Search

We present on the utility of in situ nuclear magnetic resonance (NMR) and near-infrared (NIR) spectroscopic techniques for automated advanced analysis of the 129Xe hyperpolarization process during spin-exchange optical pumping (SEOP). The developed software protocol, written in the MATLAB programming language, facilitates detailed characterization of hyperpolarized contrast agent production efficiency based on determination of key performance indicators, including the maximum achievable 129Xe polarization, steady-state Rb-129Xe spin-exchange and 129Xe polarization build-up rates, 129Xe spin-relaxation rates, and estimates of steady-state Rb electron polarization. Mapping the dynamics of 129Xe polarization and relaxation as a function of SEOP temperature enables systematic optimization of the batch-mode SEOP process. The automated analysis of a typical experimental data set, encompassing ∼300 raw NMR and NIR spectra combined across six different SEOP temperatures, can be performed in under 5 min on a laptop computer. The protocol is designed to be robust in operation on any batch-mode SEOP hyperpolarizer device. In particular, we demonstrate the implementation of a combination of low-cost NIR and low-frequency NMR spectrometers (∼$1,100 and ∼$300 respectively, ca. 2020) for use in the described protocols. The demonstrated methodology will aid in the characterization of NMR hyperpolarization hardware in the context of SEOP and other hyperpolarization techniques for more robust and less expensive clinical production of HP 129Xe and other contrast agents.

We report on a robust and low-cost parahydrogen generator design employing liquid nitrogen as a coolant. The core of the generator consists of catalyst-filled spiral copper tubing, which can be pressurized to 35 atm. Parahydrogen fraction >48% was obtained at 77 K with three nearly identical generators using paramagnetic hydrated iron oxide catalysts. Parahydrogen quantification was performed on the fly via benchtop NMR spectroscopy to monitor the signal from residual orthohydrogen-parahydrogen is NMR silent. This real-time quantification approach was also used to evaluate catalyst activation at up to 1.0 standard liter per minute flow rate. The reported inexpensive device can be employed for a wide range of studies employing parahydrogen as a source of nuclear spin hyperpolarization. To this end, we demonstrate the utility of this parahydrogen generator for hyperpolarization of concentrated sodium [1-13C]pyruvate, a metabolic contrast agent under investigation in numerous clinical trials. The reported pilot optimization of SABRE-SHEATH (signal amplification by reversible exchange-shield enables alignment transfer to heteronuclei) hyperpolarization yielded 13C signal enhancement of over 14,000-fold at a clinically relevant magnetic field of 1 T corresponding to approximately 1.2% 13C polarization-if near 100% parahydrogen would have been employed, the reported value would be tripled to 13C polarization of 3.5%.

[Image: see text] We report on the inexpensive ($80) custom electronics for efficient robust and fast degaussing of mu-metal shields for use in parahydrogen induced polarization experiments. The degaussing process is fully automated and can be performed in ~2 seconds resulting in residual magnetic field of

We present on the utility of in situ nuclear magnetic resonance (NMR) and near-infrared (NIR) spectroscopic techniques for automated advanced analysis of the

NMR spectroscopy and imaging (MRI) are two of the most important methods to study structure, function and dynamics from atom to organism scale. NMR approaches often suffer from an insufficient sensitivity, which, however, can be transiently boosted using hyperpolarization techniques. One of these techniques is parahydrogen-induced polarization which has been used to produce catalyst-free hyperpolarized propane gas with proton polarization that is three orders of magnitude greater than equilibrium thermal polarization at a 1.5 T field of a clinical MRI scanner. Here we show that more than 0.3 liters of hyperpolarized propane gas can be produced in 2 seconds. This production rate is more than an order of magnitude greater than that demonstrated previously, and the reported production rate is comparable to that employed for in-human MRI using HP noble gas (e.g. 129Xe) produced via Spin Exchange Optical Pumping (SEOP) hyperpolarization technique. We show that high polarization values can be retained despite the significant increase in the production rate of hyperpolarized propane. The enhanced signals of produced hyperpolarized propane gas were revealed by stopped-flow MRI visualization at 4.7 T. Achieving this high production rate enables the future use of this already compound (already approved for unlimited use in foods by the corresponding regulating agencies, e.g. FDA in the USA, and more broadly as E944 food additive) as a new inhalable contrast agent for diagnostic detection via MRI.

