Multiple breath washout of hyperpolarized 129 Xe and 3 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 3 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 129 Xe. METHODS: Seven healthy subjects were scanned using 3 He MBW-I with 3D SPGR and bSSFP sequences. Five also underwent MBW-I with 129 Xe. 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 3 He. 3D MBW-I with 129 Xe was also successfully demonstrated with a bSSFP sequence. Regional quantitative ventilation measures derived from 3 He and 129 Xe 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 3 He SPGR-bSSFP and 129 Xe-3 He (bSSFP) comparisons. The average intersubject mean difference (and standard deviation) in fractional ventilation in SPGR-bSSFP and 129 Xe-3 He 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 3 He and 129 Xe 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.

Multibreath alveolar oxygen tension imaging.

PURPOSE: This study tested the ability of a multibreath hyperpolarized HP (3) He MRI protocol to increase the accuracy of regional alveolar oxygen tension (PA O2 ) measurements by lessening the influence of gas-flow artifacts. Conventional single-breath PA O2 measurement has been susceptible to error induced by intervoxel gas flow, particularly when used to study subjects with moderate-to-severe chronic obstructive pulmonary disease (COPD). METHODS: Both single-breath and multibreath PA O2 imaging schemes were implemented in seven human subjects (one healthy, three asymptomatic smokers, and three COPD). The number and location of voxels with nonphysiologic PA O2 values generated by intervoxel gas flow were compared between the two protocols. RESULTS: The multibreath scheme resulted in a significantly lower total percentage of nonphysiologic PA O2 values (6.0%) than the single-breath scheme (13.7%) (P = 0.006). PA O2 maps showed several patterns of gas-flow artifacts that were present in the single-breath protocol but mitigated by the multibreath approach. Multibreath imaging also allowed for the analysis of slow-filling areas that presented no signal after a single breath. CONCLUSION: A multibreath approach enhances the accuracy and completeness of noninvasive PA O2 measurement by significantly lessening the proportion of nonphysiologic values generated by intervoxel gas flow. Magn Reson Med 76:1092-1101, 2016. © 2015 Wiley Periodicals, Inc.

Fundamentals of aerosol therapy in critical care.

Drug dosing in critically ill patients is challenging due to the altered drug pharmacokinetics-pharmacodynamics associated with systemic therapies. For many drug therapies, there is potential to use the respiratory system as an alternative route for drug delivery. Aerosol drug delivery can provide many advantages over conventional therapy. Given that respiratory diseases are the commonest causes of critical illness, use of aerosol therapy to provide high local drug concentrations with minimal systemic side effects makes this route an attractive option. To date, limited evidence has restricted its wider application. The efficacy of aerosol drug therapy depends on drug-related factors (particle size, molecular weight), device factors, patient-related factors (airway anatomy, inhalation patterns) and mechanical ventilation-related factors (humidification, airway). This review identifies the relevant factors which require attention for optimization of aerosol drug delivery that can achieve better drug concentrations at the target sites and potentially improve clinical outcomes.

Combined measurement of pulmonary inert gas washout and regional ventilation heterogeneity by MR of a single dose of hyperpolarized 3He.

Washout of inert gases is a measure of pulmonary function well-known in lung physiology. This work presents a method combining inert gas washout and spatially resolved imaging using hyperpolarized (3) He, thus providing complementary information on lung function and physiology. The nuclear magnetic resonance signal of intrapulmonary hyperpolarized (3) He is used to track the total amount of gas present within the lungs during multiple-breath washout via tidal breathing. Before the washout phase, 3D ventilation images are acquired using (3) He magnetic resonance imaging from the same dose of inhaled gas. The measured washout signal is corrected for T(1) relaxation and radiofrequency depletion, converting it into a quantity proportional to the apparent amount of gas within the lungs. The use of a pneumotachograph for acquisition of breathing volumes during washout, together with lung volumes derived from the magnetic resonance imaging data, permits assessment of the washout curves against physiological model predictions for healthy lungs. The shape of the resulting washout curves obtained from healthy volunteers matches the predictions, demonstrating the utility of the technique for the quantitative assessment of lung function. The proposed method can be readily integrated with a standard breath-hold (3) He ventilation imaging sequence, thus providing additional information from a single dose of gas.

