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Purpose: The underlying functional and microstructural lung disease in neonates who are born preterm (bronchopulmonary dysplasia, BPD) remains poorly characterized. Moreover, there is a lack of suitable techniques to reliably assess lung function in this population. Here, we report our preliminary experience with hyperpolarized 129Xe MRI in neonates with BPD. Methods: Neonatal intensive care patients with established BPD were recruited (N = 9) and imaged at a corrected gestational age of median:40.7 (range:37.1, 44.4) wk using a 1.5T neonatal scanner. 2D 129Xe ventilation and diffusion‐weighted images and dissolved phase spectroscopy were acquired, alongside 1H 3D radial UTE. 129Xe images were acquired during a series of short apneic breath‐holds (˜3 s). 1H UTE images were acquired during tidal breathing. Ventilation defects were manually identified and qualitatively compared to lung structures on UTE. ADCs were calculated on a voxel‐wise basis. The signal ratio of the 129Xe red blood cell (RBC) and tissue membrane (M) resonances from spectroscopy was determined. Results: Spiral‐based 129Xe ventilation imaging showed good image quality and sufficient sensitivity to detect mild ventilation abnormalities in patients with BPD. 129Xe ADC values were elevated above that expected given healthy data in older children and adults (median:0.046 [range:0.041, 0.064] cm2s−1); the highest value obtained from an extremely pre‐term patient. 129Xe spectroscopy revealed a low RBC/M ratio (0.14 [0.06, 0.21]). Conclusion: We have demonstrated initial feasibility of 129Xe lung MRI in neonates. With further data, the technique may help guide management of infant lung diseases in the neonatal period and beyond. [ABSTRACT FROM AUTHOR]

Purpose: Imaging of the different resonances of hyperpolarized 129Xe in the brain and lungs was performed using a 3D sampling density‐weighted MRSI technique in healthy volunteers. Methods: Four volunteers underwent dissolved‐phase hyperpolarized 129Xe imaging in the lung with the MRSI technique, which was designed to improve the point‐spread function while preserving SNR (1799 phase‐encoding steps, 14‐s breath hold, 2.1‐cm isotropic resolution). A frequency‐tailored RF excitation pulse was implemented to reliably excite both the 129Xe gas and dissolved phase (tissue/blood signal) with 0.1° and 10° flip angles, respectively. Images of xenon gas in the lung airspaces and xenon dissolved in lung tissue/blood were used to generate quantitative signal ratio maps. The method was also optimized and used for imaging dissolved resonances of 129Xe in the brain in 2 additional volunteers. Results: High‐quality regional spectra of hyperpolarized 129Xe were achieved in both the lung and the brain. Ratio maps of the different xenon resonances were obtained in the lung with sufficient SNR (> 10) at both 1.5 T and 3 T, making a triple Lorentzian fit possible and enabling the measurement of relaxation times and xenon frequency shifts on a voxel‐wise basis. The imaging technique was successfully adapted for brain imaging, resulting in the first demonstration of 3D xenon brain images with a 2‐cm isotropic resolution. Conclusion: Density‐weighted MRSI is an SNR and encoding‐efficient way to image 129Xe resonances in the lung and the brain, providing a valuable tool to quantify regional spectroscopic information. [ABSTRACT FROM AUTHOR]

Hyperpolarized (HP) xenon‐129 (129Xe) brain MRI is a promising imaging modality currently under extensive development. HP 129Xe is nontoxic, capable of dissolving in pulmonary blood, and is extremely sensitive to the local environment. After dissolution in the pulmonary blood, HP 129Xe travels with the blood flow to the brain and can be used for functional imaging such as perfusion imaging, hemodynamic response detection, and blood–brain barrier permeability assessment. HP 129Xe MRI imaging of the brain has been performed in animals, healthy human subjects, and in patients with Alzheimer's disease and stroke. In this review, the overall progress in the field of HP 129Xe brain imaging is discussed, along with various imaging approaches and pulse sequences used to optimize HP 129Xe brain MRI. In addition, current challenges and limitations of HP 129Xe brain imaging are discussed, as well as possible methods for their mitigation. Finally, potential pathways for further development are also discussed. HP 129Xe MRI of the brain has the potential to become a valuable novel perfusion imaging technique and has the potential to be used in the clinical setting in the future. [ABSTRACT FROM AUTHOR]

