Purpose To evaluate the feasibility of directly imaging perfusion of human brain tissue by using magnetic resonance (MR) imaging with inhaled hyperpolarized xenon 129 (Xe). Materials and Methods In vivo imaging with Xe was performed in three healthy participants. The combination of a high-yield spin-exchange optical pumpingXe polarizer, custom-built radiofrequency coils, and an optimized gradient-echo MR imaging protocol was used to achieve signal sensitivity sufficient to directly image hyperpolarized Xe dissolved in the human brain. Conventional T1-weighted proton (hydrogen 1 [H]) images and perfusion images by using arterial spin labeling were obtained for comparison. Results Images of Xe uptake were obtained with a signal-to-noise ratio of 31 ± 9 and demonstrated structural similarities to the gray matter distribution on conventional T1-weightedH images and to perfusion images from arterial spin labeling. Conclusion Hyperpolarized Xe MR imaging is an injection-free means of imaging the perfusion of cerebral tissue. The proposed method images the uptake of inhaled xenon gas to the extravascular brain tissue compartment across the intact blood-brain barrier. This level of sensitivity is not readily available with contemporary MR imaging methods.RSNA, 2017.

PurposeUpon inhalation, xenon diffuses into the bloodstream and is transported to the brain, where it dissolves in various compartments of the brain. Although up to five chemically distinct peaks have been previously observed in 129Xe rat head spectra, to date only three peaks have been reported in the human head. This study demonstrates high resolution spectroscopy and chemical shift imaging (CSI) of 129Xe dissolved in the human head at 1.5 Tesla.MethodsA 129Xe radiofrequency coil was built in‐house and 129Xe gas was polarized using spin‐exchange optical pumping. Following the inhalation of 129Xe gas, NMR spectroscopy was performed with spectral resolution of 0.033 ppm. Two‐dimensional CSI in all three anatomical planes was performed with spectral resolution of 2.1 ppm and voxel size 20 mm × 20 mm.ResultsSpectra of hyperpolarized 129Xe dissolved in the human head showed five distinct peaks at 188 ppm, 192 ppm, 196 ppm, 200 ppm, and 217 ppm. Assignment of these peaks was consistent with earlier studies.ConclusionHigh resolution spectroscopy and CSI of hyperpolarized 129Xe dissolved in the human head has been demonstrated. For the first time, five distinct NMR peaks have been observed in 129Xe spectra from the human head in vivo. Magn Reson Med 75:2227–2234, 2016. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

BackgroundTo support translational lung MRI research with hyperpolarized 129Xe gas, comprehensive evaluation of derived quantitative lung function measures against established measures from 3He MRI is required. Few comparative studies have been performed to date, only at 3T, and multisession repeatability of 129Xe functional metrics have not been reported.Purpose/HypothesisTo compare hyperpolarized 129Xe and 3He MRI‐derived quantitative metrics of lung ventilation and microstructure, and their repeatability, at 1.5T.Study TypeRetrospective.PopulationFourteen healthy nonsmokers (HN), five exsmokers (ES), five patients with chronic obstructive pulmonary disease (COPD), and 16 patients with nonsmall‐cell lung cancer (NSCLC).Field Strength/Sequence1.5T. NSCLC, COPD patients and selected HN subjects underwent 3D balanced steady‐state free‐precession lung ventilation MRI using both 3He and 129Xe. Selected HN, all ES, and COPD patients underwent 2D multislice spoiled gradient‐echo diffusion‐weighted lung MRI using both hyperpolarized gas nuclei.AssessmentVentilated volume percentages (VV%) and mean apparent diffusion coefficients (ADC) were derived from imaging. COPD patients performed the whole MR protocol in four separate scan sessions to assess repeatability. Same‐day pulmonary function tests were performed.Statistical TestsIntermetric correlations: Spearman's coefficient. Intergroup/internuclei differences: analysis of variance / Wilcoxon's signed rank. Repeatability: coefficient of variation (CV), intraclass correlation (ICC) coefficient.ResultsA significant positive correlation between 3He and 129Xe VV% was observed (r = 0.860, P < 0.001). VV% was larger for 3He than 129Xe (P = 0.001); average bias, 8.79%. A strong correlation between mean 3He and 129Xe ADC was obtained (r = 0.922, P < 0.001). MR parameters exhibited good correlations with pulmonary function tests. In COPD patients, mean CV of 3He and 129Xe VV% was 4.08% and 13.01%, respectively, with ICC coefficients of 0.541 (P = 0.061) and 0.458 (P = 0.095). Mean 3He and 129Xe ADC values were highly repeatable (mean CV: 2.98%, 2.77%, respectively; ICC: 0.995, P < 0.001; 0.936, P < 0.001).Data Conclusion 129Xe lung MRI provides near‐equivalent information to 3He for quantitative lung ventilation and microstructural MRI at 1.5T. Level of Evidence: 3 Technical Efficacy Stage 2J. Magn. Reson. Imaging 2018;48:632–642.

