Initial feasibility and challenges of hyperpolarized Xe MRI in neonates with bronchopulmonary dysplasia.

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 Xe MRI in neonates with BPD.

Longitudinal Lung Function Assessment of Patients Hospitalized With COVID-19 Using H and Xe Lung MRI.

Background: Microvascular abnormalities and impaired gas transfer have been observed in patients with COVID-19. The progression of pulmonary changes in these patients remains unclear.

Research Question: Do patients hospitalized with COVID-19 without evidence of architectural distortion on structural imaging exhibit longitudinal improvements in lung function measured by using H and Xe MRI between 6 and 52 weeks following hospitalization?

Study Design And Methods: Patients who were hospitalized with COVID-19 pneumonia underwent a pulmonary H and Xe MRI protocol at 6, 12, 25, and 51 weeks following hospital admission in a prospective cohort study between November 2020 and February 2022.

Imaging gas-exchange lung function and brain tissue uptake of hyperpolarized Xe using sampling density-weighted MRSI.

Purpose: Imaging of the different resonances of hyperpolarized Xe 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 Xe 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).

Image Phenotyping of Preterm-Born Children Using Hyperpolarized Xe Lung Magnetic Resonance Imaging and Multiple-Breath Washout.

Preterm birth is associated with low lung function in childhood, but little is known about the lung microstructure in childhood. 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 Xe ventilation and diffusion-weighted magnetic resonance imaging (MRI) and multiple-breath washout (MBW). Data were available from 63 children (aged 9-13 yr), including 44 born preterm (⩽34 weeks' gestation) and 19 term-born control subjects (⩾37 weeks' gestation).

Hyperpolarized Xe imaging of the brain: Achievements and future challenges.

Hyperpolarized (HP) xenon-129 ( Xe) brain MRI is a promising imaging modality currently under extensive development. HP Xe is nontoxic, capable of dissolving in pulmonary blood, and is extremely sensitive to the local environment. After dissolution in the pulmonary blood, HP Xe 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.

An asymmetrical whole-body birdcage RF coil without RF shield for hyperpolarized Xe lung MR imaging at 1.5 T.

Purpose: This study describes the development and testing of an asymmetrical xenon-129 ( Xe) birdcage radiofrequency (RF) coil for Xe lung ventilation imaging at 1.5 Tesla, which allows proton ( H) system body coil transmit-receive functionality.

Methods: The Xe RF coil is a whole-body asymmetrical elliptical birdcage constructed without an outer RF shield to enable H imaging.

In vivo methods and applications of xenon-129 magnetic resonance.

Hyperpolarised gas lung MRI using xenon-129 can provide detailed 3D images of the ventilated lung airspaces, and can be applied to quantify lung microstructure and detailed aspects of lung function such as gas exchange. It is sensitive to functional and structural changes in early lung disease and can be used in longitudinal studies of disease progression and therapy response. The ability of Xe to dissolve into the blood stream and its chemical shift sensitivity to its local environment allow monitoring of gas exchange in the lungs, perfusion of the brain and kidneys, and blood oxygenation.

Measuring Xe transfer across the blood-brain barrier using MR spectroscopy.

Purpose: This study develops a tracer kinetic model of xenon uptake in the human brain to determine the transfer rate of inhaled hyperpolarized Xe from cerebral blood to gray matter that accounts for the effects of cerebral physiology, perfusion and magnetization dynamics. The Xe transfer rate is expressed using a tracer transfer coefficient, which estimates the quantity of hyperpolarized Xe dissolved in cerebral blood under exchange with depolarized Xe dissolved in gray matter under equilibrium of concentration.

Theory And Methods: Time-resolved MR spectra of hyperpolarized Xe dissolved in the human brain were acquired from three healthy volunteers.

MR properties of F C F gas in the lungs of healthy volunteers: and apparent diffusion coefficient at 1.5T and at 3T.

Purpose: To measure the transverse relaxation time ( ) and apparent diffusion coefficient (ADC) of F-C F 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 F-C F (eight subjects) and Xe (six subjects) at 1.

An 8-element Tx/Rx array utilizing MEMS detuning combined with 6 Rx loops for F and H lung imaging at 1.5T.

Purpose: To firstly improve the attainable image SNR of F and H C F 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 H imaging in a cylindrical phantom and then evaluated for in vivo F/ H imaging.

A Magnetic Resonance Imaging Surface Coil Transceiver Employing a Metasurface for 1.5T Applications.

A capacitive impedance metasurface combined with a transceiver coil to improve the radio frequency magnetic field for 1.5T magnetic resonance imaging applications is presented. The novel transceiver provides localized enhancement in magnetic flux density when compared to a transceiver coil alone by incorporating an electrically small metasurface using an interdigital capacitance approach.