Purpose: This study describes the development and testing of an asymmetrical xenon‐129 (129Xe) birdcage radiofrequency (RF) coil for 129Xe lung ventilation imaging at 1.5 Tesla, which allows proton (1H) system body coil transmit–receive functionality. Methods: The 129Xe RF coil is a whole‐body asymmetrical elliptical birdcage constructed without an outer RF shield to enable 1H imaging. B1+ field homogeneity and flip angle mapping of the 129Xe birdcage RF coil and 1H system body RF coil with the 129Xe RF coil in situ were evaluated in the MR scanner. The functionality of the 129Xe birdcage RF coil was demonstrated through hyperpolarized 129Xe lung ventilation imaging with the birdcage in both transceiver configuration and transmit‐only configuration when combined with an 8‐channel 129Xe receive‐only RF coil array. The functionality of 1H system body coil with the 129Xe RF coil in situ was demonstrated by acquiring coregistered 1H lung anatomical MR images. Results: The asymmetrical birdcage produced a homogeneous B1+ field (±10%) in agreement with electromagnetic simulations. Simulations indicated an optimal detuning configuration with 4 diodes. The obtained g‐factor of 1.4 for acceleration factor of R = 2 indicates optimal array configuration. Coregistered 1H anatomical images from the system body coil along with 129Xe lung images demonstrated concurrent and compatible arrangement of the RF coils. Conclusion: A large asymmetrical birdcage for homogenous B1+ transmission with high sensitivity reception for 129Xe lung MRI at 1.5 Tesla has been demonstrated. The unshielded asymmetrical birdcage design enables 1H structural lung MR imaging in the same exam. [ABSTRACT FROM AUTHOR]

Purpose: This study develops a tracer kinetic model of xenon uptake in the human brain to determine the transfer rate of inhaled hyperpolarized 129Xe from cerebral blood to gray matter that accounts for the effects of cerebral physiology, perfusion and magnetization dynamics. The 129Xe transfer rate is expressed using a tracer transfer coefficient, which estimates the quantity of hyperpolarized129Xe dissolved in cerebral blood under exchange with depolarized129Xe dissolved in gray matter under equilibrium of concentration. Theory and Methods: Time‐resolved MR spectra of hyperpolarized 129Xe dissolved in the human brain were acquired from three healthy volunteers. Acquired spectra were numerically fitted with five Lorentzian peaks in accordance with known 129Xe brain spectral peaks. The signal dynamics of spectral peaks for gray matter and red blood cells were quantified, and correction for the 129Xe T1 dependence upon blood oxygenation was applied. 129Xe transfer dynamics determined from the ratio of the peaks for gray matter and red blood cells was numerically fitted with the developed tracer kinetic model. Results: For all the acquired NMR spectra, the developed tracer kinetic model fitted the data with tracer transfer coefficients between 0.1 and 0.14. Conclusion: In this study, a tracer kinetic model was developed and validated that estimates the transfer rate of HP 129Xe from cerebral blood to gray matter in the human brain. [ABSTRACT FROM AUTHOR]