PurposeTo evaluate the performance of micro‐electromechanical systems (MEMS) switches against PIN diodes for switching a dual‐tuned RF coil between 19F and 1H resonant frequencies for multi‐nuclear lung imaging.MethodsA four‐element fixed‐phase and amplitude transmit–receive RF coil was constructed to provide homogeneous excitation across the lungs, and to serve as a test system for various switching methods. The MR imaging and RF performance of the coil when switched between the 19F and 1H frequencies using MEMS switches, PIN diodes and hardwired configurations were compared.ResultsThe performance of the coil with MEMS or PIN diode switching was comparable in terms of RF measurements, transmit efficiency and image SNR on both 19F and 1H nuclei. When the coil was not switched to the resonance frequency of the respective nucleus being imaged, reductions in the transmit efficiency were observed of 32% at the 19F frequency and 12% at the 1H frequency. The coil provides transmit field homogeneity of ±12.9% at the 1H frequency and ±14.4% at the 19F frequency in phantoms representing the thorax with the air space of the lungs filled with perfluoropropane gas.ConclusionMEMS and PIN diodes were found to provide comparable performance in on‐state configuration, while MEMS were more robust in off‐state high‐powered operation (>1 kW), providing higher isolation and requiring a lower DC switching voltage than is needed for reverse biasing of PIN diodes. In addition, clear benefits of switching between the 19F and 1H resonances were demonstrated, despite the proximity of their Larmor frequencies.

Prognosticating idiopathic pulmonary fibrosis (IPF) is challenging, in part due to a lack of sensitive biomarkers. A recent article in Thorax described how hyperpolarised xenon magnetic resonance spectroscopy may quantify regional gas exchange in IPF lungs. In a population of patients with IPF, we find that the xenon signal from red blood cells diminishes relative to the tissue/plasma signal over a 12-month time period, even when the diffusion factor for carbon monoxide is static over the same time period. We conclude that hyperpolarised 129Xe MR spectroscopy may be sensitive to short-term changes in interstitial gas diffusion in IPF.

This is a repository copy of 129 Xe-Rb spin-exchange optical pumping with high photon efficiency.

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Purpose To assess the feasibility of using dissolved hyperpolarized xenon‐129 (129Xe) MRI to study renal physiology in humans at 3 T. Methods Using a flexible transceiver RF coil, dynamic and spatially resolved 129Xe spectroscopy was performed in the abdomen after inhalation of hyperpolarized 129Xe gas with 3 healthy male volunteers. A transmit‐only receive‐only RF coil array was purpose‐built to focus RF excitation and enhance sensitivity for dynamic imaging of 129Xe uptake in the kidneys using spoiled gradient echo and balanced steady‐state sequences. Results Using spatially resolved spectroscopy, different magnitudes of signal from 129Xe dissolved in red blood cells and tissue/plasma could be identified in the kidneys and the aorta. The spectra from both kidneys showed peaks with similar amplitudes and chemical shift values. Imaging with the purpose‐built coil array was shown to provide more than a 3‐fold higher SNR in the kidneys when compared with surrounding tissues, while further physiological information from the dissolved 129Xe in the lungs and in transit to the kidneys was provided with the transceiver coil. The signal of dissolved hyperpolarized 129Xe could be imaged with both tested sequences for about 40 seconds after inhalation. Conclusion The uptake of 129Xe dissolved in the human kidneys was measured with spectroscopic and imaging experiments, demonstrating the potential of hyperpolarized 129Xe MR as a novel, noninvasive technique to image human kidney tissue perfusion.