Radio-Frequency Sweeps at {\mu}T Fields for Parahydrogen-Induced Polarization of Biomolecules

TL;DR

This paper presents a robust method using adiabatic RF sweeps at microtesla fields to transfer parahydrogen-induced polarization to 13C in biomolecules, significantly enhancing MRI signals for metabolic imaging.

Contribution

The authors introduce a new, easily implementable RF sweep technique for polarization transfer at microtesla fields, improving polarization levels and enabling site-selective deuteration to boost efficiency.

Findings

Achieved over 60% polarization in some molecules.

Demonstrated applicability to metabolic imaging compounds.

Enhanced polarization transfer efficiency by avoiding relaxation from quadrupolar nuclei.

Abstract

Magnetic resonance imaging of $^{13}$C-labeled metabolites enhanced by parahydrogen-induced polarization (PHIP) can enable real-time monitoring of processes within the body. We introduce a robust, easily implementable technique for transferring parahydrogen-derived singlet order into 13C magnetization using adiabatic radio-frequency sweeps at $\mu$T fields. We experimentally demonstrate the applicability of this technique to several molecules, including some molecules relevant for metabolic imaging, where we show significant improvements in the achievable polarization, in some cases reaching above 60%. Furthermore, we introduce a site-selective deuteration scheme, where deuterium is included in the coupling network of a pyruvate ester to enhance the efficiency of the polarization transfer. These improvements are enabled by the fact that the transfer protocol avoids relaxation induced by strongly coupled quadrupolar nuclei.