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Pathway to cryogen free production of hyperpolarized Krypton-83 and Xenon-129.

ABSTRACT: Hyperpolarized (hp) (129)Xe and hp (83)Kr for magnetic resonance imaging (MRI) are typically obtained through spin-exchange optical pumping (SEOP) in gas mixtures with dilute concentrations of the respective noble gas. The usage of dilute noble gases mixtures requires cryogenic gas separation after SEOP, a step that makes clinical and preclinical applications of hp (129)Xe MRI cumbersome. For hp (83)Kr MRI, cryogenic concentration is not practical due to depolarization that is caused by quadrupolar relaxation in the condensed phase. In this work, the concept of stopped flow SEOP with concentrated noble gas mixtures at low pressures was explored using a laser with 23.3 W of output power and 0.25 nm linewidth. For (129)Xe SEOP without cryogenic separation, the highest obtained MR signal intensity from the hp xenon-nitrogen gas mixture was equivalent to that arising from 15.5±1.9% spin polarized (129)Xe in pure xenon gas. The production rate of the hp gas mixture, measured at 298 K, was 1.8 cm(3)/min. For hp (83)Kr, the equivalent of 4.4±0.5% spin polarization in pure krypton at a production rate of 2 cm(3)/min was produced. The general dependency of spin polarization upon gas pressure obtained in stopped flow SEOP is reported for various noble gas concentrations. Aspects of SEOP specific to the two noble gas isotopes are discussed and compared with current theoretical opinions. A non-linear pressure broadening of the Rb D(1) transition was observed and taken into account for the qualitative description of the SEOP process.

SUBMITTER: Six JS

PROVIDER: S-EPMC3507956 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:PURPOSE:To derive lobar ventilation in patients with chronic obstructive pulmonary disease (COPD) using a rapid time-series hyperpolarized xenon-129 (HPX) magnetic resonance imaging (MRI) technique and compare this to ventilation/perfusion single-photon emission computed tomography (V/Q-SPECT), correlating the results with high-resolution computed tomography (CT) and pulmonary function tests (PFTs). MATERIALS AND METHODS:Twelve COPD subjects (GOLD stages I-IV) participated in this study and underwent HPX-MRI, V/Q-SPECT/CT, high-resolution CT, and PFTs. HPX-MRI was performed using a novel time-series spiral k-space sampling approach. Relative percentage ventilations were calculated for individual lobe for comparison to the relative SPECT lobar ventilation and perfusion. The absolute HPX-MRI percentage ventilation in each lobe was compared to the absolute CT percentage emphysema score calculated using a signal threshold method. Pearson's correlation and linear regression tests were performed to compare each imaging modality. RESULTS:Strong correlations were found between the relative lobar percentage ventilation with HPX-MRI and percentage ventilation SPECT (r?=?0.644; p?<?0.001) and percentage perfusion SPECT (r?=?0.767; p?<?0.001). The absolute CT percentage emphysema and HPX percentage ventilation correlation was also statistically significant (r?=?0.695, p?<?0.001). The whole lung HPX percentage ventilation correlated with the PFT measurements (FEV1 with r?=?-?0.886, p?<?0.001*, and FEV1/FVC with r?=?-?0.861, p?<?0.001*) better than the whole lung CT percentage emphysema score (FEV1 with r?=?-?0.635, p?=?0.027; and FEV1/FVC with r?=?-?0.652, p?=?0.021). CONCLUSION:Lobar ventilation with HPX-MRI showed a strong correlation with lobar ventilation and perfusion measurements derived from SPECT/CT, and is better than the emphysema score obtained with high-resolution CT. KEY POINTS:• The ventilation hyperpolarized xenon-129 MRI correlates well with ventilation and perfusion with SPECT/CT with the advantage of higher temporal and spatial resolution. • The hyperpolarized xenon-129 MRI correlates with the PFT measurements better than the high-resolution CT with the advantage of avoiding the use of ionizing radiation.

Project description:OBJECTIVES:To investigate the use of a fast dynamic hyperpolarised 129Xe ventilation magnetic resonance imaging (DXeV-MRI) method for detecting and quantifying delayed ventilation in patients with chronic obstructive pulmonary disease (COPD). METHODS:Three male participants (age range 31-43) with healthy lungs and 15 patients (M/F?=?12:3, age range?=?48-73) with COPD (stages II-IV) underwent spirometry tests, quantitative chest computed tomography (QCT), and DXeV-MRI at 1.5-Tesla. Regional delayed ventilation was captured by measuring the temporal signal change in each lung region of interest (ROI) in comparison to that in the trachea. In addition to its qualitative assessment through visual inspection by a clinical radiologist, delayed ventilation was quantitatively captured by calculating a covariance measurement of the lung ROI and trachea signals, and quantified using both the time delay, and the difference between the integrated areas covered by the signal-time curves of the two signals. RESULTS:Regional temporal ventilation, consistent with the expected physiological changes across a free breathing cycle, was demonstrated with DXeV-MRI in all patients. Delayed ventilation was observed in 13 of the 15 COPD patients and involved variable lung ROIs. This was in contrast to the control group, where no delayed ventilation was demonstrated (p =?0.0173). CONCLUSIONS:DXeV-MRI offers a non-invasive way of detecting and quantifying delayed ventilation in patients with COPD, and provides physiological information on regional pulmonary function during a full breathing cycle. KEY POINTS:• Dynamic xenon MRI allows for the non-invasive detection and measurement of delayed ventilation in COPD patients. • Dynamic xenon MRI during a free breathing cycle can provide unique information about pulmonary physiology and pulmonary disease pathophysiology. • With further validation, dynamic xenon MRI could offer a non-invasive way of measuring collateral ventilation which can then be used to guide lung volume reduction therapy (LVRT) for certain COPD patients.

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Pathway to cryogen free production of hyperpolarized Krypton-83 and Xenon-129.

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