We present a second-generation open-source automated batch-mode 129Xe hyperpolarizer (XeUS GEN-2), designed for clinical-scale hyperpolarized (HP) 129Xe production via spin-exchange optical pumping (SEOP) in the regimes of high Xe density (0.66–2.5 atm partial pressure) and resonant photon flux (~170 W, Δλ = 0.154 nm FWHM), without the need for cryo-collection typically employed by continuous-flow hyperpolarizers. An Arduino micro-controller was used for hyperpolarizer operation. Processing open-source software was employed to program a custom graphical user interface (GUI), capable of remote automation. The Arduino Integrated Development Environment (IDE) was used to design a variety of customized automation sequences such as temperature ramping, NMR signal acquisition, and SEOP cell refilling for increased reliability. A polycarbonate 3D-printed oven equipped with a thermo-electric cooler/heater provides thermal stability for SEOP for both binary (Xe/N2) and ternary (4He-containing) SEOP cell gas mixtures. Quantitative studies of the 129Xe hyperpolarization process demonstrate that near-unity polarization can be achieved in a 0.5 L SEOP cell. For example, %PXe of 93.2 ± 2.9% is achieved at 0.66 atm Xe pressure with polarization build-up rate constant γSEOP = 0.040 ± 0.005 min−1, giving a max dose equivalent ≈ 0.11 L/h 100% hyperpolarized, 100% enriched 129Xe; %PXe of 72.6 ± 1.4% is achieved at 1.75 atm Xe pressure with γSEOP of 0.041 ± 0.001 min−1, yielding a corresponding max dose equivalent of 0.27 L/h. Quality assurance studies on this device have demonstrated the potential to refill SEOP cells hundreds of times without significant losses in performance, with average %PXe = 71.7%, (standard deviation σP = 1.52%) and mean polarization lifetime T1 = 90.5 min, (standard deviation σT = 10.3 min) over the first ~200 gas mixture refills, with sufficient performance maintained across a further ~700 refills. These findings highlight numerous technological developments and have significant translational relevance for efficient production of gaseous HP 129Xe contrast agents for use in clinical imaging and bio-sensing techniques.

We present studies of spin-exchange optical pumping (SEOP) using ternary xenon-nitrogen-helium gas mixtures at high xenon partial pressures (up to 1330 Torr partial pressure at loading, out of 2660 Torr total pressure) in a 500-mL volume SEOP cell, using two automated batch-mode clinical-scale 129Xe hyperpolarizers operating under continuous high-power (~170 W) pump laser irradiation. In this pilot study, we explore SEOP in gas mixtures with up to 45% 4He content under a wide range of experimental conditions. When an aluminum jacket cooling/heating design was employed (GEN-3 hyperpolarizer), 129Xe polarization (%PXe) of 55.9 ± 0.9% was observed with mono-exponential build-up rate γSEOP of 0.049 ± 0.001 min−1 for the 4He-rich mixture (1000 Torr Xe/900 Torr He, 100 Torr N2), compared to %PXe of 49.3 ± 3.3% at γSEOP of 0.035 ± 0.004 min−1 for the N2-rich gas mixture (1000 Torr Xe/100 Torr He, 900 Torr N2). When forced-air cooling/heating was used (GEN-2 hyperpolarizer), %PXe of 83.9 ± 2.7% was observed at γSEOP of 0.045 ± 0.005 min−1 for the 4He-rich mixture (1000 Torr Xe/900 Torr He, 100 Torr N2), compared to %PXe of 73.5 ± 1.3% at γSEOP of 0.028 ± 0.001 min−1 for the N2-rich gas mixture (1000 Torr Xe and 1000 Torr N2). Additionally, %PXe of 72.6 ± 1.4% was observed at a build-up rate γSEOP of 0.041 ± 0.003 min−1 for a super-high-density 4He-rich mixture (1330 Torr Xe/1200 Torr 4He/130 Torr N2), compared to %PXe = 56.6 ± 1.3% at a build-up rate of γSEOP of 0.034 ± 0.002 min−1 for an N2-rich mixture (1330 Torr Xe/1330 Torr N2) using forced air cooling/heating. The observed SEOP hyperpolarization performance under these conditions corresponds to %PXe improvement by a factor of 1.14 ± 0.04 at 1000 Torr Xe density and by up to a factor of 1.28 ± 0.04 at 1330 Torr Xe density at improved SEOP build-up rates by factors of 1.61 ± 0.18 and 1.21 ± 0.11 respectively. Record %PXe levels have been obtained here: 83.9 ± 2.7% at 1000 Torr Xe partial pressure and 72.6 ± 1.4% at 1330 Torr Xe partial pressure. In addition to improved thermal stability for SEOP, the use of 4He-rich gas mixtures also reduces the overall density of produced inhalable HP contrast agents; this property may be desirable for HP 129Xe inhalation by human subjects in clinical settings—especially in populations with heavily impaired lung function. The described approach should enjoy ready application in the production of inhalable 129Xe contrast agent with near-unity 129Xe nuclear spin polarization.

