Regional Structure-Function in Cystic Fibrosis Lung Disease Using Hyperpolarized 129Xe and Ultrashort Echo Magnetic Resonance Imaging

Cryogenic Media in Biomedical Applications: Current Advances, Challenges, and Future Perspectives

This paper explores the crucial role of cryogenic mediums in driving breakthroughs within the biomedical sector. The objective was to investigate, critically discuss, and present the current knowledge and state-of-the-art practices, along with the challenges and perspectives of the most common applications. Through an extensive literature review, this work aims to supplement existing research, offering a comprehensive and up-to-date understanding of the subject. Biomedical research involving cryogenic mediums is advancing on multiple fronts, including the development of advanced medical technologies, clinical treatments for life-threatening conditions, high-quality biospecimen preservation, and antimicrobial interventions in industrial food processing. These advances open new horizons and present cutting-edge opportunities for research and the medical community. While the current body of evidence showcases the impressive impact of cryogenic mediums, such as nitrogen, helium, argon, and oxygen, on revolutionary developments, reaching definitive conclusions on their efficiency and safety remains challenging due to process complexity and research scarcity with a moderate certainty of evidence. Knowledge gaps further underline the need for additional studies to facilitate cryogenic research in developing innovative technological processes in biomedicine. These advancements have the potential to reshape the modern world and significantly enhance the quality of life for people worldwide.

Initial feasibility and challenges of hyperpolarized 129 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 129 Xe 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 129 Xe ventilation and diffusion-weighted images and dissolved phase spectroscopy were acquired, alongside 1 H 3D radial UTE. 129 Xe images were acquired during a series of short apneic breath-holds (˜3 s). 1 H 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 129 Xe red blood cell (RBC) and tissue membrane (M) resonances from spectroscopy was determined.

RESULTS

Spiral-based 129 Xe ventilation imaging showed good image quality and sufficient sensitivity to detect mild ventilation abnormalities in patients with BPD. 129 Xe ADC values were elevated above that expected given healthy data in older children and adults (median:0.046 [range:0.041, 0.064] cm2 s-1 ); the highest value obtained from an extremely pre-term patient. 129 Xe spectroscopy revealed a low RBC/M ratio (0.14 [0.06, 0.21]).

CONCLUSION

We have demonstrated initial feasibility of 129 Xe lung MRI in neonates. With further data, the technique may help guide management of infant lung diseases in the neonatal period and beyond.

Longitudinal Lung Function Assessment of Patients Hospitalized With COVID-19 Using 1H and 129Xe 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 1H and 129Xe MRI between 6 and 52 weeks following hospitalization?

STUDY DESIGN AND METHODS

Patients who were hospitalized with COVID-19 pneumonia underwent a pulmonary 1H and 129Xe MRI protocol at 6, 12, 25, and 51 weeks following hospital admission in a prospective cohort study between November 2020 and February 2022. The imaging protocol was as follows: 1H ultra-short echo time, contrast-enhanced lung perfusion, 129Xe ventilation, 129Xe diffusion-weighted, and 129Xe spectroscopic imaging of gas exchange.

RESULTS

Nine patients were recruited (age 57 ± 14 [median ± interquartile range] years; six of nine patients were male). Patients underwent MRI at 6 (n = 9), 12 (n = 9), 25 (n = 6), and 51 (n = 8) weeks following hospital admission. Patients with signs of interstitial lung damage were excluded. At 6 weeks, patients exhibited impaired 129Xe gas transfer (RBC to membrane fraction), but lung microstructure was not increased (apparent diffusion coefficient and mean acinar airway dimensions). Minor ventilation abnormalities present in four patients were largely resolved in the 6- to 25-week period. At 12 weeks, all patients with lung perfusion data (n = 6) showed an increase in both pulmonary blood volume and flow compared with 6 weeks, although this was not statistically significant. At 12 weeks, significant improvements in 129Xe gas transfer were observed compared with 6-week examinations; however, 129Xe gas transfer remained abnormally low at weeks 12, 25, and 51.

INTERPRETATION

129Xe gas transfer was impaired up to 1 year following hospitalization in patients who were hospitalized with COVID-19 pneumonia, without evidence of architectural distortion on structural imaging, whereas lung ventilation was normal at 52 weeks.

