Category Archives: Xe

Mapping the dynamics of methanol and xenon co-adsorption in SWNTs by in-situ continuous-flow hyperpolarized 129Xe NMR

Xu, Shutao, Xin Li, Cheng Sun, Anmin Zheng, Weiping Zhang, Xiuwen Han, Xianchun Liu, and Xinhe Bao. “Mapping the Dynamics of Methanol and Xenon Co-Adsorption in SWNTs by in-Situ Continuous-Flow Hyperpolarized 129Xe NMR.” Physical Chemistry Chemical Physics 21, no. 6 (2019): 3287–93.

https://doi.org/10.1039/C8CP07238H.

A comparative study of the adsorption and desorption processes of methanol in two kinds of nanochannels (i.e. MCM-41 and SWNTs) is performed by in situ continuous-flow laser-hyperpolarized 129Xe NMR. The high sensitivity and short acquisition time of hyperpolarized 129Xe allow for probing the molecular dynamics in a confined geometry under real working conditions. Hyperpolarized 129Xe NMR spectra indicate that the methanol adsorption behavior in nanochannels is determined by the characters of adsorption sites and that the methanol adsorption rate in the nanochannels of SWNTs is faster than in MCM-41. The experimental data shown in this work also indicate that there is a change in gas phase 129Xe NMR signal intensity during the adsorption and desorption of methanol in SWNTs. This may be because there is a strong depolarization of hyperpolarized 129Xe in SWNTs.

A portable ventilator with integrated physiologic monitoring for hyperpolarized 129Xe MRI in rodents

Virgincar, Rohan S., Jerry Dahlke, Scott H. Robertson, Nathann Morand, Yi Qi, Simone Degan, Bastiaan Driehuys, and John C. Nouls. “A Portable Ventilator with Integrated Physiologic Monitoring for Hyperpolarized 129Xe MRI in Rodents.” Journal of Magnetic Resonance 295 (October 2018): 63–71.

https://doi.org/10.1016/j.jmr.2018.07.017

Hyperpolarized (HP) 129Xe MRI is emerging as a powerful, non-invasive method to image lung function and is beginning to find clinical application across a range of conditions. As clinical implementation progresses, it becomes important to translate back to well-defined animal models, where novel disease signatures can be characterized longitudinally and validated against histology. To date, preclinical 129Xe MRI has been limited to only a few sites worldwide with 2D imaging that is not generally sufficient to fully capture the heterogeneity of lung disease. To address these limitations and facilitate broader dissemination, we report on a compact and portable HP gas ventilator that integrates all the gas-delivery and physiologic monitoring capabilities required for high-resolution 3D hyperpolarized 129Xe imaging. This ventilator is MR- and HP-gas compatible, driven by inexpensive microcontrollers and open source code, and allows for precise control of the tidal volume and breathing cycle in perorally intubated mice and rats. We use the system to demonstrate data acquisition over multiple breath-holds, during which lung motion is suspended to enable high-resolution 3D imaging of gas-phase and dissolved-phase 129Xe in the lungs. We demonstrate the portability and versatility of the ventilator by imaging a mouse model of lung cancer longitudinally at 2-Tesla, and a healthy rat at 7 T. We also report the detection of subtle spectroscopic fluctuations in phase with the heart rate, superimposed onto larger variations stemming from the respiratory cycle. This ventilator was developed to facilitate duplication and gain broad adoption to accelerate preclinical 129Xe MRI research.

A portable ventilator with integrated physiologic monitoring for hyperpolarized 129Xe MRI in rodents

Virgincar, Rohan S., Jerry Dahlke, Scott H. Robertson, Nathann Morand, Yi Qi, Simone Degan, Bastiaan Driehuys, and John C. Nouls. “A Portable Ventilator with Integrated Physiologic Monitoring for Hyperpolarized 129Xe MRI in Rodents.” Journal of Magnetic Resonance 295 (October 2018): 63–71.

https://doi.org/10.1016/j.jmr.2018.07.017.

