Comparative study of in situ N2 rotational Raman spectroscopy methods for probing energy thermalisation processes during spin-exchange optical pumping

Newton, Hayley; Walkup, Laura L.; Whiting, Nicholas; West, L.; Carriere, James; Havermeyer, Frank; Ho, L. T.; Morris, Peter G.; Goodson, Boyd M.; Barlow, Michael J.

doi:10.1007/s00340-013-5588-x

Cited by 10 publications

(12 citation statements)

References 21 publications

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“…The maximum expected xenon polarization should be on the order of 44% for these parameters, whereas the maximum final xenon polarization obtained experimentally was only 25%. While slight mismatches between the calculated and observed temperature for maximum 129 Xe polarization can be easily explained by uneven laser light heating of the gas inside the optical cell, as previously reported in the literature [35–38], the decrease in polarization observed at higher temperatures is clearly faster than what is predicted by the standard model.…”

Section: Resultssupporting

confidence: 73%

Depolarization of nuclear spin polarized 129 Xe gas by dark rubidium during spin-exchange optical pumping

Antonacci

Burant

Wagner

et al. 2017

Journal of Magnetic Resonance

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Continuous-flow spin-exchange optical pumping (SEOP) continues to serve as the most widespread method of polarizing 129Xe for magnetic resonance experiments. Unfortunately, continuous-flow SEOP still suffers from as-yet unidentified inefficiencies that prevent the production of large volumes of xenon with a nuclear spin polarization close to theoretically calculated values. In this work we use a combination of ultra-low field nuclear magnetic resonance spectroscopy and atomic absorption spectroscopy (AAS) measurements to study the effects of dark Rb vapor on hyperpolarized 129Xe in situ during continuous-flow SEOP. We find that dark Rb vapor in the optical cell outlet has negligible impact on the final 129Xe polarization at typical experimental conditions, but can become significant at higher oven temperatures and lower flow rates. Additionally, in the AAS spectra we also look for a signature of paramagnetic Rb clusters, previously identified as a source of xenon depolarization and a cause for SEOP inefficiency, for which we are able to set an upper limit of 8.3×1015 Rb dimers per cm3.

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Section: Resultssupporting

confidence: 73%

Depolarization of nuclear spin polarized 129 Xe gas by dark rubidium during spin-exchange optical pumping

Antonacci

Burant

Wagner

et al. 2017

Journal of Magnetic Resonance

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“…[An additional contribution may arise from poor energy dissipation caused by reduced thermal conductivity of Xe-rich mixtures-a possibility we are currently studying with in situ Raman spectroscopy (35).] For example, ongoing simulations predict a high Γ SD value of ∼134,300 s −1 for the experimental conditions of the 65°C data in Fig.…”

Section: Discussionmentioning

confidence: 99%

Near-unity nuclear polarization with an open-source ¹²⁹ Xe hyperpolarizer for NMR and MRI

Nikolaou

Coffey

Walkup

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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262

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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) 129Xe 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 D 1 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 (T 1 ∼38 min and ∼5.9 h at ∼1.5 mT and 3 T, respectively)-more than sufficient for a variety of applications.hyperpolarization | laser-polarized xenon | lung imaging | optical pumping O wing to the detection sensitivity provided by their high, nonequilibrium nuclear spin polarization, hyperpolarized (HP) noble gases (e.g., Xe is of particular interest. Moreover, xenon is soluble in blood (6), other tissues (7, 8), and many biologically compatible liquids (9), and its proclivity for interacting with other substances and its wide chemical shift range make HP 129 Xe a sensitive NMR probe of molecular and material surfaces (1,(10)(11)(12) Xe is usually created via spin-exchange optical pumping (SEOP) (23), whereby the unpaired electronic spins of an alkali metal vapor (e.g., Rb) are polarized via optical pumping with circularly polarized light, and the polarization is transferred to noble gas nuclear spins during collisions. It is generally anticipated that high P Xe is achievable only in the low xenon-density regime (18, 24), because (i) higher Xe densities increase the destruction of Rb polarization from nonspin-conserving collisions at a rate that is orders of magnitude worse than those of other gases like N 2 and He (25-27); and (ii) higher total pressures tend to quench the threebody van der Waals contribution to Rb-Xe spin exchange-leaving the less-efficient two-body term (18,23). Most large-scale polarizers, in particular all that are available commercially, operate in this low-Xe density ...

