hyperpolariseringsfaktor

A hyperpolariser is a device designed to produce hyperpolarised nuclear spin states in target molecules, enabling large enhancements of magnetic resonance signals for experiments in chemistry, physics, and medical imaging. Hyperpolarisation refers to population distributions of nuclear spins that deviate far from thermal equilibrium, yielding signal gains of manyfold over conventional polarisation.

There are several principal methods for achieving hyperpolarisation. Dynamic nuclear polarisation uses cryogenic temperatures and strong magnetic fields to align electron spins in stable radicals and transfers this alignment to nuclei with microwave irradiation. Spin-exchange optical pumping uses laser light to polarise an alkali metal vapour, which transfers angular momentum to surrounding nuclei, often noble gases such as xenon-129 or helium-3. Para-hydrogen induced polarization relies on chemical reactions that transfer the spin order of para-hydrogen into target molecules.

Hyperpolarised agents are used to enhance magnetic resonance imaging and spectroscopy. In vivo, hyperpolarised xenon or helium enables high-contrast lung imaging; hyperpolarised carbon-13 compounds allow metabolic imaging, real-time monitoring of biochemical pathways, and drug development. The hyperpolarised state decays due to spin-lattice relaxation, with lifetimes that vary by nucleus and environment, requiring rapid transport from the polarisation site to the measurement system and specialized hardware.

Limitations and challenges include the need for cryogenics or high-power lasers, short-lived polarization for many nuclei, and the complexity and cost of equipment. Research continues to extend lifetimes, improve polarisation levels, and develop new agents for clinical and fundamental applications.