Purpose: To measure the transverse relaxation time (T2∗) and apparent diffusion coefficient (ADC) of 19F‐C3F8 gas in vivo in human lungs at 1.5T and 3T, and to determine the representative distribution of values of these parameters in a cohort of healthy volunteers. Methods: Mapping of ADC at lung inflation levels of functional residual capacity (FRC) and total lung capacity (TLC) was performed with inhaled 19F‐C3F8 (eight subjects) and 129Xe (six subjects) at 1.5T. T2∗ mapping with 19F‐C3F8 was performed at 1.5T (at FRC and TLC) for 8 subjects and at 3T (at TLC for seven subjects). Results: At both FRC and TLC, the 19F‐C3F8 ADC was smaller than the free diffusion coefficient demonstrating airway microstructural diffusion restriction. From FRC to TLC, the mean ADC significantly increased from 1.56 mm2/s to 1.83 mm2/s (P =.0017) for 19F‐C3F8, and from 2.49 mm2/s to 3.38 mm2/s (P =.0015) for 129Xe. The posterior‐to‐anterior gradient in ADC for FRC versus TLC in the superior half of the lungs was measured as 0.0308 mm2/s per cm versus 0.0168 mm2/s per cm for 19F‐C3F8 and 0.0871 mm2/s per cm versus 0.0326 mm2/s per cm for 129Xe. A consistent distribution of 19F‐C3F8T2∗ values was observed in the lungs, with low values observed near the diaphragm and large pulmonary vessels. The mean T2∗ across volunteers was 4.48 ms at FRC and 5.33 ms at TLC for 1.5T, and 3.78 ms at TLC for 3T. Conclusion: In this feasibility study, values of physiologically relevant parameters of lung microstructure measurable by MRI (T2∗, and ADC) were established for C3F8 in vivo lung imaging in healthy volunteers. [ABSTRACT FROM AUTHOR]

Purpose: To firstly improve the attainable image SNR of 19F and 1H C3F8 lung imaging at 1.5 tesla using an 8‐element transmit/receive (Tx/Rx) flexible vest array combined with a 6‐element Rx‐only array, and to secondly evaluate microelectromechanical systems for switching the array elements between the 2 resonant frequencies. Methods: The Tx efficiency and homogeneity of the 8‐element array were measured and simulated for 1H imaging in a cylindrical phantom and then evaluated for in vivo 19F/1H imaging. The added improvement provided by the 6‐element Rx‐only array was quantified through simulation and measurement and compared to the ultimate SNR. It was verified through the measurement of isolation that microelectromechanical systems switches provided broadband isolation of Tx/Rx circuitry such that the 19F tuned Tx/Rx array could be effectively used for both 19F and 1H nuclei. Results: For 1H imaging, the measured Tx efficiency/homogeneity (mean ± percent SD; 6.79μT/kW±26%) was comparable to that simulated (7.57μT/kW±20%). The 6 additional Rx‐only loops increased the mean Rx sensitivity when compared to the 8‐element array by a factor of 1.41× and 1.45× in simulation and measurement, respectively. In regions central to the thorax, the simulated SNR of the 14‐element array achieves ≥70% of the ultimate SNR when including noise from the matching circuits and preamplifiers. A measured microelectromechanical systems switching speed of 12 µs and added minimum 22 dB of isolation between Tx and Rx were sufficient for Tx/Rx switching in this application. Conclusion: The described single‐tuned array driven at 19F and 1H, utilizing microelectromechanical systems technology, provides excellent results for 19F and 1H dual‐nuclear lung ventilation imaging. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Purpose: To optimize 19F imaging pulse sequences for perfluoropropane (C3F8) gas human lung ventilation MRI considering intrinsic in vivo relaxation parameters at both 1.5T and 3T. Methods: Optimization of the imaging parameters for both 3D spoiled gradient (SPGR) and steady‐state free precession (SSFP) 19F imaging sequences with inhaled 79% C3F8% and 21% oxygen was performed. Phantom measurements were used to validate simulations of SNR. In vivo parameter mapping and sequence optimization and comparison was performed by imaging the lungs of a healthy adult volunteer. T1 and T2* mapping was performed in vivo to optimize sequence parameters for in vivo lung MRI. The performance of SSFP and SPGR was then evaluated in vivo at 1.5T and 3T. Results: The in vivo T2* of C3F8 was shown to be dependent upon lung inflation level (2.04 ms ± 36% for residual volume and 3.14 ms ± 28% for total lung capacity measured at 3T), with lower T2* observed near the susceptibility interfaces of the diaphragm and around pulmonary blood vessels. Simulation and phantom measurements indicate that a factor of ~2‐3 higher SNR can be achieved with SSFP when compared with optimized SPGR. In vivo lung imaging showed a 1.7 factor of improvement in SNR achieved at 1.5T, while the theoretical improvement at 3T was not attained due to experimental SAR constraints, shorter in vivo T1, and B0 inhomogeneity. Conclusion: SSFP imaging provides increased SNR in lung ventilation imaging of C3F8 demonstrated at 1.5T with optimized SSFP similar to the SNR that can be obtained at 3T with optimized SPGR. [ABSTRACT FROM AUTHOR]

