Novel magnetic resonance technique for functional imaging of cystic fibrosis lung disease

Lung structural and functional impairments in young children with cystic fibrosis diagnosed following newborn screening - A nationwide observational study

BACKGROUND

Non-invasive and sensitive clinical endpoints are needed to monitor onset and progression of early lung disease in children with cystic fibrosis (CF). We compared lung clearance index (LCI), FEV1, functional and structural lung magnetic resonance imaging (MRI) outcomes in Swiss children with CF diagnosed following newborn screening.

METHODS

Lung function (LCI, FEV1) and unsedated functional and structural lung MRI was performed in 79 clinically stable children with CF (3 - 8 years) and 75 age-matched healthy controls. Clinical information was collected throughout childhood.

RESULTS

LCI, ventilation and perfusion defects, and structural MRI scores were significantly higher in children with CF compared with controls, but FEV1 was not different between groups. Lung MRI outcomes correlated significantly with LCI (morphology score (r = 0.56, p < 0.001); ventilation defects (r = 0.43, p = 0.001); perfusion defects (r = 0.64, p < 0.001), but not with FEV1. Lung MRI outcomes were more sensitive to detect impairments in children with CF (abnormal ventilation and perfusion outcomes in 47 %, morphology score in 30 %) compared with lung function (abnormal LCI in 21 % and FEV1 in 4.8 %). Pulmonary exacerbations, respiratory hospitalizations, and increase in patient-reported cough was associated with higher LCI and higher structural and functional MRI outcomes.

CONCLUSIONS

The LCI and lung MRI outcomes non-invasively detect even mild early lung disease in young children with CF diagnosed following newborn screening. Pulmonary exacerbations and early respiratory symptoms were risk factors for structural and functional impairment in childhood.

Contrast agent-free functional magnetic resonance imaging with matrix pencil decomposition to quantify abnormalities in lung perfusion and ventilation in patients with cystic fibrosis

Background

Previous studies showed that contrast-enhanced (CE) morpho-functional magnetic resonance imaging (MRI) detects abnormalities in lung morphology and perfusion in patients with cystic fibrosis (CF). Novel matrix pencil decomposition MRI (MP-MRI) enables quantification of lung perfusion and ventilation without intravenous contrast agent administration.

Objectives

To compare MP-MRI with established morpho-functional MRI and spirometry in patients with CF.

Methods

Thirty-nine clinically stable patients with CF (mean age 21.6 ± 10.7 years, range 8-45 years) prospectively underwent morpho-functional MRI including CE perfusion MRI, MP-MRI and spirometry. Two blinded chest radiologists assessed morpho-functional MRI and MP-MRI employing the validated chest MRI score. In addition, MP-MRI data were processed by automated software calculating perfusion defect percentage (QDP) and ventilation defect percentage (VDP).

Results

MP perfusion score and QDP correlated strongly with the CE perfusion score (both r = 0.81; p < 0.01). MP ventilation score and VDP showed strong inverse correlations with percent predicted FEV1 (r = -0.75 and r = -0.83; p < 0.01). The comparison of visual and automated parameters showed that both MP perfusion score and QDP, and MP ventilation score and VDP were strongly correlated (r = 0.74 and r = 0.78; both p < 0.01). Further, the MP perfusion score and MP ventilation score, as well as QDP and VDP were strongly correlated (r = 0.88 and r = 0.86; both p < 0.01).

Conclusion

MP-MRI detects abnormalities in lung perfusion and ventilation in patients with CF without intravenous or inhaled contrast agent application, and correlates strongly with the well-established CE perfusion MRI score and spirometry. Automated analysis of MP-MRI may serve as quantitative noninvasive outcome measure for diagnostic monitoring and clinical trials.

Long-term pulmonary outcome of children with congenital diaphragmatic hernia: functional lung MRI using matrix-pencil decomposition enables side-specific assessment of lung function

OBJECTIVES

In patients with congenital diaphragmatic hernia (CDH) the exact functional outcome of the affected lung side is still unknown, mainly due to the lack of spatially resolved diagnostic tools. Functional matrix-pencil decomposition (MP-) lung MRI fills this gap as it measures side-specific ventilation and perfusion. We aimed to assess the overall and side-specific pulmonary long-term outcomes of patients with CDH using lung function tests and MP-MRI.

METHODS

Thirteen school-aged children with CDH (seven with small and six with large defect-sized CDH, defined as > 50% of the chest wall circumference being devoid of diaphragm tissue) and thirteen healthy matched controls underwent spirometry, multiple-breath washout, and MP-MRI. The main outcomes were forced expiratory volume in 1 second (FEV1), lung clearance index (LCI2.5), ventilation defect percentage (VDP), and perfusion defect percentage (QDP).

RESULTS

Patients with a large CDH showed significantly reduced overall lung function compared to healthy controls (mean difference [95%-CIadjusted]: FEV1 (z-score) -4.26 [-5.61, -2.92], FVC (z-score) -3.97 [-5.68, -2.26], LCI2.5 (TO) 1.12 [0.47, 1.76], VDP (%) 8.59 [3.58, 13.60], QDP (%) 17.22 [13.16, 21.27]) and to patients with a small CDH. Side-specific examination by MP-MRI revealed particularly reduced ipsilateral ventilation and perfusion in patients with a large CDH (mean difference to contralateral side [95%-CIadjusted]: VDP (%) 14.80 [10.50, 19.00], QDP (%) 23.50 [1.75, 45.20]).

CONCLUSIONS

Data indicate impaired overall lung function with particular limitation of the ipsilateral side in patients with a large CDH. MP-MRI is a promising tool to provide valuable side-specific functional information in the follow-up of patients with CDH.

CLINICAL RELEVANCE STATEMENT

In patients with congenital diaphragmatic hernia, easily applicable MP-MRI allows specific examination of the lung side affected by the hernia and provides valuable information on ventilation and perfusion with implications for clinical practice, making it a promising tool for routine follow-up.

KEY POINTS

• Functional matrix pencil decomposition (MP) MRI data from a small sample indicate reduced ipsilateral pulmonary ventilation and perfusion in children with large congenital diaphragmatic hernia (CDH). • Easily applicable pencil decomposition MRI provides valuable side-specific diagnostic information on lung ventilation and perfusion. This is a clear advantage over conventional lung function tests, helping to comprehensively follow up patients with congenital diaphragmatic hernia and monitor therapy effects.

Functional lung imaging of 2-year-old children after congenital diaphragmatic hernia repair using dynamic mode decomposition MRI

OBJECTIVES

To investigate the feasibility of non-contrast-enhanced functional lung imaging in 2-year-old children after congenital diaphragmatic hernia (CDH) repair.