We present spin-exchange optical pumping (SEOP) using a third-generation (GEN-3) automated batch-mode clinical-scale 129Xe hyperpolarizer utilizing continuous high-power (∼170 W) pump laser irradia...

© 2020 Elsevier Inc. Spin-exchange optical pumping (SEOP) can enhance the NMR sensitivity of noble gases by up to five orders of magnitude at Tesla-strength magnetic fields. SEOP-generated hyperpolarised (HP) 129Xe is a promising contrast agent for lung imaging but an ongoing barrier to widespread clinical usage has been economical production of sufficient quantities with high 129Xe polarisation. Here, the ‘standard model’ of SEOP, which was previously used in the optimisation of continuous-flow 129Xe polarisers, is modified for validation against two Xe-rich stopped-flow SEOP datasets. We use this model to examine ways to increase HP Xe production efficiency in stopped-flow 129Xe polarisers and provide further insight into the underlying physics of Xe-rich stopped-flow SEOP at high laser fluxes.

We present a pilot quality assurance (QA) study of spin-exchange optical pumping (SEOP) performed on two nearly identical second-generation (GEN-2) automated batch-mode clinical-scale 129Xe hyperpolarizers, each utilizing a convective forced air oven, high-power (~170 W) continuous pump laser irradiation, and xenon-rich gas mixtures (~1.30 atm partial pressure). In one study, the repeatability of SEOP in a 1000 Torr Xe/900 Torr N2/100 Torr 4He (2000 Torr total pressure) gas mixture is evaluated over the course of ~700 gas loading cycles, with negligible decrease in performance during the first ~200 cycles, and with high 129Xe polarization levels (avg. %PXe = 71.7% with standard deviation σPXe = 1.5%), build-up rates (avg. γSEOP = 0.019 min−1 with standard deviation σγ = 0.003 min−1) and polarization lifetimes (avg. T1 = 90.5 min with standard deviation σT = 10.3 min) reported at moderate oven temperature of ~70 °C. Although the SEOP cell in this study exhibited a detectable performance decrease after 400 cycles, the cell continued to produce potentially useable HP 129Xe with %PXe = 42.3 ± 0.6% even after nearly 700 refill cycles. The possibility of “regenerating” “dormant” (i.e., not used for an extended period of time) SEOP cells using repeated temperature cycling methods to recover %PXe is also demonstrated. The quality and consistency of results show significant promise for translation to clinical-scale production of hyperpolarized 129Xe contrast agents for imaging and bio-sensing applications.

Hyperpolarized gases revolutionize functional pulmonary imaging. Hyperpolarized propane is a promising emerging contrast agent for pulmonary MRI. Unlike hyperpolarized noble gases, proton-hyperpolarized propane gas can be imaged using conventional MRI scanners with proton imaging capability. Moreover, it is non-toxic odorless anesthetic. Furthermore, propane hyperpolarization can be accomplished by pairwise addition of parahydrogen to propylene. Here, we demonstrate the feasibility of propane hyperpolarization via hydrogenation of cyclopropane with parahydrogen. 1 H propane polarization up to 2.4 % is demonstrated here using 82 % parahydrogen enrichment and heterogeneous Rh/TiO2 hydrogenation catalyst. This level of polarization is several times greater than that obtained with propylene as a precursor under the same conditions despite the fact that direct pairwise addition of parahydrogen to cyclopropane may also lead to formation of propane with NMR-invisible hyperpolarization due to magnetic equivalence of nascent parahydrogen protons in two CH3 groups. NMR-visible hyperpolarized propane demonstrated here can be formed only via a reaction pathway involving cleavage of at least one C-H bond in the reactant molecule. The resulting NMR signal enhancement of hyperpolarized propane was sufficient for 2D gradient echo MRI of ∼5.5 mL phantom with 1×1 mm2 spatial resolution and 64×64 imaging matrix despite relatively low chemical conversion of cyclopropane substrate.