Dissolved hyperpolarized xenon-129 MRI in human kidneys.

Purpose: To assess the feasibility of using dissolved hyperpolarized xenon-129 ( Xe) MRI to study renal physiology in humans at 3 T.

Methods: Using a flexible transceiver RF coil, dynamic and spatially resolved Xe spectroscopy was performed in the abdomen after inhalation of hyperpolarized Xe 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 Xe uptake in the kidneys using spoiled gradient echo and balanced steady-state sequences.

Hyperpolarised xenon magnetic resonance spectroscopy for the longitudinal assessment of changes in gas diffusion in IPF.

Prognosticating idiopathic pulmonary fibrosis (IPF) is challenging, in part due to a lack of sensitive biomarkers. A recent article in 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.

Optimization of steady-state free precession MRI for lung ventilation imaging with F C F at 1.5T and 3T.

Purpose: To optimize F imaging pulse sequences for perfluoropropane (C F ) 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) F imaging sequences with inhaled 79% C F and 21% oxygen was performed.

Comparison of quantitative multiple-breath specific ventilation imaging using colocalized 2D oxygen-enhanced MRI and hyperpolarized He MRI.

Two magnetic resonance specific ventilation imaging (SVI) techniques, namely, oxygen-enhanced proton (OE-H) and hyperpolarized He (HP-He), were compared in eight healthy supine subjects [age 32 (6) yr]. An in-house radio frequency coil array for H configured with the He 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.

Comparison of MEMS switches and PIN diodes for switched dual tuned RF coils.

Purpose: To evaluate the performance of micro-electromechanical systems (MEMS) switches against PIN diodes for switching a dual-tuned RF coil between F and H 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 F and H frequencies using MEMS switches, PIN diodes and hardwired configurations were compared.

Comparison of He and Xe MRI for evaluation of lung microstructure and ventilation at 1.5T.

Background: To support translational lung MRI research with hyperpolarized Xe gas, comprehensive evaluation of derived quantitative lung function measures against established measures from He MRI is required. Few comparative studies have been performed to date, only at 3T, and multisession repeatability of Xe functional metrics have not been reported.

Purpose/hypothesis: To compare hyperpolarized Xe and He MRI-derived quantitative metrics of lung ventilation and microstructure, and their repeatability, at 1.

Imaging Human Brain Perfusion with Inhaled Hyperpolarized Xe MR Imaging.

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 pumping Xe 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.

Multiple breath washout of hyperpolarized Xe and He in human lungs with three-dimensional balanced steady-state free-precession imaging.

Purpose: To compare quantitative fractional ventilation measurements from multiple breath washout imaging (MBW-I) using hyperpolarized He 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 Xe.

Methods: Seven healthy subjects were scanned using He MBW-I with 3D SPGR and bSSFP sequences. Five also underwent MBW-I with Xe.

High resolution spectroscopy and chemical shift imaging of hyperpolarized (129) Xe dissolved in the human brain in vivo at 1.5 tesla.

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 (129) Xe 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 (129) Xe dissolved in the human head at 1.

Observation of cardiogenic flow oscillations in healthy subjects with hyperpolarized 3He MRI.

Recently, dynamic MRI of hyperpolarized (3)He during inhalation revealed an alternation of the image intensity between left and right lungs with a cardiac origin (Sun Y, Butler JP, Ferrigno M, Albert MS, Loring SH. Respir Physiol Neurobiol 185: 468-471, 2013). This effect is investigated further using dynamic and phase-contrast flow MRI with inhaled (3)He during slow inhalations (flow rate ∼100 ml/s) to elucidate airflow dynamics in the main lobes in six healthy subjects.

RF instrumentation for same-breath triple nuclear lung MR imaging of (1)H and hyperpolarized (3)He and (129)Xe at 1.5T.

Purpose: The hyperpolarized gases (3)He and (129)Xe have distinct properties and provide unique and complementary functional information from the lungs. A triple-nuclear, same-breath imaging examination of the lungs with (1)H, (3)He, and (129)Xe can therefore provide exclusive functional information from the gas images. In addition, the (1)H images provide complementary co-registered structural information in the same physiological time frame.

Dedicated receiver array coil for H lung imaging with same-breath acquisition of hyperpolarized He and Xe gas.

Purpose: Same-breath acquisition of H and hyperpolarized gases ( He and Xe) 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 H 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 H receiver array to improve the H lung SNR for use in same-breath acquisition with hyperpolarized gas He or Xe at 1.