We present a design for a spin-exchange optical pumping system to produce large quantities of highly polarized 129Xe. Low xenon concentrations in the flowing gas mixture allow the laser to maintain high Rb polarization. The large spin-exchange rate between Rb and 129Xe through the long-lived van der Waals molecules at low pressure, combined with a high flow rate, results in large production rates of hyperpolarized xenon. We report a maximum polarization of 64% achieved for a 0.3 l/h Xe flow rate, and maximum magnetization output of 6 l/h at 22% polarization. Our findings regarding the polarization dependence on temperature, nitrogen partial pressure, and gas mixture flow velocity are also reported.
We present the experimental results of generation and of detection of hyperpolarized xenon obtained by 4.7 T, 200 MHz magnetic resonance (MR) system. Xenon 129 was hyperpolarized by the spin-exchange with Rubidium pumped first by Ti:Sa laser and also by extended cavity laser system based on a high-power laser diode optimized for maximum efficiency of the optical pumping process. The application of the arrangement with semiconductor laser system is oriented medicine, especially to continuous production of hyperpolarized Xenon (HpXe) which serves as an contrast media in MR imaging systems.
Numerous designs of optical gas polarizers have been proposed, broadening possible applications of the hyperpolarized gases as contrast agents in magnetic resonance imaging. We present a home-made Xe-129 polarizer based on the spin exchange optical pumping method. The polarizer operates under 1 bar of the gas mixture (at the maximum temperature of 160 degrees C) in a high volume optical cell (5025 cm(3)). Approximately 100 cm(3) of Xe-129 polarized at 1.50 +/- 0.37% is produced in a single cycle of polarization. Operation under standard pressure imposes polarization transfer mainly via van der Waals molecules, resulting in the efficient spin exchange between rubidium and Xe-129 atoms. The design, construction and operation of the polarizer are described in details.
Recently the demand for hyperpolarized noble gases is arising to improve NMR spectroscopy resolution for imaging. Hyperpolarization of noble gases is achieved by spin- exchange with alkali metal. atoms that undergo optical pumping by circularly polarized radiation. Optical pumping is usually achieved by high power semiconductor lasers. These sources have a bandwidth very large when compared with the transition bandwidth of the optically active species. This has two serious consequences: (i) the request of high power lasers, (ii) the losses that the unemployed energy delivered to the Rb vapor can provide in the efficiency of the energy transfer. Object of our investigation will be the comparison of two experimental set ups for optical pumping of Rb vapor where pumping is given in one case by a dye laser pumped by a UV nitrogen laser built in our laboratory according to the Blumlein scheme and in the other case by a semiconductor laser. Major elements that will be discussed are (1) the role of stimulated emission of Rb vapor to increase the pumping efficiency, (2) the fate of resonant photons that are emitted during Rb decays, (3) the role of applied magnetic fields in the efficiency of pumping processes.
Here we present a $\mathrm{Rb}\text{\ensuremath{-}}^{129}\mathrm{Xe}$ spin-exchange optical pumping polarizer capable of rapid generation of large volumes of highly polarized
129Xe gas. Through modeling and measurements we maximize the
129Xe nuclear spin polarization output to enable the generation of polarized
129Xe gas imaging volumes (
300 cm3) every 5 min within a clinical setting. Our model is verified by experiment to correctly predict the optimum Rb vapor density for maximum
129Xe nuclear polarization for a flux
3.4 W/cm2 of circularly polarized Rb
D1 photons incident on an 80 cm long cylindrical optical cell. We measure a
129Xe magnetization production efficiency of ${\ensuremath{\eta}}_{\mathrm{pr}}=1.8%$, which approaches the photon efficiency limit ${\ensuremath{\eta}}_{\ensuremath{\gamma}}=3.3%$ of this system and enables the polarization of $2.72\ifmmode\times\else\texttimes\fi{}{10}^{22}$
129Xe spins per hour, corresponding to
1013 cm3 of 100% polarized
129Xe at STP. This magnetization production rate is threefold higher than the highest previously published
129Xe magnetization production rate and has enabled routine clinical lung magnetic resonance imaging (MRI) with hyperpolarized
129Xe doses available on demand at run time, as well as high-SNR
129Xe MRI of the human brain and kidneys.
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.