METHODS

Fifteen patients after CDH repair were examined using non-contrast-enhanced dynamic magnetic resonance imaging (MRI). For imaging two protocols were used during free-breathing: Protocol A with high temporal resolution and Protocol B with high spatial resolution. The dynamic images were then analysed through a recently developed post-processing method called dynamic mode decomposition (DMD) to obtain ventilation and perfusion maps. The ventilation ratios (VRatio) and perfusion ratios (QRatio) of ipsilateral to contralateral lung were compared to evaluate functional differences. Lastly, DMD MRI-based perfusion results were compared with perfusion parameters obtained using dynamic contrast-enhanced (DCE) MRI to assess agreement between methods.

RESULTS

Both imaging protocols successfully generated pulmonary ventilation (V) and perfusion (Q) maps in all patients. Overall, the VRatio and QRatio values were 0.84 ± 0.19 and 0.70 ± 0.24 for Protocol A, and 0.88 ± 0.18 and 0.72 ± 0.23 for Protocol B, indicating reduced ventilation ( p < 0.05 ) and perfusion ( p < 0.01 ) on the ipsilateral side. Moreover, there is a very strong positive correlation ( r > 0.89 , p < 0.01 ) and close agreement between DMD MRI-based perfusion values and DCE MRI-based perfusion parameters.

CONCLUSIONS

DMD MRI can obtain pulmonary functional information in 2-year-old CDH patients. The results obtained with DMD MRI correlate with DCE MRI, without the need for ionising radiation or exposure to contrast agents. While further studies with larger cohorts are warranted, DMD MRI is a promising option for functional lung imaging in CDH patients.

CLINICAL RELEVANCE STATEMENT

We demonstrate that pulmonary ventilation and perfusion information can be obtained in 2-year-old patients after CDH repair, without the need for ionising radiation or contrast agents by utilising non-contrast-enhanced MRI acquisitions together with dynamic mode decomposition analysis.

KEY POINTS

• Non-contrast-enhanced functional MR imaging is a promising option for functional lung imaging in 2-year-old children after congenital diaphragmatic hernia. • DMD MRI can generate pulmonary ventilation and perfusion maps from free-breathing dynamic acquisitions without the need for ionising radiation or contrast agents. • Lung perfusion parameters obtained with DMD MRI correlate with perfusion parameters obtained using dynamic contrast-enhanced MRI.

Magnetic Resonance Imaging of Lung Perfusion

"Lung perfusion" in the context of imaging conventionally refers to the delivery of blood to the pulmonary capillary bed through the pulmonary arteries originating from the right ventricle required for oxygenation. The most important physiological mechanism in the context of imaging is the so-called hypoxic pulmonary vasoconstriction (HPV, also known as "Euler-Liljestrand-Reflex"), which couples lung perfusion to lung ventilation. In obstructive airway diseases such as asthma, chronic-obstructive pulmonary disease (COPD), cystic fibrosis (CF), and asthma, HPV downregulates pulmonary perfusion in order to redistribute blood flow to functional lung areas in order to conserve optimal oxygenation. Imaging of lung perfusion can be seen as a reflection of lung ventilation in obstructive airway diseases. Other conditions that primarily affect lung perfusion are pulmonary vascular diseases, pulmonary hypertension, or (chronic) pulmonary embolism, which also lead to inhomogeneity in pulmonary capillary blood distribution. Several magnetic resonance imaging (MRI) techniques either dependent on exogenous contrast materials, exploiting periodical lung signal variations with cardiac action, or relying on intrinsic lung voxel attributes have been demonstrated to visualize lung perfusion. Additional post-processing may add temporal information and provide quantitative information related to blood flow. The most widely used and robust technique, dynamic-contrast enhanced MRI, is available in clinical routine assessment of COPD, CF, and pulmonary vascular disease. Non-contrast techniques are important research tools currently requiring clinical validation and cross-correlation in the absence of a viable standard of reference. First data on many of these techniques in the context of observational studies assessing therapy effects have just become available. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 5.

Non-Contrast-Enhanced Functional Lung MRI to Evaluate Treatment Response of Allergic Bronchopulmonary Aspergillosis in Patients With Cystic Fibrosis: A Pilot Study

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) in cystic fibrosis (CF) patients is associated with severe lung damage and requires specific therapeutic management. Repeated imaging is recommended to both diagnose and follow-up response to treatment of ABPA in CF. However, high risk of cumulative radiation exposure requires evaluation of free-radiation techniques in the follow-up of CF patients with ABPA.

PURPOSE

To evaluate whether Fourier decomposition (FD) functional lung MRI can detect response to treatment of ABPA in CF patients.

STUDY TYPE

Retrospective longitudinal.

POPULATION

Twelve patients (7M, median-age:14 years) with CF and ABPA with pre- and post-treatment MRI.

FIELD STRENGTH/SEQUENCE

2D-balanced-steady-state free-precession (bSSFP) sequence with FD at 1.5T.

ASSESSMENT

Ventilation-weighted (V) and perfusion-weighted (Q) maps were obtained after FD processing of 2D-coronal bSSFP time-resolved images acquired before and 3-9 months after treatment. Defects extent was assessed on the functional maps using a qualitative semi-quantitative score (0 = absence/negligible, 1 = <50%, 2 = >50%). Mean and coefficient of variation (CV) of the ventilation signal-intensity (VSI) and the perfusion signal-intensity (QSI) were calculated. Measurements were performed independently by three readers and averaged. Inter-reader reproducibility of the measurements was assessed. Pulmonary function tests (PFTs) were performed within 1 week of both MRI studies as markers of the airflow-limitation severity.

STATISTICAL TESTS

Comparisons of medians were performed using the paired Wilcoxon-test. Reproducibility was assessed using intraclass correlation coefficient (ICC). Correlations between MRI and PFT parameters were assessed using the Spearman-test (rho correlation-coefficient). A P-value <0.05 was considered as significant.

RESULTS

Defects extent on both V and Q maps showed a significant reduction after ABPA treatment (4.25 vs. 1.92 for V-defect-score and 5 vs. 2.75 for Q-defect-score). VSI_mean was significantly increased after treatment (280 vs. 167). Qualitative analyses reproducibility showed an ICC > 0.90, while the ICCs of the quantitative measurements was almost perfect (>0.99). Changes in VSI_cv and QSI_cv before and after treatment correlated inversely with changes of FEV1%p (rho = -0.68 for both).

DATA CONCLUSION

Non-contrast-enhanced FD lung MRI has potential to reproducibly assess response to treatment of ABPA in CF patients and correlates with PFT obstructive parameters.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 3.