Purpose: To 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. Methods: A 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. Results: The 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. Conclusion: MEMS 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. [ABSTRACT FROM AUTHOR]

Background: To support translational lung MRI research with hyperpolarized 129 Xe gas, comprehensive evaluation of derived quantitative lung function measures against established measures from 3 He MRI is required. Few comparative studies have been performed to date, only at 3T, and multisession repeatability of 129 Xe functional metrics have not been reported.Purpose/hypothesis: To compare hyperpolarized 129 Xe and 3 He MRI-derived quantitative metrics of lung ventilation and microstructure, and their repeatability, at 1.5T.Study Type: Retrospective.Population: Fourteen 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/sequence: 1.5T. NSCLC, COPD patients and selected HN subjects underwent 3D balanced steady-state free-precession lung ventilation MRI using both 3 He and 129 Xe. Selected HN, all ES, and COPD patients underwent 2D multislice spoiled gradient-echo diffusion-weighted lung MRI using both hyperpolarized gas nuclei.Assessment: Ventilated 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 Tests: Intermetric correlations: Spearman's coefficient. Intergroup/internuclei differences: analysis of variance / Wilcoxon's signed rank. Repeatability: coefficient of variation (CV), intraclass correlation (ICC) coefficient.Results: A significant positive correlation between 3 He and 129 Xe VV% was observed (r = 0.860, P < 0.001). VV% was larger for 3 He than 129 Xe (P = 0.001); average bias, 8.79%. A strong correlation between mean 3 He and 129 Xe ADC was obtained (r = 0.922, P < 0.001). MR parameters exhibited good correlations with pulmonary function tests. In COPD patients, mean CV of 3 He and 129 Xe VV% was 4.08% and 13.01%, respectively, with ICC coefficients of 0.541 (P = 0.061) and 0.458 (P = 0.095). Mean 3 He and 129 Xe 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: 129 Xe lung MRI provides near-equivalent information to 3 He for quantitative lung ventilation and microstructural MRI at 1.5T.Level Of Evidence: 3 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2018. [ABSTRACT FROM AUTHOR]

Purpose To compare quantitative fractional ventilation measurements from multiple breath washout imaging (MBW-I) using hyperpolarized 3He with both spoiled gradient echo (SPGR) and balanced steady-state free precession (bSSFP) three-dimensional (3D) pulse sequences and to evaluate the feasibility of MBW-I with hyperpolarized 129Xe. Methods Seven healthy subjects were scanned using 3He MBW-I with 3D SPGR and bSSFP sequences. Five also underwent MBW-I with 129Xe. A dual-tuned coil was used to acquire MBW-I data from both nuclei in the same subject position, enabling direct comparison of regional information. Results High-quality MBW images were obtained with bSSFP sequences using a reduced dose (100 mL) of inhaled hyperpolarized 3He. 3D MBW-I with 129Xe was also successfully demonstrated with a bSSFP sequence. Regional quantitative ventilation measures derived from 3He and 129Xe MBW-I correlated well in all subjects ( P < 0.001) with mean Pearson's correlation coefficients of r = 0.61 and r = 0.52 for 3He SPGR-bSSFP and 129Xe-3He (bSSFP) comparisons. The average intersubject mean difference (and standard deviation) in fractional ventilation in SPGR-bSSFP and 129Xe-3He comparisons was 15% (28%) and 9% (38%), respectively. Conclusions Improved sensitivity in MBW-I can be achieved with polarization-efficient bSSFP sequences. Same scan-session 3D MBW-I with 3He and 129Xe has been demonstrated using a dual-tuned coil. Magn Reson Med 77:2288-2295, 2017. © 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. [ABSTRACT FROM AUTHOR]