Cellular effects of helium in different organs.

Experimental research in cardiac and neuronal tissue has shown that besides volatile anesthetics and xenon, the nonanesthetic noble gas helium also reduces ischemia-reperfusion damage. Even though the distinct mechanisms of helium-induced organ protection are not completely unraveled, several signaling pathways have been identified. Beside the protective effects on heart and brain that are mainly obtained by different pre- and postconditioning protocols, helium also exerts effects in the lungs, the immune system, and the blood vessels. Obviously, this noble gas is biochemically not inert and exerts biologic effects, although until today the question remains open on how these changes are mediated. Because of its favorable characteristics and the lack of hemodynamic side effects, helium is suitable for use also in critically ill patients. This review covers the cellular effects of helium, which may lead to new clinical strategies of tissue salvage in ischemia-reperfusion situations, both within and outside the perioperative setting.

Intrapulmonary 3He gas distribution depending on bolus size and temporal bolus placement.

OBJECTIVE: Dynamic ventilation (3)He-MRI is a new method to assess pulmonary gas inflow. As differing airway diameters throughout the ventilatory cycle can influence gas inflow this study intends to investigate the influence of volume and timing of a He gas bolus with respect to the beginning of the tidal volume on inspiratory gas distribution. MATERIALS AND METHODS: An ultrafast 2-dimensional spoiled gradient echo sequence (temporal resolution 100 milliseconds) was used for dynamic ventilation (3)He-MRI of 11 anesthetized and mechanically ventilated pigs. The applied (3)He gas bolus was varied in volume between 100 and 200 mL. A 150-mL bolus was varied in its application time after the beginning of the tidal volume between 0 and 1200 milliseconds. Signal kinetics were evaluated using an in-house developed software after definition of parameters for the quantitative description of (3)He gas inflow. RESULTS: The signal rise time (time interval between signal in the parenchyma reaches 10% and 90% of its maximum) was prolonged with increasing bolus volume. The parameter was shortened with increasing delay of (3)He application after the beginning of the tidal volume. Timing variation as well as volume variation showed no clear interrelation to the signal delay time 10 (time interval between signal in the trachea reaches 50% of its maximum and signal in the parenchyma reaches 10% of its maximum). CONCLUSIONS: Dynamic ventilation (3)He-MRI is able to detect differences in bolus geometry performed by volume variation. Pulmonary gas inflow as investigated by dynamic ventilation (3)He-MRI tends to be accelerated by an increasing application delay of a (3)He gas bolus after the beginning of the tidal volume.

The role of collateral paths in long-range diffusion of 3He in lungs.

RATIONALE AND OBJECTIVES: The hyperpolarized (3)He long-range diffusion coefficient (LRDC) in lungs is sensitive to changes in lung structure due to emphysema, reflecting the increase in collateral paths resulting from tissue destruction. However, no clear understanding of LRDC in healthy lungs has emerged. Here we compare LRDC measured in healthy lungs with computer simulations of diffusion along the airway tree with no collateral connections. MATERIALS AND METHODS: Computer simulations of diffusion of spatially modulated spin magnetization were performed in computer-generated, symmetric-branching models of lungs and compared with existing LRDC measurements in canine and human lungs. RESULTS: The simulations predict LRDC values of order 0.001 cm(2)/sec, approximately 20 times smaller than the measured LRDC. We consider and rule out possible mechanisms for LRDC not included in the simulations: incomplete breath hold, cardiac motion, and passage of dissolved (3)He through airway walls. However, a very low density of small (micron) holes in the airways is shown to account for the observed LRDC. CONCLUSION: It is proposed that LRDC in healthy lungs is determined by small collateral pathways.

The effects of SNR on ADC measurements in diffusion-weighted hyperpolarized He-3 MRI.