Lung Magnetic Resonance Imaging: Technical Advancements and Clinical Applications

ABSTRACT

Since lung magnetic resonance imaging (MRI) became clinically available, limited clinical utility has been suggested for applying MRI to lung diseases. Moreover, clinical applications of MRI for patients with lung diseases or thoracic oncology may vary from country to country due to clinical indications, type of health insurance, or number of MR units available. Because of this situation, members of the Fleischner Society and of the Japanese Society for Magnetic Resonance in Medicine have published new reports to provide appropriate clinical indications for lung MRI. This review article presents a brief history of lung MRI in terms of its technical aspects and major clinical indications, such as (1) what is currently available, (2) what is promising but requires further validation or evaluation, and (3) which developments warrant research-based evaluations in preclinical or patient studies. We hope this article will provide Investigative Radiology readers with further knowledge of the current status of lung MRI and will assist them with the application of appropriate protocols in routine clinical practice.

Lung functional imaging

Pulmonary functional imaging modalities such as computed tomography, magnetic resonance imaging and nuclear imaging can quantitatively assess regional lung functional parameters and their distributions. These include ventilation, perfusion, gas exchange at the microvascular level and biomechanical properties, among other variables. This review describes the rationale, strengths and limitations of the various imaging modalities employed for lung functional imaging. It also aims to explain some of the most commonly measured parameters of regional lung function. A brief review of evidence on the role and utility of lung functional imaging in early diagnosis, accurate lung functional characterisation, disease phenotyping and advancing the understanding of disease mechanisms in major respiratory disorders is provided.

Primary ciliary dyskinesia

BACKGROUND AND OBJECTIVES

Primary ciliary dyskinesia (PCD, ORPHA:244) is a group of rare genetic disorders characterized by dysfunction of motile cilia. It is phenotypically and genetically heterogeneous, with more than 50 genes involved. Thanks to genetic, clinical, and functional characterization, immense progress has been made in the understanding and diagnosis of PCD. Nevertheless, it is underdiagnosed due to the heterogeneous phenotype and complexity of diagnosis. This review aims to help clinicians navigate this heterogeneous group of diseases. Here, we describe the broad spectrum of phenotypes associated with PCD and address pitfalls and difficult-to-interpret findings to avoid misinterpretation.

METHOD

Review of literature CONCLUSION: PCD diagnosis is complex and requires integration of history, clinical picture, imaging, functional and structural analysis of motile cilia and, if available, genetic analysis to make a definitive diagnosis. It is critical that we continue to expand our knowledge of this group of rare disorders to improve the identification of PCD patients and to develop evidence-based therapeutic approaches.

MRI and Pulmonary Function Tests' Results as Ventilation Inhomogeneity Markers in Children and Adolescents with Cystic Fibrosis

Magnetic resonance imaging (MRI) of the chest is becoming more available in the detection and monitoring of early changes in lung function and structure in patients with cystic fibrosis (CF). The aim of this study was to assess the relationship between pulmonary function tests (PFT) and perfusion deficits in CF children measured by MRI. We performed a retrospective analysis of the perfusion lung MRI scans and the results of spirometry, oscillometry, body plethysmography, single-breath carbon monoxide uptake, and multiple-breath washout technique (MBW). There were statistically significant correlations between the MRI perfusion scores and MBW parameters (2.5% LCI, M1/M0, M2/M0), spirometry parameters (FEV1, FVC, FEF25/75), reactance indices in impulse oscillometry (X5Hz, X10Hz), total lung capacity (TLC) measured in single breath carbon monoxide uptake, markers of air-trapping in body plethysmography (RV, RV/TLC), and the diffusing capacity of the lungs for carbon monoxide. We also observed significant differences in the aforementioned PFT variables between the patient groups divided based on perfusion scores. We noted a correlation between markers of functional lung deficits measured by the MRI and PFTs in CF children. MRI perfusion abnormalities were reflected sooner in the course of the disease than PFT abnormalities.

Effects of elexacaftor/tezacaftor/ivacaftor therapy in children with cystic fibrosis - a comprehensive assessment using lung clearance index, spirometry, and functional and structural lung MRI

BACKGROUND

With improvement in supportive therapies and the introduction of cystic fibrosis transmembrane conductance regulator (CFTR)-modulator treatment in patients with cystic fibrosis (CF), milder disease courses are expected. Therefore, sensitive parameters are needed to monitor disease course and effects of CFTR-modulators. Functional lung MRI using matrix-pencil decomposition (MP-MRI) is a promising tool for assessing ventilation and perfusion quantitatively. This study aimed to assess the treatment effect of elexacaftor/tezacaftor/ivacaftor combination regimen (ELX/TEZ/IVA) on measures of structural and functional lung abnormalities.

METHODS

24 children with CF underwent lung function tests (multiple breath washout, spirometry), functional and structural MRI twice (one year apart) before and once after at least two weeks (mean 4.7 ± 2.6 months) on ELX/TEZ/IVA. Main outcomes were changes (Δ) upon ELX/TEZ/IVA in lung function, defect percentage of ventilation (VDP) and perfusion (QDP), defect distribution index of ventilation and perfusion (DDIV, DDIQ), and Eichinger score. Statistical analyses were performed using paired t-tests and multilevel regression models with bootstrapping.

RESULTS

We observed a significant improvement in lung function, structural and functional MRI parameters upon ELX/TEZ/IVA treatment (mean; 95%-CI): ΔLCI2.5 (TO) -0.84 (-1.62 to -0.06); ΔFEV1 (z-score) 1.05 (0.56 to 1.55); ΔVDP (% of impairment) -6.00 (-8.44 to -3.55); ΔQDP (% of impairment) -3.90 (-5.90 to -1.90); ΔDDIV -1.38 (-2.22 to -0.53); ΔDDIQ -0.31 (-0.73 to 0.12); ΔEichinger score -3.89 (-5.05 to -2.72).

CONCLUSIONS

Besides lung function tests, functional and structural MRI is a suitable tool to monitor treatment response of ELX/TEZ/IVA therapy, and seems promising as outcome marker in the future.

129 Xe and Free-Breathing 1 H Ventilation MRI in Patients With Cystic Fibrosis: A Dual-Center Study

BACKGROUND

Free-breathing 1 H ventilation MRI shows promise but only single-center validation has yet been performed against methods which directly image lung ventilation in patients with cystic fibrosis (CF).

PURPOSE

To investigate the relationship between 129 Xe and 1 H ventilation images using data acquired at two centers.

STUDY TYPE

Sequence comparison.

POPULATION

Center 1; 24 patients with CF (12 female) aged 9-47 years. Center 2; 7 patients with CF (6 female) aged 13-18 years, and 6 healthy controls (6 female) aged 21-31 years. Data were acquired in different patients at each center.

FIELD STRENGTH/SEQUENCE

1.5 T, 3D steady-state free precession and 2D spoiled gradient echo.

ASSESSMENT

Subjects were scanned with 129 Xe ventilation and 1 H free-breathing MRI and performed pulmonary function tests. Ventilation defect percent (VDP) was calculated using linear binning and images were visually assessed by H.M., L.J.S., and G.J.C. (10, 5, and 8 years' experience).