We describe temperature-ramped spin-exchange optical pumping (TR-SEOP) in an automated high-throughput batch-mode (129)Xe hyperpolarizer utilizing three key temperature regimes: (i) "hot"-where the (129)Xe hyperpolarization rate is maximal, (ii) "warm"-where the (129)Xe hyperpolarization approaches unity, and (iii) "cool"-where hyperpolarized (129)Xe gas is transferred into a Tedlar bag with low Rb content (5 ng per ∼1 L dose) suitable for human imaging applications. Unlike with the conventional approach of batch-mode SEOP, here all three temperature regimes may be operated under continuous high-power (170 W) laser irradiation, and hyperpolarized (129)Xe gas is delivered without the need for a cryocollection step. The variable-temperature approach increased the SEOP rate by more than 2-fold compared to the constant-temperature polarization rate (e.g., giving effective values for the exponential buildup constant γSEOP of 62.5 ± 3.7 × 10(-3) min(-1) vs 29.9 ± 1.2 × 10(-3) min(-1)) while achieving nearly the same maximum %PXe value (88.0 ± 0.8% vs 90.1% ± 0.8%, for a 500 Torr (67 kPa) Xe cell loading-corresponding to nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI) enhancements of ∼3.1 × 10(5) and ∼2.32 × 10(8) at the relevant fields for clinical imaging and HP (129)Xe production of 3 T and 4 mT, respectively); moreover, the intercycle "dead" time was also significantly decreased. The higher-throughput TR-SEOP approach can be implemented without sacrificing the level of (129)Xe hyperpolarization or the experimental stability for automation-making this approach beneficial for improving the overall (129)Xe production rate in clinical settings.

Here we provide a full report on the construction, components, and capabilities of our consortium’s “open-source” large-scale (~ 1 L/h) 129Xe hyperpolarizer for clinical, pre-clinical, and materials NMR/MRI (Nikolaou et al., Proc. Natl. Acad. Sci. USA, 110, 14150 (2013)). The ‘hyperpolarizer’ is automated and built mostly of off-the-shelf components; moreover, it is designed to be cost-effective and installed in both research laboratories and clinical settings with materials costing less than $125,000. The device runs in the xenon-rich regime (up to 1800 Torr Xe in 0.5 L) in either stopped-flow or single-batch mode—making cryo-collection of the hyperpolarized gas unnecessary for many applications. In-cell 129Xe nuclear spin polarization values of ~ 30%–90% have been measured for Xe loadings of ~ 300–1600 Torr. Typical 129Xe polarization build-up and T1 relaxation time constants were ~ 8.5 min and ~ 1.9 h respectively under our spin-exchange optical pumping conditions; such ratios, combined with near-unity Rb electron spin polarizations enabled by the high resonant laser power (up to ~ 200 W), permit such high PXe values to be achieved despite the high in-cell Xe densities. Importantly, most of the polarization is maintained during efficient HP gas transfer to other containers, and ultra-long 129Xe relaxation times (up to nearly 6 h) were observed in Tedlar bags following transport to a clinical 3 T scanner for MR spectroscopy and imaging as a prelude to in vivo experiments. The device has received FDA IND approval for a clinical study of chronic obstructive pulmonary disease subjects. The primary focus of this paper is on the technical/engineering development of the polarizer, with the explicit goals of facilitating the adaptation of design features and operative modes into other laboratories, and of spurring the further advancement of HP-gas MR applications in biomedicine.

We present a systematic, multiparameter study of Rb/(129)Xe spin-exchange optical pumping (SEOP) in the regimes of high xenon pressure and photon flux using a 3D-printed, clinical-scale stopped-flow hyperpolarizer. In situ NMR detection was used to study the dynamics of (129)Xe polarization as a function of SEOP-cell operating temperature, photon flux, and xenon partial pressure to maximize (129)Xe polarization (PXe). PXe values of 95 ± 9%, 73 ± 4%, 60 ± 2%, 41 ± 1%, and 31 ± 1% at 275, 515, 1000, 1500, and 2000 Torr Xe partial pressure were achieved. These PXe polarization values were separately validated by ejecting the hyperpolarized (129)Xe gas and performing low-field MRI at 47.5 mT. It is shown that PXe in this high-pressure regime can be increased beyond already record levels with higher photon flux and better SEOP thermal management, as well as optimization of the polarization dynamics, pointing the way to further improvements in hyperpolarized (129)Xe production efficiency.

