Single-Shot MRI in parahydrogen hyperpolarized samples

Abstract

The site-specific signal enhancement provided by parahydrogen induced polarization (PHIP) may be combined with magnetic resonance imaging (MRI) to study chemical and biomolecular processes. However, imaging of hydrogen nuclei (${}^1$H) is hampered by background signals arising from the presence of thermally polarized nuclei. Additionally, fast imaging sequences are commonly based on multiple radio-frequency pulses, where the signals resulting from PHIP oscillate due to the evolution with a $J$-coupling Hamiltonian. In this article, an innovative imaging scheme for single-scan MRI is presented that effectively detects hyperpolarized components while simultaneously canceling out thermal contributions. This method is based on the quenching of inherent oscillations of PHIP-originated signals due to $J$-couplings during the multipulse sequence and the suppression of thermal signals by spin dynamics and a tailored restructuring of the $k$-space. A series of numerical simulations on specific two- and three-spin systems serve to support the feasibility of the approach. Furthermore, this theoretical study demonstrates the potential of combining hyperpolarization and long-lived states (PHIP and LLS) in the selected molecules, which could be seen as a preliminary step towards the development of fast imaging techniques, for example in the field of biomolecular research.