Highlights from the article: Assessment of brain perfusion using hyperpolarized 129Xe MRI in a subject with established stroke A map of cerebral blood flow (CBF) was estimated using the recommended parameters.[[5]] Seven contiguous ASL images from the same anatomical location as the SP 129 sp Xe brain image were summed to form an effective slice of thickness of 49 mm, approximately the same as the HP SP 129 sp Xe brain image. In conclusion, we demonstrated the feasibility of performing HP SP 129 sp Xe brain MRI in a clinical subject with an established cerebral pathology, thus introducing a technique that provides a distinct contrast to established imaging methods for regional cerebral tissue perfusion and diffusive gas uptake.

This study presents a novel design of a high impedance surface (HIS) to improve the magnetic field strength of a radio frequency (RF) coil at 63.8 MHz, suitable for 1.5 T magnetic resonance imaging systems. The HIS is miniaturised using distributed interdigital capacitors. A HIS with an electrically small unit cell (l /94) and is positioned between a RF transmit-receive coil and an RF shield. The magnitude of the magnetic field from an RF coil when coupled to a dielectric phantom load (mimicking a biological sample) was estimated using numerical simulation (finite integral methods) and corroborated with measurements. Simulated median improvements in magnetic field inside a dielectric phantom range from approximately 18 to 32% depending on the area of the HIS. [ABSTRACT FROM AUTHOR]

Purpose Upon 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. Methods A 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. Results Spectra 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. Conclusion High 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. [ABSTRACT FROM AUTHOR]

Purpose: The hyperpolarized gases ³He and 129Xe have distinct properties and provide unique and complementary functional information from the lungs. A triple-nuclear, same-breath imaging examination of the lungs with ¹H, ³He, and 129Xe can therefore provide exclusive functional information from the gas images. In addition, the ¹H images provide complementary co-registered structural information in the same physiological time frame. The goal of this study was to design an RF system for triple nuclear lung MRI at 1.5T, consisting of a dual-tuned transceiver coil for ³He and 129Xe, RF switches and a nested ¹H receiver array. Methods: A dual-tuned transmit-receive dual-Helmholtz RF coil for ³He and 129Xe was designed and constructed to work in unison with a nested ¹H receiver array. Results: Triple-nuclear imaging (structural and ventilation) and apparent diffusion coefficient mapping of the human lungs was performed in the same breath-hold using the integrated RF system. B1 maps and volumetric ventilation imaging using a three-dimensional, balanced steady-state free precession pulse sequence performed with both hyperpolarized ³He and 129Xe indicate good stand-alone performance of the coil for the respective nucleus. Conclusion: Triple-nuclear same-breath lung imaging with a dual-tuned coil (³He and 129Xe) and a nested 1H array has been demonstrated with a custom RF system. [ABSTRACT FROM AUTHOR]

Purpose Same-breath acquisition of 1H and hyperpolarized gases (3He and 129Xe) in the lungs provides complementary information on pulmonary structure and function with inherent spatial-temporal registration of the images from the different nuclei. To date 1H images have been acquired using the MR system's body coil, which has low SNR when compared with dedicated receiver-array coils. This study demonstrates the design and application of a dedicated 1H receiver array to improve the 1H lung SNR for use in same-breath acquisition with hyperpolarized gas 3He or 129Xe at 1.5 Tesla. Theory and Methods A four-loop dedicated receiver-array was developed in-house for 1H lung MRI to work in compatibility with existing 3He/129Xe transmit-receive coils. As part of the design process, a new generalized circuit formalism was developed for trap circuits for such a dedicated 1H receiver array at 63.8 MHz with traps for 3He 48.6 MHz and 129Xe 17.7 MHz. Results The 1H lung image SNR from the novel 1H array was twice that observed with the 1H body coil when used in same-breath acquisition with the 3He or 129Xe T-R coil in situ. Conclusion An array coil to improve 1H SNR of the lung in same-breath acquisition with hyperpolarized gases has been demonstrated. Magn Reson Med 74:291-299, 2015. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]