STATISTICAL TESTS

Correlations and linear regression analyses were performed between 129 Xe VDP, 1 H VDP, FEV1 , and LCI. Bland-Altman analysis of 129 Xe VDP and 1 H VDP was carried out. Differences in metrics were assessed using one-way ANOVA or Kruskal-Wallis tests.

RESULTS

129 Xe VDP and 1 H VDP correlated strongly with; each other (r = 0.84), FEV1 z-score (129 Xe VDP r = -0.83, 1 H VDP r = -0.80), and LCI (129 Xe VDP r = 0.91, 1 H VDP r = 0.82). Bland-Altman analysis of 129 Xe VDP and 1 H VDP from both centers had a bias of 0.07% and limits of agreement of -16.1% and 16.2%. Linear regression relationships of VDP with FEV1 were not significantly different between 129 Xe and 1 H VDP (P = 0.08), while 129 Xe VDP had a stronger relationship with LCI than 1 H VDP.

DATA CONCLUSION

1 H ventilation MRI shows large-scale agreement with 129 Xe ventilation MRI in CF patients with established lung disease but may be less sensitive to subtle ventilation changes in patients with early-stage lung disease.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

SIMULTANEOUS MULTIPLE BREATH WASHOUT AND OXYGEN-ENHANCED MAGNETIC RESONANCE IMAGING IN HEALTHY ADULTS

Lung function testing and lung imaging are commonly used techniques to monitor respiratory diseases, such as cystic fibrosis (CF). The nitrogen (N₂) multiple-breath washout technique (MBW) has been shown to detect ventilation inhomogeneity in CF, but the underlying pathophysiological processes that are altered are often unclear. Dynamic oxygen-enhanced magnetic resonance imaging (OE-MRI) could potentially be performed simultaneously with MBW because both techniques require breathing of 100% oxygen (O₂) and may allow for visualisation of alterations underlying impaired MBW outcomes. However, simultaneous MBW and OE-MRI has never been assessed, potentially as it requires a magnetic resonance (MR) compatible MBW equipment. In this pilot study, we assessed whether MBW and OE-MRI can be performed simultaneously using a commercial MBW device that has been modified to be MR-compatible. We performed simultaneous measurements in five healthy volunteers aged 25-35 years. We obtained O₂ and N₂ concentrations from both techniques, and generated O₂ wash-in time constant and N₂ washout maps from OE-MRI data. We obtained good quality simultaneous measurements in two healthy volunteers due to technical challenges related to the MBW equipment and poor tolerance. Oxygen and N₂ concentrations from both techniques, as well as O₂ wash-in time constant maps and N₂ washout maps could be obtained, suggesting that simultaneous measurements may have the potential to allow for comparison and visualization of regional differences in ventilation underlying impaired MBW outcomes. Simultaneous MBW and OE-MRI measurements can be performed with a modified MBW device and may help to understand MBW outcomes, but the measurements are challenging and have poor feasibility.

Variability of clinically measured lung clearance index in children with cystic fibrosis

RATIONALE

The lung clearance index (LCI) is increasingly being used in the clinical surveillance of patients with cystic fibrosis (CF). However, there are limited data on long-term variability and physiologically relevant changes in LCI during routine clinical surveillance.

OBJECTIVES

To evaluate the long-term variability of LCI and propose a threshold for a physiologically relevant change.

METHODS

In children aged 4-18 years with CF, LCI was measured every 3 months as part of routine clinical surveillance during 2011-2020 in two centers. The variability of LCI during periods of clinical stability was assessed using mixed-effects models and was used to identify thresholds for physiologically relevant changes.

RESULTS

Repeated LCI measurements of acceptable quality (N = 858) were available in 100 patients with CF; for 74 patients, 399 visits at clinical stability were available. The variability of repeated LCI measurements over time expressed as the coefficient of variation (CV%) was 7.4%. The upper limit of normal (ULN) for relative changes in LCI between visits was 19%.

CONCLUSION

We report the variability of LCI in children and adolescents with CF during routine clinical surveillance. According to our data, a change in LCI beyond 19% may be considered physiologically relevant. These findings will help guide clinical decisions according to LCI changes.

Low Birth Weight and Impaired Later Lung Function: Results from a Monochorionic Twin Study

Rationale: Fetal growth restriction (FGR) and resulting low birth weight are risk factors for impaired lung development. However, both are often correlated with other factors, especially prematurity. Therefore, the question whether lung function changes in individuals with FGR are driven by gestational age, fetal growth, or both often remains unanswered. Objectives: To examine the association of birth weight with lung function in monochorionic twins with selective FGR in one twin. Methods: We included 20 monochorionic twin pairs with selective FGR and subsequent discordant birth weight with a minimum age of 6 years. In this unique case-control design, the smaller twin represents the case and the cotwin the almost identical counterpart. They performed spirometry and underwent body plethysmography, multiple-breath washout, and magnetic resonance imaging (MRI). We compared lung function and MRI outcomes between the smaller twins and their cotwins by paired t tests, and we used mixed linear models to assess the association between birth weight and outcomes. Results: Mean study age was 18.4 years (range, 7.5-29.4), and mean difference in birth weight within the twin pairs was 575 g (range, 270-1,130). The mean difference of forced expiratory volume in 1 second z-score was -0.64 (95% confidence interval [CI], -0.98 to -0.30), and -0.55 (95% CI, -0.92 to -0.18) of forced vital capacity z-score between the smaller twins and their cotwins. Both were associated with birth weight: per 500 g of birth weight, forced expiratory volume in 1 second z-score increased by 0.50 (95% CI, 0.35-0.65; P < 0.001) and forced vital capacity z-score increased by 0.44 (95% CI, 0.31-0.57; P < 0.001). S_acin from multiple-breath washout, as a marker for ventilation inhomogeneity of acinar airways, was elevated in the smaller twins and was associated with low birth weight. There was no difference for MRI outcomes. The results remained similar after adjustment for study height. Conclusions: Low birth weight was associated with reduced large and small airway function independent of gestational age and body growth. Our findings suggest that intrauterine impairment of lung development induced by FGR has significant consequences on lung function until early adulthood.

Phase-cycled balanced SSFP imaging for non-contrast-enhanced functional lung imaging

PURPOSE

To introduce phase-cycled balanced SSFP (bSSFP) acquisition as an alternative in Fourier decomposition MRI for improved robustness against field inhomogeneities.

METHODS

Series 2D dynamic lung images were acquired in 5 healthy volunteers at 1.5 T and 3 T using bSSFP sequence with multiple RF phase increments and compared with conventional single RF phase increment acquisitions. The approach was evaluated based on functional map homogeneity analysis, while ensuring image and functional map quality by means of SNR and contrast-to-noise ratio analyses.