The argument for utilising magnetic resonance imaging as a tool for monitoring lung structure and function in pediatric patients

INTRODUCTION

Although historically challenging to perform in the lung, technological advancements have made Magnetic Resonance Imaging (MRI) increasingly applicable for pediatric pulmonary imaging. Furthermore, a wide array of functional imaging techniques has become available that may be leveraged alongside structural imaging for increasingly sensitive biomarkers, or as outcome measures in the evaluation of novel therapies.

AREAS COVERED

In this review, recent technical advancements and modern methodologies for structural and functional lung MRI are described. These include ultrashort echo time (UTE) MRI, free-breathing contrast agent-free, functional lung MRI, and hyperpolarized gas MRI, amongst other techniques. Specific examples of the application of these methods in children are provided, principally drawn from recent research in asthma, bronchopulmonary dysplasia, and cystic fibrosis.

EXPERT OPINION

Pediatric lung MRI is rapidly growing, and is well poised for clinical utilization, as well as continued research into early disease detection, disease processes, and novel treatments. Structure/function complementarity makes MRI especially attractive as a tool for increased adoption in the evaluation of pediatric lung disease. Looking toward the future, novel technologies, such as low-field MRI and artificial intelligence, mitigate some of the traditional drawbacks of lung MRI and will aid in improving access to MRI in general, potentially spurring increased adoption and demand for pulmonary MRI in children.

Assessment of pulmonary morphometry using hyperpolarized 129 Xe diffusion-weighted MRI with variable-sampling-ratio compressed sensing patterns

BACKGROUND

Hyperpolarized (HP) ¹²⁹ Xe multiple b-values diffusion-weighted magnetic resonance imaging (DW-MRI) has been widely used for quantifying pulmonary microstructural morphometry. However, the technique requires long acquisition times, making it hard to apply in patients with severe pulmonary diseases, who cannot sustain long breath holds.

PURPOSE

To develop and evaluate the technique of variable-sampling-ratio compressed sensing (VCS) patterns for accelerating HP ¹²⁹ Xe multiple b-values DW-MRI in humans.

METHODS

Optimal variable sampling ratios and corresponding k-space undersampling patterns for each b-value were obtained by retrospective simulations based on the fully sampled (FS) DW-MRI dataset acquired from six young healthy volunteers. Then, the FS datasets were retrospectively undersampled using both VCS patterns and conventional compressed sensing (CS) pattern with a similar average acceleration factor. The quality of reconstructed images with retrospective VCS (rVCS) and CS (rCS) datasets were quantified using mean absolute error (MAE) and structural similarity (SSIM). Pulmonary morphometric parameters were also evaluated between rVCS and FS datasets. In addition, prospective VCS multiple b-values ¹²⁹ Xe DW-MRI datasets were acquired from 14 cigarette smokers and 13 age-matched healthy volunteers. The differences of lung morphological parameters obtained with the proposed method were compared between the groups using independent samples t-test. Pearson correlation coefficient was also utilized for evaluating the correlation of the pulmonary physiological parameters obtained with VCS DW-MRI and pulmonary function tests.

RESULTS

Lower MAE and higher SSIM values were found in the reconstructed images with rVCS measurement when compared to those using conventional rCS measurement. The details and quality of the images obtained with rVCS and FS measurements were found to be comparable. The mean values of the morphological parameters derived from rVCS and FS datasets showed no significant differences (p > 0.05), and the mean differences of measured acinar duct radius, mean linear intercept, surface-to-volume ratio, and apparent diffusion coefficient with cylinder model were -0.87%, -2.42%, 2.04%, and -0.50%, respectively. By using the VCS technique, significant differences were delineated between the pulmonary morphometric parameters of healthy volunteers and cigarette smokers (p < 0.001), while the acquisition time was reduced by four times.

CONCLUSION

A fourfold reduction in acquisition time was achieved using the proposed VCS method while preserving good image quality. Our preliminary results demonstrated that the proposed method can be used for evaluating pulmonary injuries caused by cigarette smoking and may prove to be helpful in diagnosing lung diseases in clinical practice.

Emerging Approaches to Monitor and Modify Care in the Era of Cystic Fibrosis Transmembrane Conductance Regulators

As we characterize the clinical benefits of highly effective modulator therapy (HEMT) in the cystic fibrosis (CF) population, our paradigm for treating and monitoring disease continues to evolve. More sensitive approaches are necessary to detect early disease and clinical progression. This article reviews evolving strategies to assess disease control and progression in the HEMT era. This article also explores developments in pulmonary function monitoring, advanced respiratory imaging, tools for the collection of patient-reported outcomes, and their application to profile individual responses, guide therapeutic decisions, and improve the quality of life of people with CF.