The theoretical dependence of the mean and standard deviation of ADC values on signal-to-noise ratio (SNR) was derived and compared to measured values in porous phantoms and the lungs of human subjects using diffusion-weighted hyperpolarized helium-3 MRI. For SNR values below 15, mean ADC values were highly SNR-dependent due to a combination of noise and choice of noise thresholding. Above SNR values of 15 and for mean ADC values within ranges relevant for evaluating lung disease (<0.6 cm2/s), the mean ADC was largely independent of SNR. The standard deviation, by contrast, was highly dependent on SNR over a much larger range, but this dependence was well predicted by theory, suggesting the histogram of ADC values might be corrected for these stochastic processes to more accurately evaluate disease using restricted diffusion measures in the lungs.

The effect of incomplete acetylene washout on cardiac output measurement using open circuit acetylene uptake.

The open circuit acetylene uptake method is a useful non-invasive means of measuring cardiac output. However, because of accumulation of inhaled acetylene in tissues, the cardiac output uptake is underestimated, if residual acetylene is not allowed to wash out completely in between measurements. We determined the effect of applying a correction factor that estimates mixed venous acetylene concentration from endtidal values to the calculation of cardiac output. This accounts for mixed venous acetylene present during measurements made before complete washout. Six healthy subjects performed steady-state exercise at approximately 30% and 60% of V(O2 max). Cardiac output measurements were made at each exercise intensity using the open circuit acetylene uptake method (inspired [acetylene] approximately 1%), with the first and last measurements having no detectible levels of acetylene in expired gas (reference measurement). Data were also obtained with immediate pre-measurement endtidal concentrations ranging from 3% to 15% of the inspired [acetylene], in random order in between. Oxygen consumption, carbon dioxide production and heart rate did not change significantly during testing at each exercise intensity. Reference cardiac output also did not change significantly and averaged 11.1+/-0.8 L/min at 30% of V(O2 max) and 16.5+/-2.0 L/min at 60% of V(O2 max). Uncorrected cardiac output measurements progressively underestimated cardiac output by 15% at the 3% of inspired endtidal [acetylene] and by over 50% at 15% [acetylene] (p<0.0001). However, when corrected for residual endtidal [acetylene], cardiac outputs were not significantly different from the reference measurements. The results of this study suggest that by accounting for residual endtidal acetylene in mixed venous blood, cardiac output can be accurately measured even when washout of acetylene is incomplete, allowing measurements as often as every 10-15 s.

Effect of heliox, oxygen and air breathing on helium bubbles after heliox diving.

In helium saturated rat abdominal adipose tissue, helium bubbles were studied at 101.3 kPa during breathing of either heliox(80:20), 100% oxygen or air after decompression from an exposure to heliox at 405 kPa for one hour. While breathing heliox bubbles initially grew for 15-115 minutes then shrank slowly; three out of 10 bubbles disappeared in the observation period. During oxygen breathing all bubbles initially grew for 10-80 minutes then shrank until they disappeared from view; in the growing phase, oxygen caused faster growth than heliox breathing, but bubbles disappeared sooner with oxygen breathing than with heliox or air breathing. In the shrinking phase, shrinkage is faster with heliox and oxygen breathing than with air breathing. Air breathing caused consistent growth of all bubbles. With heliox and oxygen breathing, most animals survived during the observation period but with air breathing, most animals died of decompression sickness regardless of whether the surrounding atmosphere was helium or air. If recompression beyond the maximum treatment pressure of oxygen is required, these results indicate that a breathing mixture of heliox may be better than air during the treatment of decompression sickness following heliox diving.

Steady-state free precession with hyperpolarized 3He: experiments and theory.

