Recycling and Imaging of Nuclear Singlet Hyperpolarization
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Abstract
The
strong enhancement of NMR signals achieved by hyperpolarization
decays, at best, with a time constant of a few minutes. Here, we show
that a combination of long-lived singlet states, molecular design,
magnetic field cycling, and specific radiofrequency pulse sequences
allows repeated observation of the same batch of polarized nuclei
over a period of 30 min and more. We report a recycling protocol in
which the enhanced nuclear polarization achieved by dissolution-DNP
is observed with full intensity and then returned to singlet order.
MRI experiments may be run on a portion of the available spin polarization,
while the remaining is preserved and made available for a later use.
An analogy is drawn with a “spin bank” or “resealable
container” in which highly polarized spin order may be deposited
and retrieved