In recent years, hyperpolarized noble gas MRI attracts attention. Spin-exchange optical pumping (SEOP) is often used for hyperpolarizing nuclear spin of noble gas. Although there are many reports on rare gas hyperpolarization devices using SEOP, most of them use high power CW lasers exceeding 10 W. Large output laser has high risk of exposure, high cost and high energy consumption. However, in SEOP, only a very small amount coincident with D1 line works and almost all other power is abandoned. Therefore, in this study, we development that Xe hyperpolarizing system using narrow linewidth Ti:Sapphire laser and demonstrated that this system can pump with lower pawer by tuning wavelength to D1 line. As a result, we show that system using narrow linewidth laser can get equally or lager signal augment ratio by 1/45 times lower irradiation power than conventional system.
We present a constructed setup for polarizing 129 Xe noble gas. Hyperpolarized 129 Xe has been obtained via spin exchange with an optically pumped rubidium vapor. Optical pumping is based on polarizing the valence electron of rubidium by the resonant absorption of a circularly polarized laser light. The magnetic field of 30 G was used for obtaining 129 Xe polarization. The apparatus for detecting polarization is a nuclear magnetic resonance spectrometer. The highest 129 Xe polarization of 54% has been obtained using 60 W circularly polarized laser light with wavelength of 794.7 nm. The measured longitudinal relaxation time of the hyperpolarized 129 Xe was 72.3 minutes.
We investigate
129Xe-Cs (
D1,D2) spin exchange optical pumping (SEOP) at high Xe densities ($~
0.12−−2.44amagat)usingnewlyavailablehigh−power(>$40 W) laser diode arrays and compare with
129Xe-Rb
D1 SEOP under similar conditions. At elevated Xe densities, the spin-exchange rate (per alkali-metal atom, ${\ensuremath{\gamma}}^{\ensuremath{'}}$) for Cs-
129Xe is $~
1.5−foldgreaterthanthatforRb−^{129}\mathrm{Xe}$. Higher spin-exchange rates and lower
129Xe spin-destruction rates for Cs-
129Xe versus Rb-
129Xe contribute to
twofold improvement in
129Xe nuclear spin polarization measured at 9.4 T---with the largest gains observed at the highest Xe densities.
A high power narrow line width (38 W, 0.09 nm full width at half maximum) external cavity diode laser is investigated for rubidium spin exchange optical pumping of X129e. This tunable photon source has a constant line width, independent of operating power or wavelength within a 1 nm tuning range. When using this laser, an increase in the X129e nuclear polarization is observed when optically pumping at a lower wavelength than the measured Rb electron D1 absorption. The exact detuning from D1 for the highest polarization is dependent upon the gas density. Furthermore, at high power and/or high Rb density, a reduction in the polarization occurs at the optimum wavelength as previously reported in spin exchange optical pumping studies of H3e which is consistent with high absorption close to the cell front face. These results are encouraging for moderate high throughput polarization of X129e in the midpressure range of (0.5–2.0 amagat).
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.
The ability to produce liter volumes of highly-spin-polarized
129Xe enables a wide range of investigations, most notably in the fields of materials science and biomedical magnetic resonance imaging. However, for nearly all polarizers built to date, both peak
129Xe polarization and the rate at which it is produced fall far below those predicted by the standard model of Rb metal vapor, spin-exchange optical pumping (SEOP). In this work we comprehensively characterized a high-volume flow-through
129Xe polarizer using three different SEOP cells with internal volumes of 100, 200, and
300cm3 and two types of optical sources: a broad-spectrum 111-W laser [full width at half maximum (FWHM) equal to 1.92 nm] and a line-narrowed 71-W laser (FWHM equal to 0.39 nm). By measuring
129Xe polarization as a function of gas flow rate, we extracted the peak polarization and polarization production rate across a wide range of laser absorption levels. Peak polarization for all cells consistently remained a factor of 2--3 times lower than predicted at all absorption levels. Moreover, although production rates increased with laser absorption, they did so much more slowly than predicted by the standard theoretical model and basic spin-exchange efficiency arguments. Underperformance was most notable in the smallest optical cells. We propose that all these systematic deviations from theory can be explained by invoking the presence of paramagnetic Rb clusters within the vapor. Cluster formation within saturated alkali-metal vapors is well established and their interaction with resonant laser light was recently shown to create plasmalike conditions. Such cluster systems cause both Rb and
129Xe depolarization, as well as excess photon scattering. These effects were incorporated into the SEOP model by assuming that clusters are activated in proportion to excited-state Rb number density and by further estimating physically reasonable values for the nanocluster-induced velocity-averaged spin-destruction cross section for Rb $(\ensuremath{\langle}{\ensuremath{\sigma}}_{\text{cluster-Rb}}v\ensuremath{\rangle}\phantom{\rule{0.16em}{0ex}}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1})$, the
129Xe relaxation cross section $(\ensuremath{\langle}{\ensuremath{\sigma}}_{\text{cluster-Xe}}v\ensuremath{\rangle}\phantom{\rule{0.16em}{0ex}}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1})$, and a non-wavelength-specific photon-scattering cross section $({\ensuremath{\sigma}}_{\mathrm{cluster}}\phantom{\rule{0.16em}{0ex}}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{2})$. The resulting modified SEOP model now closely matches experimental observations.