Hyperpolarized (HP) 129Xe MRI is emerging as a powerful, non-invasive method to image lung function and is beginning to find clinical application across a range of conditions. As clinical implementation progresses, it becomes important to translate back to well-defined animal models, where novel disease signatures can be characterized longitudinally and validated against histology. To date, preclinical 129Xe MRI has been limited to only a few sites worldwide with 2D imaging that is not generally sufficient to fully capture the heterogeneity of lung disease. To address these limitations and facilitate broader dissemination, we report on a compact and portable HP gas ventilator that integrates all the gas-delivery and physiologic monitoring capabilities required for high-resolution 3D hyperpolarized 129Xe imaging. This ventilator is MR- and HP-gas compatible, driven by inexpensive microcontrollers and open source code, and allows for precise control of the tidal volume and breathing cycle in perorally intubated mice and rats. We use the system to demonstrate data acquisition over multiple breath-holds, during which lung motion is suspended to enable high-resolution 3D imaging of gas-phase and dissolved-phase 129Xe in the lungs. We demonstrate the portability and versatility of the ventilator by imaging a mouse model of lung cancer longitudinally at 2-Tesla, and a healthy rat at 7 T. We also report the detection of subtle spectroscopic fluctuations in phase with the heart rate, superimposed onto larger variations stemming from the respiratory cycle. This ventilator was developed to facilitate duplication and gain broad adoption to accelerate preclinical 129Xe MRI research.

Considering low-rank, sparse and gas-inflow effects constraints for accelerated pulmonary dynamic hyperpolarized 129Xe MRI

Xiao, Sa, He Deng, Caohui Duan, Junshuai Xie, Huiting Zhang, Xianping Sun, Chaohui Ye, and Xin Zhou. “Considering Low-Rank, Sparse and Gas-Inflow Effects Constraints for Accelerated Pulmonary Dynamic Hyperpolarized 129Xe MRI.” Journal of Magnetic Resonance 290 (May 1, 2018): 29–37.

https://doi.org/10.1016/j.jmr.2018.03.003

Dynamic hyperpolarized (HP) 129Xe MRI is able to visualize the process of lung ventilation, which potentially provides unique information about lung physiology and pathophysiology. However, the longitudinal magnetization of HP 129Xe is nonrenewable, making it difficult to achieve high image quality while maintaining high temporal-spatial resolution in the pulmonary dynamic MRI. In this paper, we propose a new accelerated dynamic HP 129Xe MRI scheme incorporating the low-rank, sparse and gas-inflow effects (L + S + G) constraints. According to the gas-inflow effects of HP gas during the lung inspiratory process, a variable-flip-angle (VFA) strategy is designed to compensate for the rapid attenuation of the magnetization. After undersampling k-space data, an effective reconstruction algorithm considering the low-rank, sparse and gas-inflow effects constraints is developed to reconstruct dynamic MR images. In this way, the temporal and spatial resolution of dynamic MR images is improved and the artifacts are lessened. Simulation and in vivo experiments implemented on the phantom and healthy volunteers demonstrate that the proposed method is not only feasible and effective to compensate for the decay of the magnetization, but also has a significant improvement compared with the conventional reconstruction algorithms (P-values are less than 0.05). This confirms the superior performance of the proposed designs and their ability to maintain high quality and temporal-spatial resolution.

Quantitative biosensor detection by chemically exchanging hyperpolarized 129Xe

Korchak, S., et al., Quantitative biosensor detection by chemically exchanging hyperpolarized 129Xe. PCCP, 2018. 20(3): p. 1800-1808.

http://dx.doi.org/10.1039/C7CP07051A

Chemical sensors informing about their local environment are of widespread use for chemical analysis. A thorough understanding of the sensor signaling is fundamental to data analysis and interpretation, and a requirement for technological applications. Here, sensors explored for the recognition and display of biomolecular and cellular markers by magnetic resonance and composed of host molecules for xenon atoms are considered. These host-guest systems are analytically powerful and also function as contrast agents in imaging applications. Using nuclear spin hyperpolarization of 129Xe and chemical exchange saturation transfer the detection sensitivity is orders of magnitude enhanced in comparison to conventional 1H NMR. The sensor signaling reflects this rather complex genesis, furthering the mere qualitative interpretation of biosensing data; to harvest the potential of the approach, however, a detailed numerical account is desired. To this end, we introduce a comprehensive expression that maps the sensor detection quantitatively by integration of the hyperpolarization generation and relaxation with the host-xenon exchange dynamics. As demonstrated for the host molecule and well-established biosensor cryptophane-A, this model reveals a distinguished maximum in sensor signaling and exerts control over experimentation by dedicated adjustments of both the amount of xenon and the duration of the saturation transfer applied in a measurement, for example to capitalize on investigations at the detection limit. Furthermore, usage of the model for data analysis makes the quantification of the sensor concentration in the nanomolar range possible. The approach is readily applicable in investigations using cryptophane-A and is straightaway adaptable to other sensor designs for extension of the field of xenon based biosensing.

