hyperpolarisoinnin

Hyperpolarisation is a technique used in nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) to artificially increase the signal intensity of certain atomic nuclei. In a typical NMR or MRI experiment, the nuclei within a sample are aligned by a strong magnetic field to a state of thermal equilibrium, where only a small excess of nuclei are aligned with the field. This small excess is responsible for the NMR/MRI signal. Hyperpolarisation significantly enhances this excess population, leading to a signal that can be thousands or even tens of thousands of times stronger than that obtained under thermal equilibrium conditions.

There are several methods for achieving hyperpolarisation, including spin exchange optical pumping (SEOP), dynamic nuclear polarisation (DNP), and parahydrogen-induced polarisation (PHIP). SEOP typically involves using lasers to polarise electron spins in alkali metal vapour, which are then transferred to the nuclear spins of noble gases like xenon or helium. DNP relies on transferring polarisation from unpaired electrons in a paramagnetic substance to nearby nuclear spins, often at very low temperatures. PHIP utilises the unique spin properties of parahydrogen, an isomer of hydrogen gas, to polarise molecules that react with it.

The increased signal strength offered by hyperpolarisation has significant implications for various fields. In medical imaging, it allows for faster scans and the visualisation of previously undetectable metabolic processes or rare cell populations. In chemistry, it can enable the study of transient species, reaction mechanisms, and molecules present at very low concentrations. The development of hyperpolarisation techniques has opened new avenues for research and diagnostics, pushing the boundaries of what can be observed with NMR and MRI.