Nuclear spin polarization can be significantly increased through the process of hyperpolarization, leading to an increase in the sensitivity of nuclear magnetic resonance (NMR) experiments by 4-8 orders of magnitude. Hyperpolarized gases, unlike liquids and solids, can be more readily separated and purified from the compounds used to mediate the hyperpolarization processes. These pure hyperpolarized gases enabled many novel MRI applications including the visualization of void spaces, imaging of lung function, and remote detection. Additionally, hyperpolarized gases can be dissolved in liquids and can be used as sensitive molecular probes and reporters. This mini-review covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science.

This chapter introduces the physical principles underlying hyperpolarized (HP) gas magnetic resonance. The properties of such HP gases, including spin I ≥1/2 noble gas isotopes and low molecular-mass gases like propane, are introduced in the context of biomedical applications. Of particular interest are mechanisms of relaxation and contrast, and the ramifications of using HP gases in magnetic resonance imaging studies. The primary technologies for producing such HP gases are also introduced and described, including spin-exchange optical pumping (SEOP), metastability-exchange optical pumping (MEOP), “brute-force” polarization (BFP), dynamic nuclear polarization (DNP), and parahydrogen-induced polarization (PHIP). The advantages, limitations, and outlooks for such approaches are discussed.

Next-generation laser diode arrays with integrated ‘on-chip’ volume holographic gratings can provide high power with spectrally narrowed output that can be tuned about the rubidium D1 line—without causing significant changes to the laser’s flux or spectral profile. These properties were exploited to independently evaluate the effects of varying the laser centroid wavelength and power on batch-mode Rb/129Xe spin-exchange optical pumping (SEOP) as functions of xenon partial pressure and cell temperature. Locally optimized SEOP was often achieved with the laser tuned to either the red or blue side of the Rb D1 line; global optimization of SEOP was observed at lower cell temperatures and followed the D1 absorption profile, which was asymmetrically broadened and red-shifted from the nominal wavelength. The complex dependence of the optimal wavelength for laser excitation on the cell temperature and Xe density appears to result from an interplay between cell illumination and the Rb/129Xe spin-exchange rate, as well as [Xe]cell-dependent changes to the Rb absorption lineshape that are in qualitative agreement with expectations based on previous work [Romalis et al., Phys. Rev. A, 56:4569–4578, (1997)], but significantly greater in magnitude. These next-generation lasers provide a ∼2–3-fold improvement in 129Xe polarization compared to conventional broadband lasers.

The 129 Xe nuclear spin polarization ( P Xe ) that can be achieved via spin-exchange optical pumping (SEOP) is typically limited at high in-cell xenon densities ([Xe] cell ), due primarily to corresponding reductions in the alkali metal electron spin polarization (e.g. P Rb ) caused by increased non-spin-conserving Rb–Xe collisions. While demonstrating the utility of volume holographic grating (VHG)-narrowed lasers for Rb/ 129 Xe SEOP, we recently reported [P. Nikolaou et al., JMR 197 (2009) 249] an anomalous dependence of the observed P Xe on the in-cell xenon partial pressure ( p Xe ), wherein P Xe values were abnormally low at decreased p Xe , peaked at moderate p Xe (∼300 torr), and remained surprisingly elevated at relatively high p Xe values (>1000 torr). Using in situ low-field 129 Xe NMR, it is shown that the above effects result from an unexpected, inverse relationship between the xenon partial pressure and the optimal cell temperature ( T OPT ) for Rb/ 129 Xe SEOP. This interdependence appears to result directly from changes in the efficiency of one or more components of the Rb/ 129 Xe SEOP process, and can be exploited to achieve improved P Xe with relatively high xenon densities measured at high field (including averaged P Xe values of ∼52%, ∼31%, ∼22%, and ∼11% at 50, 300, 500, and 2000 torr, respectively).

Visible emission from Rb optical pumping cells was characterized under a range of conditions relevant to the production of laser-polarized xenon (including temperature, partial pressures, and D 1 -resonant 795 nm laser power). Bright 421 nm (6P → 5S) emission was consistent with energy-pooling processes of the type: Rb ∗ (5P 1/2 ) + Rb ∗ (5P 1/2,3/2 ) → Rb ∗ (6P 1/2,3/2 ) + Rb(5S 1/2 ), with processes transiting through 5D states likely contributing at higher temperatures/lower N 2 partial pressures. Under such conditions a number of Rb lines may be observed, indicating population of Rb states to ⩾9D (∼31 822 cm −1 ). Such energies exceed those required for efficient production of laser-induced plasma.