RESULTS

At both field strengths, functional maps obtained with phase-cycled acquisitions displayed improved robustness against local signal losses compared with single-phase acquisitions. The coefficient of variation (mean ± SD, across volunteers) measured in the ventilation maps resulted in 29.7 ± 2.6 at 1.5 T and 37.5 ± 3.1 at 3 T for phase-cycled acquisitions, compared with 39.9 ± 5.2 at 1.5 T and 49.5 ± 3.7 at 3 T for single-phase acquisitions, indicating a significant improvement ( p < 0.05 $$ p<0.05 $$ ) in ventilation map homogeneity.

CONCLUSIONS

Phase-cycled bSSFP acquisitions improve robustness against field inhomogeneity artifacts and significantly improve ventilation map homogeneity at both field strengths. As such, phase-cycled bSSFP may serve as a robust alternative in lung function assessments.

Effects of Elexacaftor/Tezacaftor/Ivacaftor Therapy on Lung Clearance Index and Magnetic Resonance Imaging in Patients with Cystic Fibrosis and One or Two F508del Alleles

RATIONALE

We recently demonstrated that triple combination CFTR modulator therapy with elexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA) improves CFTR function in airway and intestinal epithelia to 40 to 50% of normal in patients with cystic fibrosis (CF) with one or two F508del alleles. In previous studies, this improvement of CFTR function was shown to improve clinical outcomes, however, effects on the lung clearance index (LCI) determined by multiple breath washout and abnormalities in lung morphology and perfusion detected by magnetic resonance imaging (MRI) have not been studied.

OBJECTIVES

To examine the effect of ELX/TEZ/IVA on LCI and lung MRI scores in patients with CF and one or two F508del alleles aged 12 years and older.

METHODS

This prospective, observational, multicenter, post-approval study assessed LCI and lung MRI scores before and 8-16 weeks after initiation of ELX/TEZ/IVA.

MEASUREMENTS AND MAIN RESULTS

A total of 91 patients with CF including 45 heterozygous for F508del and a minimal function mutation (MF) and 46 homozygous for F508del were enrolled in this study. Treatment with ELX/TEZ/IVA improved LCI in F508del/MF (-2.4;IQR, -3.7 - -1.1;P<0.001) and F508del homozygous (-1.4;IQR, -2.4 - -0.4;P<0.001) patients. Further, ELX/TEZ/IVA improved the MRI global score in F508del/MF (-6.0;IQR, -11.0 - -1.3;P<0.001) and F508del homozygous (-6.5;IQR, -11.0 - -1.3;P<0.001) patients.

CONCLUSIONS

Our data demonstrate that improvement of CFTR function by ELX/TEZ/IVA improves lung ventilation and abnormalities in lung morphology including airway mucus plugging and wall thickening in adolescent and adult patients with CF and one or two F508del alleles in a real-world, post-approval setting.

Do clinimetric properties of LCI change after correction of signal processing?

BACKGROUND

The recently described sensor-crosstalk error in the multiple-breath washout (MBW) device Exhalyzer D (Eco Medics AG) could highly influence clinimetric properties and the current interpretation of MBW results. This study reanalyzes MBW data from clinical routine in the corrected software version Spiroware® 3.3.1 and evaluates the effect on outcomes.

METHODS

We included nitrogen-MBW data from healthy children and children with cystic fibrosis (CF) from previously published trials and ongoing cohort studies. We specifically compared lung clearance index (LCI) analyzed in Spiroware 3.2.1 and 3.3.1 with regard to (i) feasibility, (ii) repeatability, and (iii) validity as outcome parameters in children with CF.

RESULTS

(i) All previously collected measurements could be reanalyzed and resulted in unchanged feasibility in Spiroware 3.3.1. (ii) Short- and midterm repeatability of LCI was similar in both software versions. (iii) Clinical validity of LCI remained similar in Spiroware 3.3.1; however, this resulted in lower values. Discrimination between health and disease was comparable between both software versions. The increase in LCI over time was less pronounced with 0.16 LCI units/year (95% confidence interval [CI] 0.08; 0.24) versus 0.30 LCI units/year (95% CI 0.21; 0.38) in 3.2.1. Response to intervention in children receiving CF transmembrane conductance-modulator therapy resulted in a comparable improvement in LCI, in both Spiroware versions.

CONCLUSION

Our study confirms that clinimetric properties of LCI remain unaffected after correction for the cross-sensitivity error in Spiroware software.

MRI Shows Lung Perfusion Changes after Vaping and Smoking

Background Evidence regarding short-term effects of electronic nicotine delivery systems (ENDS) and tobacco smoke on lung ventilation and perfusion is limited. Purpose To examine the immediate effect of ENDS exposure and tobacco smoke on lung ventilation and perfusion by functional MRI and lung function tests. Materials and Methods This prospective observational pilot study was conducted from November 2019 to September 2021 (substudy of randomized controlled trial NCT03589989). Included were 44 healthy adult participants (10 control participants, nine former tobacco smokers, 13 ENDS users, and 12 active tobacco smokers; mean age, 41 years ± 12 [SD]; 28 men) who underwent noncontrast-enhanced matrix pencil MRI and lung function tests before and immediately after the exposure to ENDS products or tobacco smoke. Baseline measurements were acquired after 2 hours of substance abstinence. Postexposure measurements were performed immediately after the exposure. MRI showed semiquantitative measured impairment of lung perfusion (R_Q) and fractional ventilation (R_FV) impairment as percentages of affected lung volume. Lung clearance index (LCI) was assessed by nitrogen multiple-breath washout to capture ventilation inhomogeneity and spirometry to assess airflow limitation. Absolute differences were calculated with paired Wilcoxon signed-rank test and differences between groups with unpaired Mann-Whitney test. Healthy control participants underwent two consecutive MRI measurements to assess MRI reproducibility. Results MRI was performed and lung function measurement was acquired in tobacco smokers and ENDS users before and after exposure. MRI showed a decrease of perfusion after exposure (R_Q, 8.6% [IQR, 7.2%-10.0%] to 9.1% [IQR, 7.8%-10.7%]; P = .03) and no systematic change in R_FV (P = .31) among tobacco smokers. Perfusion increased in participants who used ENDS after exposure (R_Q, 9.7% [IQR, 7.1%-10.9%] to 9.0% [IQR, 6.9%-10.0%]; P = .01). R_FV did not change (P = .38). Only in tobacco smokers was LCI elevated after smoking (P = .02). Spirometry indexes did not change in any participants. Conclusion MRI showed a decrease of lung perfusion after exposure to tobacco smoke and an increase of lung perfusion after use of electronic nicotine delivery systems. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Kligerman in this issue.

State-of-the-art review of lung imaging in cystic fibrosis with recommendations for pulmonologists and radiologists from the "iMAging managEment of cySTic fibROsis" (MAESTRO) consortium

OBJECTIVE

Imaging represents an important noninvasive means to assess cystic fibrosis (CF) lung disease, which remains the main cause of morbidity and mortality in CF patients. While the development of new imaging techniques has revolutionised clinical practice, advances have posed diagnostic and monitoring challenges. The authors aim to summarise these challenges and make evidence-based recommendations regarding imaging assessment for both clinicians and radiologists.

