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% N-polarization (Theis, T.; et al. , , 1404). Hyperpolarization on N (and heteronuclei in general) may be advantageous because of the long-lived nature of the hyperpolarization on 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 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 N-hyperpolarization. The effects of parahydrogen pressure, flow rate, sample temperature, catalyst-to-substrate ratio, relaxation time (), and reversible oxygen quenching are studied on a test system of N-pyridine in methanol-. Moreover, we demonstrate the first proof-of-principle 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 N images (2 × 2 mm resolution). Importantly, this method enables hyperpolarization of molecular sites with NMR relaxation times suitable for biomedical imaging and spectroscopy.