Barskiy, D.A., et al., NMR Hyperpolarization Techniques of Gases. Chemistry, 2017. 23(4): p. 725-751.

https://www.ncbi.nlm.nih.gov/pubmed/27711999

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 often be 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 Minireview covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science.

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

Already a bit older this article, but still a good read.

Nikolaou, P., et al., Near-unity nuclear polarization with an open-source 129Xe hyperpolarizer for NMR and MRI. Proc. Nat. Aca. Sci. USA, 2013. 110(35): p. 14150-14155.

http://www.pnas.org/content/110/35/14150.abstract

The exquisite NMR spectral sensitivity and negligible reactivity of hyperpolarized xenon-129 (HP129Xe) make it attractive for a number of magnetic resonance applications; moreover, HP129Xe embodies an alternative to rare and nonrenewable 3He. However, the ability to reliably and inexpensively produce large quantities of HP129Xe with sufficiently high 129Xe nuclear spin polarization (PXe) 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 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 PXe values of ∼90%, ∼57%, ∼50%, and ∼30% have been measured for Xe loadings of ∼300, ∼500, ∼760, and ∼1,570 torr, respectively. PXe 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” 129Xe 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.

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

Antonacci, M.A., et al., Depolarization of nuclear spin polarized 129Xe gas by dark rubidium during spin-exchange optical pumping. J Magn Reson, 2017. 279: p. 60-67.

https://www.ncbi.nlm.nih.gov/pubmed/28475947

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.

Rotaxane probes for protease detection by 129Xe hyperCEST NMR

Slack, C.C., et al., Rotaxane probes for protease detection by 129Xe hyperCEST NMR. Chem Commun (Camb), 2017. 53(6): p. 1076-1079.

https://www.ncbi.nlm.nih.gov/pubmed/28044166

We report a CB6 rotaxane for the 129Xe hyperCEST NMR detection of matrix metalloprotease 2 (MMP-2) activity. MMP-2 is overexpressed in cancer tissue, and hence is a cancer marker. A peptide containing an MMP-2 recognition sequence was incorporated into the rotaxane, synthesized via CB6-promoted click chemistry. Upon cleavage of the rotaxane by MMP-2, CB6 became accessible for 129Xe@CB6 interactions, leading to protease-responsive hyperCEST activation.

Diffusion-mediated 129Xe gas depolarization in magnetic field gradients during continuous-flow optical pumping

Burant, A. and R.T. Branca, Diffusion-mediated 129Xe gas depolarization in magnetic field gradients during continuous-flow optical pumping. J Magn Reson, 2016. 273: p. 124-129.

https://www.ncbi.nlm.nih.gov/pubmed/27825066

The production of large volumes of highly polarized noble gases like helium and xenon is vital to applications of magnetic resonance imaging and spectroscopy with hyperpolarized (HP) gas in humans. In the past ten years, 129Xe has become the gas of choice due to its lower cost, higher availability, relatively high tissue solubility, and wide range of chemical shift values. Though near unity levels of xenon polarization have been achieved in-cell using stopped-flow Spin Exchange Optical Pumping (SEOP), these levels are currently unmatched by continuous-flow SEOP methods. Among the various mechanisms that cause xenon relaxation, such as persistent and transient xenon dimers, wall collisions, and interactions with oxygen, relaxation due to diffusion in magnetic field gradients, caused by rapidly changing magnetic field strength and direction, is often ignored. However, during continuous-flow SEOP production, magnetic field gradients may not have a negligible contribution, especially considering that this methodology requires the combined use of magnets with very different characteristics (low field for spin exchange optical pumping and high field for the reduction of xenon depolarization in the solid state during the freeze out phase) that, when placed together, inevitably create magnetic field gradients along the gas-flow-path. Here, a combination of finite element analysis and Monte Carlo simulations is used to determine the effect of such magnetic field gradients on xenon gas polarization with applications to a specific, continuous-flow hyperpolarization system.

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