STUDY DESIGN

A committee of 21 experts in CF from the 10 largest specialist centres in Italy was convened, including a radiologist and a pulmonologist from each centre, with the overall aim of developing clear and actionable recommendations for lung imaging in CF. An a priori threshold of at least 80% of the votes was required for acceptance of each statement of recommendation.

RESULTS

After a systematic review of the relevant literature, the committee convened to evaluate 167 articles. Following five RAND conferences, consensus statements were developed by an executive subcommittee. The entire consensus committee voted and approved 28 main statements.

CONCLUSIONS

There is a need for international guidelines regarding the appropriate timing and selection of imaging modality for patients with CF lung disease; timing and selection depends upon the clinical scenario, the patient's age, lung function and type of treatment. Despite its ubiquity, the use of the chest radiograph remains controversial. Both computed tomography and magnetic resonance imaging should be routinely used to monitor CF lung disease. Future studies should focus on imaging protocol harmonisation both for computed tomography and for magnetic resonance imaging. The introduction of artificial intelligence imaging analysis may further revolutionise clinical practice by providing fast and reliable quantitative outcomes to assess disease status. To date, there is no evidence supporting the use of lung ultrasound to monitor CF lung disease.

MRI lung lobe segmentation in pediatric cystic fibrosis patients using a recurrent neural network trained with publicly accessible CT datasets

Purpose

To introduce a widely applicable workflow for pulmonary lobe segmentation of MR images using a recurrent neural network (RNN) trained with chest CT datasets. The feasibility is demonstrated for 2D coronal ultrafast balanced SSFP (ufSSFP) MRI.

Methods

Lung lobes of 250 publicly accessible CT datasets of adults were segmented with an open‐source CT‐specific algorithm. To match 2D ufSSFP MRI data of pediatric patients, both CT data and segmentations were translated into pseudo‐MR images that were masked to suppress anatomy outside the lung. Network‐1 was trained with pseudo‐MR images and lobe segmentations and then applied to 1000 masked ufSSFP images to predict lobe segmentations. These outputs were directly used as targets to train Network‐2 and Network‐3 with non‐masked ufSSFP data as inputs, as well as an additional whole‐lung mask as input for Network‐2. Network predictions were compared to reference manual lobe segmentations of ufSSFP data in 20 pediatric cystic fibrosis patients. Manual lobe segmentations were performed by splitting available whole‐lung segmentations into lobes.

Results

Network‐1 was able to segment the lobes of ufSSFP images, and Network‐2 and Network‐3 further increased segmentation accuracy and robustness. The average all‐lobe Dice similarity coefficients were 95.0 ± 2.8 (mean ± pooled SD [%]) and 96.4 ± 2.5, 93.0 ± 2.0; and the average median Hausdorff distances were 6.1 ± 0.9 (mean ± SD [mm]), 5.3 ± 1.1, 7.1 ± 1.3 for Network‐1, Network‐2, and Network‐3, respectively.

Conclusion

Recurrent neural network lung lobe segmentation of 2D ufSSFP imaging is feasible, in good agreement with manual segmentations. The proposed workflow might provide access to automated lobe segmentations for various lung MRI examinations and quantitative analyses.

Assessment of Lung Structure and Regional Function Using 0.55 T MRI in Patients With Lymphangioleiomyomatosis

OBJECTIVES

Contemporary lower-field magnetic resonance imaging (MRI) may offer advantages for lung imaging by virtue of the improved field homogeneity. The aim of this study was to evaluate the utility of lower-field MRI for combined morphologic imaging and regional lung function assessment. We evaluate low-field MRI in patients with lymphangioleiomyomatosis (LAM), a rare lung disease associated with parenchymal cysts and respiratory failure.

MATERIALS AND METHODS

We performed lung imaging on a prototype low-field (0.55 T) MRI system in 65 patients with LAM. T2-weighted imaging was used for assessment of lung morphology and to derive cyst scores, the percent of lung parenchyma occupied by cysts. Regional lung function was assessed using oxygen-enhanced MRI with breath-held ultrashort echo time imaging and inhaled 100% oxygen as a T1-shortening MR contrast agent. Measurements of percent signal enhancement from oxygen inhalation and percentage of lung with low oxygen enhancement, indicating functional deficits, were correlated with global pulmonary function test measurements taken within 2 days.

RESULTS

We were able to image cystic abnormalities using T2-weighted MRI in this patient population and calculate cyst score with strong correlation to computed tomography measurements (R = 0.86, P < 0.0001). Oxygen-enhancement maps demonstrated regional deficits in lung function of patients with LAM. Heterogeneity of oxygen enhancement between cysts was observed within individual patients. The percent low-enhancement regions showed modest, but significant, correlation with FEV1 (R = -0.37, P = 0.007), FEV1/FVC (R = -0.33, P = 0.02), and cyst score (R = 0.40, P = 0.02). The measured arterial blood ΔT1 between normoxia and hyperoxia, used as a surrogate for dissolved oxygen in blood, correlated with DLCO (R = -0.28, P = 0.03).

CONCLUSIONS

Using high-performance 0.55 T MRI, we were able to perform simultaneous imaging of pulmonary structure and regional function in patients with LAM.

School-age structural and functional MRI and lung function in children following lung resection for congenital lung malformation in infancy

BACKGROUND

The management of asymptomatic congenital lung malformations is debated. Particularly, there is a lack of information regarding long-term growth and development of the remaining lung in children following lung resection for congenital lung malformations. In addition to conventional pulmonary function tests, we used novel functional magnetic resonance imaging (MRI) methods to measure perfusion and ventilation.

OBJECTIVE

To assess functionality of the remaining lung expanded into the thoracic cavity after resection of congenital lung malformations.

MATERIALS AND METHODS

A prospective, cross-sectional pilot study in five children who had surgery for congenital lung malformations during infancy. Participants had structural and functional MRI as well as spirometry, body plethysmography and multiple breath washout at school age.

RESULTS

Structural MRI showed an expansion of the remaining lung in all cases. Fractional ventilation and relative perfusion of the expanded lung were locally decreased in functional MRI. In all other parts of the lungs, fractional ventilation and relative perfusion were normal in all children. There was an association between overall impairment of perfusion and elevated lung clearance index. The results of spirometry and body plethysmography varied between patients, including normal lung function, restriction and obstruction.

CONCLUSION

Fractional ventilation and relative perfusion maps from functional MRI specifically locate impairment of the remaining lung after lung resection. These changes are not captured by conventional measures such as structural MRI and standard pulmonary function tests. Therefore, following lung resection for congenital lung malformation, children should be investigated more systematically with functional lung MRI.

