Toward Biocompatible Nuclear Hyperpolarization Using Signal Amplification by Reversible Exchange: Quantitative <i>in Situ</i> Spectroscopy and High-Field Imaging

Abstract

Signal amplification by reversible exchange (SABRE) of a substrate and parahydrogen at a catalytic center promises to overcome the inherent insensitivity of magnetic resonance. In order to apply the new approach to biomedical applications, there is a need to develop experimental equipment, in situ quantification methods, and a biocompatible solvent. We present results detailing a low-field SABRE polarizer which provides well-controlled experimental conditions, defined spins manipulations, and which allows in situ detection of thermally polarized and hyperpolarized samples. We introduce a method for absolute quantification of hyperpolarization yield in situ by means of a thermally polarized reference. A maximum signal-to-noise ratio of ∼10(3) for 148 μmol of substance, a signal enhancement of 10(6) with respect to polarization transfer field of SABRE, or an absolute (1)H-polarization level of ≈10(-2) is achieved. In an important step toward biomedical application, we demonstrate (1)H in situ NMR as well as (1)H and (13)C high-field MRI using hyperpolarized pyridine (d3) and (13)C nicotinamide in pure and 11% ethanol in aqueous solution. Further increase of hyperpolarization yield, implications of in situ detection, and in vivo application are discussed.