Nichtinvasive funktionelle Lungenbildgebung mit hyperpolarisiertem Xenon

Hintergrund

Die Magnetresonanztomographie (MRT) ist ein nichtinvasives Verfahren mit hervorragendem Weichteilkontrast. Aufgrund der geringen Protonendichte und vielen Luft-Gewebe-Übergängen ist die Anwendung in der Lunge jedoch eingeschränkt, so dass hier häufig röntgenbasierte Methoden eingesetzt werden (mit den bekannten Nachteilen ionisierender Strahlung).

Fragestellung

In dieser Übersichtsarbeit wird die Lungen-MRT mit hyperpolarisiertem Xenon-129 (Xe-MRT) dargestellt. Die Xe-MRT erlaubt einzigartige wertvolle Einblicke in die Mikrostruktur und Funktion der Lunge, einschließlich des Gasaustauschs mit roten Blutkörperchen – Parameter, die mit klinischen Standardmethoden nicht zugänglich sind.

Material und Methoden

Durch die magnetische Markierung, die Hyperpolarisierung, wird das Signal von Xenon-129 um bis zu 100.000-fach verstärkt. Hierbei werden die Elektronen von Rubidium mittels Laserlicht zunächst auf 100 % polarisiert und dann durch Stöße auf Xenon übertragen. Danach wird das hyperpolarisierte Gas in einem Beutel zum Patienten gebracht und eingeatmet, kurz bevor die MRT-Aufnahmen beginnen.

Ergebnisse

Durch spezielle Programmierungen (Sequenzen) in der MRT kann die Ventilation, Mikrostruktur oder der Gasaustausch der Lunge in 3‑D dargestellt werden. Dies ermöglicht z. B. die quantitative Darstellung von Belüftungsdefekten, der Größe der Alveolen, der Gasaufnahme im Gewebe und des Gastransfers ins Blut.

Schlussfolgerung

Die Xe-MRT liefert einzigartige Informationen über den Zustand der Lunge – nichtinvasiv, in vivo und in weniger als einer Minute.

Lung MRI with hyperpolarised gases: current & future clinical perspectives

The use of pulmonary MRI in a clinical setting has historically been limited. Whilst CT remains the gold-standard for structural lung imaging in many clinical indications, technical developments in ultrashort and zero echo time MRI techniques are beginning to help realise non-ionising structural imaging in certain lung disorders. In this invited review, we discuss a complementary technique - hyperpolarised (HP) gas MRI with inhaled ³He and ¹²⁹Xe - a method for functional and microstructural imaging of the lung that has great potential as a clinical tool for early detection and improved understanding of pathophysiology in many lung diseases. HP gas MRI now has the potential to make an impact on clinical management by enabling safe, sensitive monitoring of disease progression and response to therapy. With reference to the significant evidence base gathered over the last two decades, we review HP gas MRI studies in patients with a range of pulmonary disorders, including COPD/emphysema, asthma, cystic fibrosis, and interstitial lung disease. We provide several examples of our experience in Sheffield of using these techniques in a diagnostic clinical setting in challenging adult and paediatric lung diseases.

Bronchopulmonary dysplasia from chest radiographs to magnetic resonance imaging and computed tomography: adding value

Bronchopulmonary dysplasia (BPD) is a common long-term complication of preterm birth. The chest radiograph appearance and survivability have evolved since the first description of BPD in 1967 because of improved ventilation and clinical strategies and the introduction of surfactant in the early 1990s. Contemporary imaging care is evolving with the recognition that comorbidities of tracheobronchomalacia and pulmonary hypertension have a great influence on outcomes and can be noninvasively evaluated with CT and MRI techniques, which provide a detailed evaluation of the lungs, trachea and to a lesser degree the heart. However, echocardiography remains the primary modality to evaluate and screen for pulmonary hypertension. This review is intended to highlight the important findings that chest radiograph, CT and MRI can contribute to precision diagnosis, phenotyping and prognosis resulting in optimal management and therapeutics.

Comparison of Hyperpolarized 3He and 129Xe MR Imaging in Cystic Fibrosis Patients

PURPOSE

In this study, we compared hyperpolarized ³He and ¹²⁹Xe images from patients with cystic fibrosis using two commonly applied magnetic resonance sequences, standard gradient echo (GRE) and balanced steady-state free precession (TrueFISP) to quantify regional similarities and differences in signal distribution and defect analysis.