The interactions between xenon and DMPC/DHPC bicelles ( q = 3.5%, 7.5% w/v) were studied via 2 H, 129 Xe, 131 Xe, and optically enhanced 129 Xe NMR. The chemical shifts, linewidths, and quadrupolar couplings of the xenon/bicelle NMR signals were correlated with different regions of the bicellar phase diagram. The addition of xenon ( 129 Xe T 1 values of ∼120 s, long enough to permit a variety of planned experiments.

Over the last two-plus decades, hyperpolarized (HP) 129Xe has been exploited for a wide range of magnetic resonance applications. HP 129Xe is usually created by spin-exchange optical pumping (SEOP). This chapter reviews efforts in our laboratories and those of our collaborators to explore HP 129Xe generation via SEOP in the demanding regimes of high xenon densities and resonant laser powers. Of particular importance is the technical development of high-power frequency-narrowed laser sources which, combined with fundamental studies, have enabled high 129Xe polarizations to be achieved at relatively high Xe densities under conditions of stopped-flow production. Efforts exploring the interplay between gas mixture, laser power, laser wavelength, and cell temperature in determining 129Xe polarization efficiency have led to the development of automated, clinical-scale 129Xe “hyperpolarizers” capable of generating significant quantities of 129Xe with near-unity polarization and without the need for cryogenic collection—including an “open-source” design approved and demonstrated for human use, and an improved design centered around a 3-D printed oven. Another area of interest is how the high resonant laser energy is absorbed, thermalized, and dissipated during SEOP. The potential advantages of using Cs instead of—or in addition to—Rb as the alkali metal are also explored.

Recent developments in NMR hyperpolarization have enabled a wide array of new in vivo molecular imaging modalities, ranging from functional imaging of the lungs to metabolic imaging of cancer. This Concept article explores selected advances in methods for the preparation and use of hyperpolarized contrast agents, many of which are already at or near the phase of their clinical validation in patients.

Three-dimensional printing with high-temperature plastic is used to enable spin exchange optical pumping (SEOP) and hyperpolarization of xenon-129 gas. The use of 3D printed structures increases the simplicity of integration of the following key components with a variable temperature SEOP probe: (i) in situ NMR circuit operating at 84 kHz (Larmor frequencies of (129)Xe and (1)H nuclear spins), (ii)

The exquisite NMR spectral sensitivity and negligible reactivity of hyperpolarized xenon-129 (HP(129)Xe) make it attractive for a number of magnetic resonance applications; moreover, HP(129)Xe embodies an alternative to rare and nonrenewable (3)He. However, the ability to reliably and inexpensively produce large quantities of HP(129)Xe with sufficiently high (129)Xe nuclear spin polarization (P(Xe)) remains a significant challenge--particularly at high Xe densities. We present results from our "open-source" large-scale (∼1 L/h) (129)Xe polarizer for clinical, preclinical, and materials NMR and MRI research. Automated and composed mostly of off-the-shelf components, this "hyperpolarizer" is designed to be readily implementable in other laboratories. The device runs with high resonant photon flux (up to 200 W at the Rb D1 line) in the xenon-rich regime (up to 1,800 torr Xe in 500 cc) in either single-batch or stopped-flow mode, negating in part the usual requirement of Xe cryocollection. Excellent agreement is observed among four independent methods used to measure spin polarization. In-cell P(Xe) values of ∼90%, ∼57%, ∼50%, and ∼30% have been measured for Xe loadings of ∼300, ∼500, ∼760, and ∼1,570 torr, respectively. P(Xe) values of ∼41% and ∼28% (with ∼760 and ∼1,545 torr Xe loadings) have been measured after transfer to Tedlar bags and transport to a clinical 3 T scanner for MR imaging, including demonstration of lung MRI with a healthy human subject. Long "in-bag" (129)Xe polarization decay times have been measured (T1 ∼38 min and ∼5.9 h at ∼1.5 mT and 3 T, respectively)--more than sufficient for a variety of applications.

Volume holographic gratings (VHGs) can be exploited to narrow the spectral output of high-power laser-diode arrays (LDAs) by nearly an order of magnitude, permitting more efficient generation of laser-polarized noble gases for various applications. A approximately 3-fold improvement in (129)Xe nuclear spin polarization, P(Xe), (compared to a conventional LDA) was achieved with the VHG-LDA's center wavelength tuned to a wing of the Rb D(1) line. Additionally, an anomalous dependence of P(Xe) on the xenon density within the OP cell is reported-including high P(Xe) values (10%) at high xenon partial pressures (approximately 1000 torr).