N Hyperpolarization by Reversible Exchange Using SABRE-SHEATH.
NMR signal amplification by reversible exchange (SABRE) is a NMR hyperpolarization technique that enables nuclear spin polarization enhancement of molecules via concurrent chemical exchange of a target substrate and parahydrogen (the source of spin order) on an iridium catalyst. Recently, we demonstrated that conducting SABRE in microtesla fields provided by a magnetic shield enables up to 10% 15
N-polarization (Theis, T.; et al. J. Am. Chem. Soc.
, 1404). Hyperpolarization on 15
N (and heteronuclei in general) may be advantageous because of the long-lived nature of the hyperpolarization on 15
N relative to the short-lived hyperpolarization of protons conventionally hyperpolarized by SABRE, in addition to wider chemical shift dispersion and absence of background signal. Here we show that these unprecedented polarization levels enable 15
N magnetic resonance imaging. We also present a theoretical model for the hyperpolarization transfer to heteronuclei, and detail key parameters that should be optimized for efficient 15
N-hyperpolarization. The effects of parahydrogen pressure, flow rate, sample temperature, catalyst-to-substrate ratio, relaxation time (T
), and reversible oxygen quenching are studied on a test system of 15
N-pyridine in methanol-d
. Moreover, we demonstrate the first proof-of-principle 13
C-hyperpolarization using this method. This simple hyperpolarization scheme only requires access to parahydrogen and a magnetic shield, and it provides large enough signal gains to enable one of the first 15
N images (2 × 2 mm2
resolution). Importantly, this method enables hyperpolarization of molecular sites with NMR T
relaxation times suitable for biomedical imaging and spectroscopy.
Truong, ML; Theis, T; Coffey, AM; Shchepin, RV; Waddell, KW; Shi, F; Goodson, BM; Warren, WS; Chekmenev, EY
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