MATERIALS AND METHODS

Ten patients (7M/3F) with cystic fibrosis underwent hyperpolarized gas MR imaging with both ³He and ¹²⁹Xe. Six had MRI with both GRE, and TrueFISP sequences and four patients had only GRE sequence but not TrueFISP. Ventilation defect percentages (VDPs) were calculated as lung voxels with <60% of the whole-lung hyperpolarized gas signal mean and was measured in all datasets. The voxel signal distributions of both ¹²⁹Xe and ³He gases were visualized and compared using violin plots. VDPs of hyperpolarized 3 He and 129 Xe were compared in Bland-Altman plots; Pearson correlation coefficients were used to evaluate the relationships between inter-gas and inter-scan to assess the reproducibility.

RESULTS

A significant correlation was demonstrated between ¹²⁹Xe VDP and ³He VDP for both GRE and TrueFISP sequences (ρ = 0.78, p<0.0004). The correlation between the GRE and TrueFISP VDP for ³He was ρ = 0.98 and was ρ = 0.91 for ¹²⁹Xe. Overall, ¹²⁹Xe (27.2±9.4) VDP was higher than ³He (24.3±6.9) VDP on average on cystic fibrosis patients.

CONCLUSION

In patients with cystic fibrosis, the selection of hyperpolarized ¹²⁹Xe or ³He gas is most likely inconsequential when it comes to measure the overall lung function by VDP although ¹²⁹Xe may be more sensitive to starker lung defects, particularly when using a TrueFISP sequence.

Cystic fibrosis year in review 2020: Section 2 pulmonary disease, infections, and inflammation

The outlook for those with cystic fibrosis (CF) has never been brighter with ever increasing life expectancy and the approval of the highly effective CFTR modulators, such as elexacaftor/tezacaftor/ivacaftor. With that being said, the progressive pulmonary decline and importance of lung health, infection, and inflammation in CF remains. This review is the second part in a three-part CF Year in Review 2020. Part one focused on the literature related to CFTR modulators while part three will feature the multisystem effects related to CF. This review focuses on articles from Pediatric Pulmonology, including articles from other journals that are of particular interest to clinicians. Herein, we highlight studies published during 2020 related to CF pulmonary disease, infection, treatment, and diagnostics.

Enabling Clinical Technologies for Hyperpolarized 129 Xenon Magnetic Resonance Imaging and Spectroscopy

Hyperpolarization is a technique that can increase nuclear spin polarization with the corresponding gains in nuclear magnetic resonance (NMR) signals by 4-8 orders of magnitude. When this process is applied to biologically relevant samples, the hyperpolarized molecules can be used as exogenous magnetic resonance imaging (MRI) contrast agents. A technique called spin-exchange optical pumping (SEOP) can be applied to hyperpolarize noble gases such as 129 Xe. Techniques based on hyperpolarized 129 Xe are poised to revolutionize clinical lung imaging, offering a non-ionizing, high-contrast alternative to computed tomography (CT) imaging and conventional proton MRI. Moreover, CT and conventional proton MRI report on lung tissue structure but provide little functional information. On the other hand, when a subject breathes hyperpolarized 129 Xe gas, functional lung images reporting on lung ventilation, perfusion and diffusion with 3D readout can be obtained in seconds. In this Review, the physics of SEOP is discussed and the different production modalities are explained in the context of their clinical application. We also briefly compare SEOP to other hyperpolarization methods and conclude this paper with the outlook for biomedical applications of hyperpolarized 129 Xe to lung imaging and beyond.

129Xe MRI as a measure of clinical disease severity for pediatric asthma

BACKGROUND

Measurement of regional lung ventilation with hyperpolarized ¹²⁹Xe magnetic resonance imaging (¹²⁹Xe MRI) in pediatric asthma is poised to advance our understanding of disease mechanisms and pathophysiology in a disorder with diverse clinical phenotypes. ¹²⁹Xe MRI has not been investigated in a pediatric asthma cohort.

OBJECTIVE

We hypothesized that ¹²⁹Xe MRI is feasible and can demonstrate ventilation defects that relate to and predict clinical severity in a pediatric asthma cohort.

METHODS

Thirty-seven children (13 with severe asthma, 8 with mild/moderate asthma, 16 age-matched healthy controls) aged 6 to 17 years old were imaged with ¹²⁹Xe MRI. Ventilation defect percentage (VDP) and image reader score were calculated and compared with clinical measures at baseline and at follow-up.