Ventilatory efficiency and its clinical and prognostic value in adults with cystic fibrosis

Cystic fibrosis, due to the absence or abnormal function of the cystic fibrosis transmembrane conductance regulator, is the most common life-limiting autosomal recessive genetic disorder among the Caucasian population. The lungs are particularly affected due to thick and tenacious mucus causing parenchymal anomalies ranging from bronchiectasis, progressive airflow limitation, respiratory infections, lung destruction and ultimately respiratory failure. Despite the remarkable advances in treatment that have greatly improved survival, most patients experience progressive exercise curtailment, with the consequence that a growing number of patients with cystic fibrosis will be referred for exercise-based evaluations in the forthcoming years. Cardiopulmonary exercise testing, in particular, is a useful tool to assess the mechanisms of exercise intolerance in individual patients that may have treatment and prognostic implications. In this review, we will focus on ventilatory efficiency and its clinical and prognostic value in adults with cystic fibrosis.

Effect of Salbutamol on Lung Ventilation in Children with Cystic Fibrosis: Comprehensive Assessment Using Spirometry, Multiple-Breath Washout, and Functional Lung Magnetic Resonance Imaging

BACKGROUND

Inhalation therapy is one of the cornerstones of the daily treatment regimen in patients with cystic fibrosis (CF). Recommendations regarding the addition of bronchodilators, especially salbutamol are conflicting due to the lack of evidence. New diagnostic measures such as multiple-breath washout (<underline>MBW)</underline> and functional magnetic resonance imaging (MRI) have the potential to reveal new insights into bronchodilator effects in patients with CF.

OBJECTIVE

The objective of the study was to comprehensively assess the functional response to nebulized inhalation with salbutamol in children with CF.

METHODS

Thirty children aged 6-18 years with stable CF performed pulmonary function tests, MBW, and matrix pencil-MRI before and after standardized nebulized inhalation of salbutamol.

RESULTS

Lung clearance index decreased (improved) by -0.24 turnover (95% confidence interval [CI]: -0.53 to 0.06; p = 0.111). Percentage of the lung volume with impaired fractional ventilation and relative perfusion decreased (improved) by -0.79% (CI: -1.99 to 0.42; p = 0.194) and -1.31% (CI: -2.28 to -0.35; p = 0.009), respectively. Forced expiratory volume (FEV1) increased (improved) by 0.41 z-score (CI: 0.24-0.58; p < 0.0001). We could not identify specific clinical factors associated with a more pronounced effect of salbutamol.

CONCLUSIONS

There is a positive short-term effect of bronchodilator inhalation on FEV1 in patients with CF, which is independent of ventilation inhomogeneity. Heterogeneous response between patients suggests that for prediction of a therapeutic effect this should be tested by spirometry in every patient individually.

Defect distribution index: A novel metric for functional lung MRI in cystic fibrosis

Purpose

Lung impairment from functional MRI is frequently assessed as defect percentage. The defect distribution, however, is currently not quantified. The purpose of this work was to develop a novel measure that quantifies how clustered or scattered defects in functional lung MRI appear, and to evaluate it in pediatric cystic fibrosis.

Theory

The defect distribution index (DDI) calculates a score for each lung voxel categorized as defected. The index increases according to how densely and how far an expanding circle around a defect voxel contains more than 50% defect voxels.

Methods

Fractional ventilation and perfusion maps of 53 children with cystic fibrosis were previously acquired with matrix pencil decomposition MRI. In this work, the DDI is compared to a visual score of 3 raters who evaluated how clustered the lung defects appear. Further, spearman correlations between DDI and lung function parameters were determined.

Results

The DDI strongly correlates with the visual scoring (r = 0.90 for ventilation; r = 0.88 for perfusion; P < .0001). Although correlations between DDI and defect percentage are moderate to strong (r = 0.61 for ventilation; r = 0.75 for perfusion; P < .0001), the DDI distinguishes between patients with comparable defect percentage.

Conclusion

The DDI is a novel measure for functional lung MRI. It provides complementary information to the defect percentage because the DDI assesses defect distribution rather than defect size. The DDI is applicable to matrix pencil MRI data of cystic fibrosis patients and shows very good agreement with human perception of defect distributions.

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Longitudinal course of clinical lung clearance index in children with cystic fibrosis

BACKGROUND

Although the lung clearance index (LCI) is a sensitive marker of small airway disease in individuals with cystic fibrosis (CF), less is known about longitudinal changes in LCI during routine clinical surveillance. Here, our objectives were to describe the longitudinal course of LCI in children with CF during routine clinical surveillance and assess influencing factors.

METHODS

Children with CF aged 3-18 years performed LCI measurements every 3 months as part of routine clinical care between 2011 and 2018. We recorded clinical data at every visit. We used a multilevel mixed effect model to determine changes in LCI over time and identify clinical factors that influence LCI course.

RESULTS

We collected LCI measurements from 1204 visits (3603 trials) in 78 participants, of which 907 visits had acceptable LCI data. The average unadjusted increase in LCI for the entire population was 0.29 (95% CI 0.20-0.38) LCI units·year^-1. The increase in LCI was more pronounced in adolescence (0.41 (95% CI 0.27-0.54) LCI units·year^-1). Colonisation with either Pseudomonas aeruginosa or Aspergillus fumigatus, pulmonary exacerbations, CF-related diabetes and bronchopulmonary aspergillosis were associated with a higher increase in LCI over time. Adjusting for clinical risk factors reduced the increase in LCI over time to 0.24 (95% CI 0.16-0.33) LCI units·year^-1.

CONCLUSIONS

LCI measured during routine clinical surveillance is associated with underlying disease progression in children with CF. An increased change in LCI over time should prompt further diagnostic intervention.

Time to get serious about the detection and monitoring of early lung disease in cystic fibrosis

Structural and functional defects within the lungs of children with cystic fibrosis (CF) are detectable soon after birth and progress throughout preschool years often without overt clinical signs or symptoms. By school age, most children have structural changes such as bronchiectasis or gas trapping/hypoperfusion and lung function abnormalities that persist into later life. Despite improved survival, gains in forced expiratory volume in one second (FEV₁) achieved across successive birth cohorts during childhood have plateaued, and rates of FEV₁ decline in adolescence and adulthood have not slowed. This suggests that interventions aimed at preventing lung disease should be targeted to mild disease and commence in early life. Spirometry-based classifications of 'normal' (FEV₁≥90% predicted) and 'mild lung disease' (FEV₁ 70%-89% predicted) are inappropriate, given the failure of spirometry to detect significant structural or functional abnormalities shown by more sensitive imaging and lung function techniques. The state and readiness of two imaging (CT and MRI) and two functional (multiple breath washout and oscillometry) tools for the detection and monitoring of early lung disease in children and adults with CF are discussed in this article.Prospective research programmes and technological advances in these techniques mean that well-designed interventional trials in early lung disease, particularly in young children and infants, are possible. Age appropriate, randomised controlled trials are critical to determine the safety, efficacy and best use of new therapies in young children. Regulatory bodies continue to approve medications in young children based on safety data alone and extrapolation of efficacy results from older age groups. Harnessing the complementary information from structural and functional tools, with measures of inflammation and infection, will significantly advance our understanding of early CF lung disease pathophysiology and responses to therapy. Defining clinical utility for these novel techniques will require effective collaboration across multiple disciplines to address important remaining research questions. Future impact on existing management burden for patients with CF and their family must be considered, assessed and minimised.To address the possible role of these techniques in early lung disease, a meeting of international leaders and experts in the field was convened in August 2019 at the Australiasian Cystic Fibrosis Conference. The meeting entitiled 'Shaping imaging and functional testing for early disease detection of lung disease in Cystic Fibrosis', was attended by representatives across the range of disciplines involved in modern CF care. This document summarises the proceedings, key priorities and important research questions highlighted.