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“…A comparison of Raman spectra acquired using the orthogonal and in-line methods was made under identical conditions at room temperature, with no pump laser illumination and over a 15 s integration time in an optical cell containing 100/1900 Torr Xe/N 2 . The results of this experiment are shown in Figure 7, indicating a~23-fold improvement in SNR [19], facilitating much more accurate determination of temperature. It can be seen from the spectra that additional Raman signals arise from atmospheric N 2 and O 2 along the optical path of the probe laser external to the optical cell.…”

Section: In-line Superheadmentioning

confidence: 90%

“…Rayleigh scattered light was further reduced by an order of magnitude through the inclusion of an ultra-narrow-band beamsplitter filter, which also facilitated the minimization of spontaneous laser diode emissions and fluorescence, thus greatly improving the spectra of the incoming probe photons [19]. Additionally, the entire configuration is mounted on a translational x-axis stage, allowing different positions within the optical cell to be probed independently.…”

Section: In-line Superheadmentioning

confidence: 99%

“…Comparison of typical rotational Raman spectra from N 2 gas at 24°C using the 'orthogonal' detection system (a) or the 'inline' module (b). Spectra were obtained under identical conditions (OP cell containing 100/1900 Torr Xe/N 2 , 15 s acquisition time, no pump laser illumination), and indicate a SNR improvement of~23-fold when using the in-line apparatus [19].…”

Section: In-line Superheadmentioning

confidence: 99%

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Using Raman Spectroscopy to Improve Hyperpolarized Noble Gas Production for Clinical Lung Imaging Techniques

Birchall¹,

Whiting²,

Skinner³

et al. 2017

Raman Spectroscopy and Applications

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Spin-exchange optical pumping (SEOP) can be used to "hyperpolarize" 129Xe for human lung MRI. SEOP involves transfer of angular momentum from light to an alkali metal (Rb) vapor, and then onto 129 Xe nuclear spins during collisions; collisions between excited Rb and N 2 ensure that incident optical energy is nonradiatively converted into heat. However, because variables that govern SEOP are temperature-dependent, the excess heat can complicate efforts to maximize spin polarization-particularly at high laser fluxes and xenon densities. Ultra-low frequency Raman spectroscopy may be used to perform in situ gas temperature measurements to investigate the interplay of energy thermalization and SEOP dynamics. Experimental configurations include an "orthogonal" pump-and-probe design and a newer "inline" design (with source and detector on the same axis) that has provided a >20-fold improvement in SNR. The relationship between 129 Xe polarization and the spatiotemporal distribution of N 2 rotational temperatures has been investigated as a function of incident laser flux, exterior cell temperature, and gas composition. Significantly elevated gas temperatures have been observed -hundreds of degrees hotter than exterior cell surfaces-and variances with position and time can indicate underlying energy transport, convection, and Rb mass-transport processes that, if not controlled, can negatively impact 129 Xe hyperpolarization.

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Comparative study of in situ N2 rotational Raman spectroscopy methods for probing energy thermalisation processes during spin-exchange optical pumping

Cited by 10 publications

References 21 publications

Depolarization of nuclear spin polarized 129 Xe gas by dark rubidium during spin-exchange optical pumping

Depolarization of nuclear spin polarized 129 Xe gas by dark rubidium during spin-exchange optical pumping

Near-unity nuclear polarization with an open-source ¹²⁹ Xe hyperpolarizer for NMR and MRI

Using Raman Spectroscopy to Improve Hyperpolarized Noble Gas Production for Clinical Lung Imaging Techniques

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Comparative study of in situ N2 rotational Raman spectroscopy methods for probing energy thermalisation processes during spin-exchange optical pumping

Cited by 10 publications

References 21 publications

Depolarization of nuclear spin polarized 129 Xe gas by dark rubidium during spin-exchange optical pumping

Depolarization of nuclear spin polarized 129 Xe gas by dark rubidium during spin-exchange optical pumping

Near-unity nuclear polarization with an open-source 129 Xe hyperpolarizer for NMR and MRI

Using Raman Spectroscopy to Improve Hyperpolarized Noble Gas Production for Clinical Lung Imaging Techniques

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Product

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Near-unity nuclear polarization with an open-source ¹²⁹ Xe hyperpolarizer for NMR and MRI