The magnetization response of hyperpolarized 3He gas to a steady-state free precession (SSFP) sequence was simulated using matrix product operators. The simulations included the effects of flip angle (alpha), sequence timings, resonant frequency, gas diffusion coefficient, imaging gradients, T1 and T2. Experiments performed at 1.5 T, on gas phantoms and with healthy human subjects, confirm the predicted theory, and indicate increased SNR with SSFP through use of higher flip angles when compared to optimized spoiled gradient echo (SPGR). Simulations and experiments show some compromise to the SNR and some point spread function broadening at high alpha due to the incomplete refocusing of transverse magnetization, caused by diffusion dephasing from the readout gradient. Mixing of gas polarization levels by diffusion between slices is also identified as a source of signal loss in SSFP at higher alpha through incomplete refocusing. Nevertheless, in the sample experiments, a SSFP sequence with an optimized flip angle of alpha=20 degrees, and 128 sequential phase encoding views, showed a higher SNR when compared to SPGR (alpha=7.2 degrees) with the same bandwidth. Some of the gas sample experiments demonstrated a transient signal response that deviates from theory in the initial phase. This was identified as being caused by radiation damping interactions between the large initial transverse magnetization and the high quality factor (Q=250) birdcage resonator. In 3He NMR experiments, performed without imaging gradients, diffusion dephasing can be mitigated, and the effective T2 is relatively long (1 s). Under these circumstances the SSFP sequence behaves like a CPMG sequence with sinalpha/2 weighting of SNR. Experiments and simulations were also performed to characterize the off-resonance behaviour of the SSFP HP 3He signal. Characteristic banding artifacts due to off-resonance harmonic beating were observed in some of the in vivo SSFP images, for instance in axial slices close to the diaphragm where B0 inhomogeneity is highest. Despite these artifacts, a higher SNR was observed with SSFP in vivo when compared to the SPGR sequence. The trends predicted by theory of increasing SSFP SNR with increasing flip angle were observed in the range alpha=10-20 degrees without compromise to image quality through blurring caused by excessive k-space filtering.

Effect of heliox on albuterol delivery by metered-dose inhaler in pediatric in vitro models of mechanical ventilation.

STUDY OBJECTIVE: To determine the effect of varying concentrations of heliox, a mixture of helium and oxygen, on albuterol delivery administered by metered-dose inhaler (MDI) in pediatric mechanically ventilated models. DESIGN: Prospective in vitro laboratory study. SETTING: University-affiliated research laboratory. MODELS: The lungs of a 10-kg infant and 30-kg child receiving humidified pressure-regulated volume-controlled ventilation were simulated. The infant settings were an endotracheal tube (ETT) of 4.0 mm, tidal volume of 150 ml, positive end-expiratory pressure of 2 cm H(2)O, rate of 20 breaths/minute, inspiratory time of 0.7 second; the child settings were an ETT of 6.0 mm, tidal volume of 450 ml, positive end-expiratory pressure of 2 cm H(2)O, rate of 16 breaths/minute, and inspiratory time of 0.8 second. MEASUREMENTS AND MAIN RESULTS: Ten albuterol MDI canisters with chlorofluorocarbon propellants were each actuated once sequentially (total dose 1000 mug) with a commercially available aerosol holding chamber. Albuterol was collected onto a filter proximal to a lung simulator. The filter was rinsed, and concentrations were determined by high-performance liquid chromatography. In the infant model, heliox mixtures of 70:30, 60:40, and 50:50 were compared with nitrogen:oxygen (N(2):O(2)) mixtures in the same ratios. The effect of the 70:30 mixtures was also explored in a child model. Each gas mixture was tested 5 times. At all three ratios, albuterol delivery to the end of the ETT was improved with heliox compared with N(2):O(2) (approximately 7% vs 3-4%, p<0.0001, one-way analysis of variance [ANOVA] with a Bonferroni correction for multiple comparisons). No significant difference was noted in mean percentage albuterol delivery among the varying ratios of heliox studied. By two-way ANOVA, significantly greater albuterol delivery was noted with 70:30 heliox compared with 70:30 N(2):O(2) (7-8% vs 3%, p<0.0001), with no significant difference between the infant and child model (p=0.21). The gas mixture, model, and interaction of the two explained 88% of the variability in mean percentage albuterol delivery. CONCLUSION: Heliox increased albuterol delivery administered by MDI to the end of the ETT in these in vitro pediatric models of mechanical ventilation. Further studies are needed to determine if the improved albuterol delivery with heliox enhances clinical response in infants and children needing mechanical ventilation.

Measurements and modeling of long range 3He diffusion in the lung using a "slice-washout" method.

