Madhwesha Rao

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

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.

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

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.

Comparison of 3He and 129Xe MRI for evaluation of lung microstructure and ventilation at 1.5T: 3He and 129Xe Lung MRI at 1.5T

To 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.

Imaging Human Brain Perfusion with Inhaled Hyperpolarized 129Xe 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 (129Xe). Materials and Methods In vivo imaging with 129Xe was performed in three healthy participants. The combination of a high-yield spin-exchange optical pumping 129Xe polarizer, custom-built radiofrequency coils, and an optimized gradient-echo MR imaging protocol was used to achieve signal sensitivity sufficient to directly image hyperpolarized 129Xe dissolved in the human brain. Conventional T1-weighted proton (hydrogen 1 [1H]) images and perfusion images by using arterial spin labeling were obtained for comparison. Results Images of 129Xe uptake were obtained with a signal-to-noise ratio of 31 ± 9 and demonstrated structural similarities to the gray matter distribution on conventional T1-weighted 1H images and to perfusion images from arterial spin labeling. Conclusion Hyperpolarized 129Xe 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.

Multiple breath washout of hyperpolarized (129) Xe and (3) He in human lungs with three-dimensional balanced steady-state free-precession imaging

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.

A high impedance surface for improving the radio frequency magnetic field for a 1.5 Tesla Magnetic Resonance system

This paper focuses on the application of a High Impedance Surface (HIS) to enhance the RF magnetic field (Hi) for a 1.5 Tesla Magnetic Resonance Imaging (MRI) system. The proposed structure is based on a miniaturized HIS using an interdigital capacitance approach. The surface utilizes a HIS between the Radio Frequency (RF) transmit coil and the MRI scanners RF shield which operates at 63.8MHz. The proposed system shows a higher Hi-field inside a homogeneous phantom as compared to a coil above an RF shield. By using this approach, the magnitude of Hi-field was improved by 40%.

Dedicated receiver array coil for 1H lung imaging with same‐breath acquisition of hyperpolarized 3He and 129Xe gas

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 systems 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.

P283 Hyperpolarised Gas MRI – a pathway to Clinical Diagnostic Imaging

Introduction Despite the excellent functional sensitivity of hyperpolarised gas MRI to early lung disease, clinical uptake of the technique has to date been hindered by patents, regulatory classification, availability of 3He and access to polariser technology. However, many of these constraints have been alleviated in recent years, and 129Xe MRI is now providing high quality lung images at relatively low cost. In January 2015 UK regulatory approval for the manufacture of hyperpolarised gases for routine clinical lung imaging was obtained in Sheffield. Here we present a case series as an overview of the clinical questions that this technology can help resolve in various respiratory indications. Methods More than 20 patients (aged 13 to 74) have been clinically referred to date with HP gas MRI in Sheffield to date from NHS hospitals across the UK. Clinical histories include non-CF bronchiectasis (scanned before and after a 2 week course of IV antibiotics), COPD for consideration for LVRS/EB valves, complex asthma (scanned before and after bronchodilator inhalation), CF, patients with poor gas transfer but well-preserved lung parenchyma on CT, IPF overlapping with emphysema. Results Figure 1 shows example images from a cross-section of patients scanned, details of the individual cases will be expanded upon. No adverse events related to imaging were reported. In terms of imaging workflow, scan time average was between 30 min and 1 h 30 min. Patients have been referred from clinics within a 100 km radius and we are also active in enabling novice sites further afield with the technology.Abstract P283 Figure 1 Example of 3He ventilation images; non-CF bronchiectasis patient (a) before and (b) after IV anti biotics, asthma patient (c) before and (d) after bronchodilator, (e) CF patient, and (f) COPD patient I a 129Xe ventilation image (g) COPD patient 2, and a 1H perfusion image (h) patient with poor gas transfer Conclusion Hyperpolarised gas MR provides sensitive, regional images of lung function which can be used to aid in clinical decision making on an individual patient basis. With improvements in gas polarisation, MR hardware and image acquisition techniques routine clinical lung imaging with the cheaper gas isotope 129Xe is also now possible and large scale clinical evaluation of these methods in patient populations are now underway as part of clinical work up.

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

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.

Comparison of Quantitative Multiple Breath Specific Ventilation Imaging Using Co-localized 2D Oxygen Enhanced MRI and Hyperpolarized 3He MRI.

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.