The xenon hyperpolarization by alexandrite laser spin exchange optical pumping

Abstract

This paper shows the possibility of the use of a solid-state alexandrite laser as a radiation source for the method of spin-exchange optical pumping of noble gases (xenon, krypton). The use of dispersive optical elements in the laser cavity will allows the adjusting of the radiation wavelength exactly in the rubidium spectral absorption lines 794.7 nm and 780 nm. To obtain a hyperpolarized state of noble gases, it is necessary to excite rubidium atoms for further spin-exchange process with the noble gas nuclei. This fact will allow the increasing of the magnetic resonance imaging contrast in the field of diagnosis of respiratory organs diseases.Magnetic resonance imaging (MRI) is used to diagnose respiratory diseases, as one of the safest and most effective medical methods. Currently, MRI is based on measuring of the electromagnetic response of the hydrogen atoms nuclei, i.e. tomographic images are obtained through the use of the phenomenon of nuclear magnetic resonance (NMR). With this approach, it is difficult to visualize all human organs, such as the lungs and brain. One of the promising ways for the development of MRI is using hyperpolarized noble gases Xe, Kr, which, when inhaled by a person, increase the resolution of this diagnostic method. The nuclear polarization degree of noble gas atoms increases due to spin-exchange optical pumping (SEOP) of alkali metal vapour, which makes it possible to increase the contrast of the obtained NMR images by 5-10 times [1].This method is based on the phenomenon of spin exchange between the valence electron of an alkali metal atom in the gas phase and the nucleus of a noble gas due to collisions or the formation of Van-der-Waals interactions (Fig. 1). As the alkali metal, Rb is usually used, which has an absorption spectrum in the near infrared region. [2] Rb atoms have two transitions, D1 and D2 (Fig. 1b), when the laser is absorbed at wavelengths of 794.7 nm and 780 nm [3].To pump the Rb atomspowerful laser diodes and Ti:Sa lasers emitting at a wavelength of 794.7 nm are used. Ti:Sa lasers are capable of generating narrow-band radiation with a high pulse repetition rate, but they are large, high cost at a low average radiation power in practical applications in SEOP. Powerful laser diodes are compact source of radiation.

Organic Reaction Monitoring of a Glycine Derivative Using Signal Amplification by Reversible Exchange-Hyperpolarized Benchtop Nuclear Magnetic Resonance Spectroscopy

“…Reaction monitoring combining benchtop nuclear magnetic resonance (NMR) spectroscopy with hyperpolarization has been suggested as a potential new breakthrough in analytical technology . Hyperpolarization can be achieved using spin-state energy transfer; − well-known hyperpolarization methods include dynamic nuclear polarization (DNP), , spin-exchange optical pumping (SEOP), ,, para -hydrogen-induced polarization (PHIP), , and signal amplification by reversible exchange (SABRE). − Some strategies require extreme conditions, whereas PHIP and SABRE require relatively mild conditions in terms of temperature and magnetic field for hyperpolarization. The principal characteristic of these methods is use of para -hydrogen, which contains an antiparallel spin state and induces hyperpolarization using simple organic reactions.…”