization methods does not encounter this issue.
In this work, we polarized 15N nuclei of [15N1]fampridine (a drug used for the treatment of multiple
sclerosis) to the level of 4% in nuclear magnetic resonance (NMR)
experiments and 0.7% in MRI studies using spin-lock-induced crossing
combined with signal amplification by reversible exchange. Consequently,
three-dimensional 15N MRI of the hyperpolarized 15N-labeled drug was acquired in 0.1 s with a signal-to-noise ratio
of 70. In addition, the NMR signal enhancements for 15N-enriched
fampridine and fampridine with a natural abundance of 15N nuclei were compared and an explanation for their difference was
proposed.