In healthy lung tissue, pulsed-gradient-spin-echo (PGSE) methods reveal apparent diffusion coefficients (ADC) of the order 0.20 cm2 s(-1); for diffusion times of approximately 2 ms. For these short diffusion times the ADC is only sensitive to structures approximately (2Dt)1/2 approximately 0.6mm in size. Recent work, using magnetic tagging of the longitudinal magnetization has revealed much smaller ADC values for longer length scales. In this work, the in vivo ADC from within the air-spaces, was measured using a new technique. The signal from a series of images was analyzed from a slice that was repeatedly imaged. Diffusion tends to "top-up" the non-renewable polarization within the slice, which leads to a non-exponential decay in image signal. Image data were compared to 1D finite-difference simulations of diffusion to calculate a long range ADC value. The results yield values of the order 0.034 cm2 s(-1), which are nearly an order of magnitude smaller than those reported by PGSE measurements at shorter diffusion times.

Airway closure in microgravity.

Recent single breath washout (SBW) studies in microgravity and on the ground have suggested an important effect of airway closure on gas mixing in the human lung, reflected particularly in the phase III slope of vital capacity SBW and bolus tests. In order to explore this effect, we designed a SBW in which subjects inspired 2-l from residual volume (RV) starting with a 150 ml bolus of He and SF6. In an attempt to vary the pattern of airways closure configuration before the test, the experiments were conducted in 1G and in microgravity during parabolic flight allowing the pre-test expiration to RV to be either in microgravity or at 1.8 G, with the actual test gas inhalation performed entirely in microgravity. Contrary to our expectations, the measured phase III slope and phase IV height and volume obtained from seven subjects in microgravity were essentially identical irrespective of the gravity level during the pre-test expiration to RV. The results suggest that airway closure configuration at RV before the test inspiration has no apparent impact on phases III and IV generation.

Multiple gas washout during jet ventilation.

Simultaneous washouts of He, N2, and SF6 were monitored during jet ventilation with tidal volumes of 50-200 ml and rates of 1-2 Hz. Gas concentrations were measured from the trachea and from a lower lobe bronchus in six baboons by mass spectrometry. Washouts using large tidal volumes approximated single exponential decays with the relative exponential rates of decay being He fastest, SF4 slowest, and N2 intermediate. Washouts using smaller tidal volumes demonstrated a two-phase exponential decay pattern. During the fast phase, the relative exponential rates of decay were He slowest, SF6 fastest, and N2 intermediate, the reverse order seen during large-volume washouts. During the slow phase, the relative exponential rates of decay were He fastest, SF4 slowest, and N2 intermediate, the same order seen during large-volume washouts. The magnitude of the first phase observed from the lower lobe bronchus was less than that observed from the trachea. These data are consistent with a serial two-compartment transport model incorporating a limitation of molecular diffusion between the peripheral and proximal compartments. The more rapid clearance of less diffusible gases from the central airways during the first phase of washout was due to slower transport from the alveoli to the central airways rather than faster transport from the central airways to the airway opening.

A human acinar structure for simulation of realistic alveolar plateau slopes.

We simulated the intra-acinar contribution to phase III slope (S(acin)) for gases of differing diffusivities (He and SF(6)) by solving equations of diffusive and convective gas transport in multi-branch-point models (MBPM) of the human acinus. We first conducted a sensitivity study of S(acin) to asymmetry and its variability in successive generations. S(acin) increases were greatest when asymmetry and variability of asymmetry were increased at the level of the respiratory bronchioles (generations 17-18) for He and at the level of the alveolar ducts (generations 20-21) for SF(6), corresponding to the location of their respective diffusion fronts. On the basis of this sensitivity study and in keeping with reported acinar morphometry, we built a MBPM that actually reproduced experimental S(acin) values obtained in normal subjects for He, N(2), and SF(6). Ten variants of such a MBPM were constructed to estimate intrinsic S(acin) variability owing to peripheral lung structure. The realistic simulation of S(acin) in the normal lung and the understanding of how asymmetry affects S(acin) for different diffusivity gases make S(acin) a powerful tool to detect structural alterations at different depths in the lung periphery.

Construction and uses of a concentric catheter for gas sampling in lung airways.

