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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]

Rationale: Preterm birth is associated with low lung function in childhood, but little is known about the lung microstructure in childhood. Objectives: We assessed the differential associations between the historical diagnosis of bronchopulmonary dysplasia (BPD) and current lung function phenotypes on lung ventilation and microstructure in preterm-born children using hyperpolarized 129Xe ventilation and diffusion-weighted magnetic resonance imaging (MRI) and multiple-breath washout (MBW). Methods: Data were available from 63 children (aged 9-13 yr), including 44 born preterm (<34 weeks' gestation) and 19 termborn control subjects (>37 weeks' gestation). Preterm-born children were classified, using spirometry, as prematurityassociated obstructive lung disease (POLD; FEV1, lower limit of normal [LLN] and FEV1/FVC,LLN), prematurity-associated preserved ratio of impaired spirometry (FEV1,LLN and FEV1/FVC>LLN), preterm-(FEV1>LLN) and term-born control subjects, and those with and without BPD. Ventilation heterogeneity metrics were derived from 129Xe ventilation MRI and SF6 MBW. Alveolar microstructural dimensions were derived from 129Xe diffusion-weighted MRI. Measurements and Main Results: 129Xe ventilation defect percentage and ventilation heterogeneity index were significantly increased in preterm-born children with POLD. In contrast, mean 129Xe apparent diffusion coefficient, 129Xe apparent diffusion coefficient interquartile range, and 129Xe mean alveolar dimension interquartile range were significantly increased in preterm-born children with BPD, suggesting changes of alveolar dimensions. MBW metrics were all significantly increased in the POLD group compared with preterm- and term-born control subjects. Linear regression confirmed the differential effects of obstructive disease on ventilation defects and BPD on lung microstructure. Conclusion: We show that ventilation abnormalities are associated with POLD, and BPD in infancy is associated with abnormal lung microstructure. [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]

Two magnetic resonance specific ventilation imaging (SVI) techniques, namely, oxygen-enhanced proton (OE-1H) and hyperpolarized 3He (HP-3He), were compared in eight healthy supine subjects [age 32 (6) yr]. An in-house radio frequency coil array for 1H configured with the 3He transmit-receive coil in situ enabled acquisition of SVI data from two nuclei from the same slice without repositioning the subjects. After 3 × 3 voxel downsampling to account for spatial registration errors between the two SV images, the voxel-by-voxel correlation coefficient of two SV maps ranged from 0.11 to 0.63 [0.46 mean (0.17 SD); P < 0.05]. Several indexes were analyzed and compared from the tidal volume-matched SV maps: the mean of SV log-normal distribution (SVmean), the standard deviation of the distribution as a measure of SV heterogeneity (SVwidth), and the gravitational gradient (SVslope). There were no significant differences in SVmean [OE-1H: 0.28 (0.08) and HP-3He: 0.32 (0.14)], SVwidths [OE-1H: 0.28 (0.08) and HP-3He: 0.27 (0.10)], and SVslopes [OE-1H: -0.016 (0.006) cm-1 and HP-3He: -0.013 (0.007) cm-1]. Despite the statistical similarities of the population averages, Bland-Altman analysis demonstrated large individual intertechnique variability. SDs of differences in these indexes were 42% (SVmean), 46% (SVwidths), and 62% (SVslopes) of their corresponding overall mean values. The present study showed that two independent, spatially coregistered, SVI techniques presented a moderate positive voxel-by-voxel correlation. Population averages of SVmean, SVwidth, and SVslope were in close agreement. However, the lack of agreement when the data sets were analyzed individually might indicate some fundamental mechanistic differences between the techniques. NEW & NOTEWORTHY To the best of our knowledge, this is the first cross-comparison of two different specific ventilation (SV) MRI techniques in the human lung (i.e., oxygen-enhanced proton and hyperpolarized 3He). The present study showed that two types of spatially coregistered SV images presented a modest positive correlation. The two techniques also yielded similar population averages of SV indexes such as log-normal mean, SV heterogeneity, and the gravitational slope, albeit with some intersubject variability. [ABSTRACT FROM AUTHOR]