RESULTS

Children with asthma had higher VDP (P = .002) and number of defects per image slice (defects/slice) (P = .0001) than children without asthma. Children with clinically severe asthma had significantly higher VDP and number of defects/slice than healthy controls. Children with asthma who had a higher number of defects/slice had a higher rate of health care utilization (r = 0.48; P = .03) and oral corticosteroid use (r = 0.43; P = .05) at baseline. Receiver-operating characteristic analysis demonstrated that the VDP and number of defects/slice were predictive of increased health care utilization, asthma, and severe asthma. VDP correlated with FEV₁ (r = -0.35; P = .04) and FEV₁/forced vital capacity ratio (r = -0.41; P = .01).

CONCLUSIONS

¹²⁹Xe MRI correlates with asthma severity, health care utilization, and oral corticosteroid use. Because delineation of clinical severity is often difficult in children, ¹²⁹Xe MRI may be an important biomarker for severity, with potential to identify children at higher risk for exacerbations and improve outcomes.

Quantification of Phenotypic Variability of Lung Disease in Children with Cystic Fibrosis

Cystic fibrosis (CF) lung disease has the greatest impact on the morbidity and mortality of patients suffering from this autosomal-recessive multiorgan disorder. Although CF is a monogenic disorder, considerable phenotypic variability of lung disease is observed in patients with CF, even in those carrying the same mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene or CFTR mutations with comparable functional consequences. In most patients with CF, lung disease progresses from childhood to adulthood, but is already present in infants soon after birth. In addition to the CFTR genotype, the variability of early CF lung disease can be influenced by several factors, including modifier genes, age at diagnosis (following newborn screening vs. clinical symptoms) and environmental factors. The early onset of CF lung disease requires sensitive, noninvasive measures to detect and monitor changes in lung structure and function. In this context, we review recent progress with using multiple-breath washout (MBW) and lung magnetic resonance imaging (MRI) to detect and quantify CF lung disease from infancy to adulthood. Further, we discuss emerging data on the impact of variability of lung disease severity in the first years of life on long-term outcomes and the potential use of this information to improve personalized medicine for patients with CF.

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 129Xe 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. This article reviews the methods and applications of in vivo129Xe MR in humans, with a focus on the physics of polarisation by optical pumping, radiofrequency coil and pulse sequence design, and the in vivo applications of 129Xe MRI and MRS to examine lung ventilation, microstructure and gas exchange, blood oxygenation, and perfusion of the brain and kidneys.

Sensitive structural and functional measurements and 1-year pulmonary outcomes in pediatric cystic fibrosis

BACKGROUND

Two functional measurements (multiple breath washout [MBW] and hyperpolarized ¹²⁹Xe ventilation magnetic resonance imaging [¹²⁹Xe MRI]) have been shown to be more sensitive to cystic fibrosis (CF) lung obstruction than traditional spirometry. However, functional techniques may be sensitive to different underlying structural abnormalities. The purpose of this study was to determine relationships between these functional markers, their pathophysiology, and 1-year clinical outcomes.

METHODS

Spirometry, MBW, ¹²⁹Xe MRI, and ultrashort echo-time (UTE) MRI were obtained in a same-day assessment of 27 pediatric CF patients (ages 11.5±5.0) who had not begun CFTR modulator therapies. UTE MRI was scored for structural abnormalities and functional metrics obtained via spirometry, MBW and ¹²⁹Xe MRI. 1-year outcomes (ΔFEV₁ and pulmonary exacerbations), during which ≈50% initiated modulator therapy, were obtained from the electronic medical record.

RESULTS

MBW, ¹²⁹Xe MRI, and UTE MRI detected clinically significant disease in more subjects (>78%) compared to spirometry (<30%). UTE MRI suggests increased odds of bronchial changes when mucus plugging is present in the same lobe. MBW and ¹²⁹Xe MRI correlated best with mucus plugging, while spirometry correlated best with consolidations. Bronchial abnormalities were associated with future pulmonary exacerbations.

CONCLUSIONS

MBW, ¹²⁹Xe MRI, and UTE MRI are more sensitive for detection of pediatric CF lung disease when compared to spirometry. MBW and ¹²⁹Xe MRI correlated with structural abnormalities which occur in early CF disease, suggesting MBW and ¹²⁹Xe MRI are valuable tools in mild CF lung disease that can guide clinical decision making.