A catheter for intra-airway sampling of gas concentrations was constructed from concentric polyethylene tubes. The internal tube (0.58 mm ID, 0.91 mm OD) was connected to a gas analyzer while the external tube (1.20 mm ID, 1.75 mm OD) was constantly flushed by air or a calibration gas, except during sampling. Injection and sampling dead spaces were 0.35 and 0.28 ml, respectively. Delay at 4-ml/min sampling rate was 4.0 +/- 0.2 s. The 0-90% step response to a sudden change in gas composition was 0.24 s when connected to a mass spectrometer. This catheter was used to assess tracer gas dispersion during oscillatory flow (1-20 Hz) in a straight long tube. Local concentrations measured through the catheter, after a small bolus of tracer gas was injected through the external tube, compared favorably with direct measurements through needles inserted via the tube wall and with theoretical predictions. The catheter was also used to measure intra-airway gas concentrations in dog airways during spontaneous breathing, conventional mechanical ventilation, high-frequency ventilation, high-frequency vibration ventilation, and constant-flow ventilation. It ws placed by a fiber-optic bronchoscope and used to measure local quasi-steady concentrations of CO2 and local dispersion with the bolus method. The occurrence of catheter clogging with secretions was substantially reduced with flow through the external tube. Transmitting a calibration gas through the external tube facilitated in situ recalibration of the gas analyzer without removing the catheter. The use of this catheter improved the efficiency and accuracy of measurements of gas concentrations inside lung airways.

Effect of combined recompression and air, oxygen, or heliox breathing on air bubbles in rat tissues.

The fate of bubbles formed in tissues during the ascent from a real or simulated air dive and subjected to therapeutic recompression has only been indirectly inferred from theoretical modeling and clinical observations. We visually followed the resolution of micro air bubbles injected into adipose tissue, spinal white matter, muscle, and tendon of anesthetized rats recompressed to and held at 284 kPa while rats breathed air, oxygen, heliox 80:20, or heliox 50:50. The rats underwent a prolonged hyperbaric air exposure before bubble injection and recompression. In all tissues, bubbles disappeared faster during breathing of oxygen or heliox mixtures than during air breathing. In some of the experiments, oxygen breathing caused a transient growth of the bubbles. In spinal white matter, heliox 50:50 or oxygen breathing resulted in significantly faster bubble resolution than did heliox 80:20 breathing. In conclusion, air bubbles in lipid and aqueous tissues shrink and disappear faster during recompression during breathing of heliox mixtures or oxygen compared with air breathing. The clinical implication of these findings might be that heliox 50:50 is the mixture of choice for the treatment of decompression sickness.

Investigating 3He diffusion NMR in the lungs using finite difference simulations and in vivo PGSE experiments.

Finite difference simulations have been used to model (3)He gas diffusion in simulated lung tissue. The technique has the advantage that a wide range of structural models and diffusion-sensitizing gradient waveforms can be investigated, for which analytical methods would otherwise be virtually impossible. Results from simulations and in vivo pulsed-gradient-spin-echo (PGSE) experiments show that the apparent diffusion coefficient (ADC) is a function of diffusion time and gradient strength, and suggests diffusion is locally anisotropic. The simulations have been compared to recent work on an analytical model that characterizes lung tissue as a series of independent cylinders. The results presented may have clinical implications for (3)He ADC measurements in assessing lung diseases such as chronic-obstructive-pulmonary-disease.

MR imaging of the lungs with hyperpolarized helium-3 gas transported by air.

Hyperpolarized noble gas MRI shows promise in the functional imaging of the pulmonary air spaces. The production of hyperpolarized (HP) gas requires specialized laser optical pumping apparatus, which is not likely to be home built in the majority of clinical MRI radiology centres. There are two routes through which HP gas will be made available to hospitals for clinical use: either the apparatus will be installed locally at a considerable expense to the centre, or a central facility will produce the gas and then deliver it to remote MRI sites as and when required. In this study, the feasibility of transporting large quantities of HP gas for in vivo MR imaging from a remote production facility in Mainz, Germany, by airfreight to Sheffield, UK, was successfully demonstrated.