Novel imaging techniques for cystic fibrosis lung disease

With an increasing number of patients with cystic fibrosis (CF) receiving highly effective CFTR (cystic fibrosis transmembrane regulator protein) modulator therapy, particularly at a young age, there is an increasing need to identify imaging tools that can detect and regionally visualize mild CF lung disease and subtle changes in disease state. In this review, we discuss the latest developments in imaging modalities for both structural and functional imaging of the lung available to CF clinicians and researchers, from the widely available, clinically utilized imaging methods for assessing CF lung disease-chest radiography and computed tomography-to newer techniques poised to become the next phase of clinical tools-structural/functional proton and hyperpolarized gas magnetic resonance imaging (MRI). Finally, we provide a brief discussion of several newer lung imaging techniques that are currently available only in selected research settings, including chest tomosynthesis, and fluorinated gas MRI. We provide an update on the clinical and/or research status of each technique, with a focus on sensitivity, early disease detection, and possibilities for monitoring treatment efficacy.

Lung clearance index predicts pulmonary exacerbations in individuals with primary ciliary dyskinesia: a multicentre cohort study

BACKGROUND

Lung clearance index (LCI) is a promising lung function outcome in individuals with primary ciliary dyskinesia (PCD). The impact of events clinically important for individuals with PCD, such as pulmonary exacerbations, on LCI is unknown.

METHODS

We conducted an international, multicentre, observational cohort study to assess the association of LCI and risk of pulmonary exacerbation, specific changes in LCI during pulmonary exacerbation and global variability of LCI across four visits every 4 months. Ninety individuals with PCD, aged 3-41 years, underwent nitrogen multiple-breath washout (MBW) and spirometry measurements. The association of LCI and pulmonary exacerbations was assessed by Cox proportional hazards and random-effects regression models.

RESULTS

We obtained 430 MBW and 427 spirometry measurements. In total, 379 person-years at risk contributed to the analysis. Per one unit increase (deterioration) in LCI, the risk of future pulmonary exacerbation increased by 13%: HR (95% CI), 1.13 (1.04 to 1.23). If LCI changed from a range of values considered normal to abnormal, the risk of future pulmonary exacerbations increased by 87%: 1.87 (1.08 to 3.23). During pulmonary exacerbations, LCI increased by 1.22 units (14.5%). After pulmonary exacerbations, LCI tended to decline. Estimates of variability in LCI suggested lower variation within individuals compared with variation between individuals. Findings were comparable for forced expiratory volume in 1 s.

CONCLUSION

On a visit-to-visit basis, LCI measurement may add to the prediction of pulmonary exacerbations, the assessment of lung function decline and the potential lung function response to treatment of pulmonary exacerbations.

Toward the Establishment of New Clinical Endpoints for Cystic Fibrosis: The Role of Lung Clearance Index and Cardiopulmonary Exercise Testing

As Cystic Fibrosis (CF) treatment advances, research evidence has highlighted the value and applicability of Lung Clearance Index and Cardiopulmonary Exercise Testing as endpoints for clinical trials. In the context of these new endpoints for CF trials, we have explored the use of these two test outcomes for routine CF care. In this review we have presented the use of these methods in assessing disease severity, disease progression, and the efficacy of new interventions with considerations for future research.

Current state of the art MRI for the longitudinal assessment of cystic fibrosis

Pulmonary MRI can now provide high-resolution images that are sensitive to early disease and specific to inflammation in cystic fibrosis (CF) lung disease. With specificity and function limited via computed tomography (CT), there are significant advantages to MRI. Many of the modern MRI techniques can be performed throughout life, and can be employed to understand changes over time, in addition to quantification of treatment response. Proton density and T1 /T2 contrast images can be obtained within a single breath-hold, providing depiction of structural abnormalities and active inflammation. Modern radial and/or spiral ultrashort echo-time (UTE) techniques rival CT in resolution for depiction and quantification of structure, for both airway and parenchymal abnormalities. Contrast perfusion MRI techniques are now utilized routinely to visualize changes in pulmonary and bronchial circulation that routinely occur in CF lung disease, and noncontrast techniques are moving closer to clinical translation. Functional information can be obtained from noncontrast proton images alone, using techniques such as Fourier decomposition. Hyperpolarized-gas MRI, increasingly using 129 Xe, is now becoming more widespread and has been demonstrated to have high sensitivity to early airway obstruction in CF via ventilation MRI. The sensitivity of 129 Xe MRI promises future use in personalized medicine, management of early CF lung disease, and in future clinical trials. By combining structural and functional techniques, with or without hyperpolarized gases, regional structure-function relationships can be obtained, giving insight into the pathophysiology of disease and improved clinical management. This article reviews the modern MRI techniques that can routinely be employed for CF lung disease in nearly any large medical center. Level of Evidence: 4 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2019.

[Assessment of lung impairment in patients with cystic fibrosis : Novel magnetic resonance imaging methods]

CLINICAL/METHODOLOGICAL ISSUE

The differentiated assessment of respiratory mechanics, gas exchange and pulmonary circulation, as well as structural impairment of the lung are essential for the treatment of patients with cystic fibrosis (CF). Clinical lung function measurements are often not sufficiently specific and are often difficult to perform.

STANDARD RADIOLOGICAL METHODS

The standard procedures for pulmonary imaging are chest X‑ray and computed tomography (CT) for assessing lung morphology. In more recent studies, an increasing number of centers are using magnetic resonance imaging (MRI) to assess lung structure and function. However, functional imaging is currently limited to specialized centers.

METHODOLOGICAL INNOVATIONS

In patients with CF, studies showed that MRI with hyperpolarized gases and Fourier decomposition/matrix pencil MRI (FD/MP-MRI) are feasible for assessing pulmonary ventilation. For pulmonary perfusion, dynamic contrast-enhanced MRI (DCE-MRI) or contrast-free methods, e.g., FD-MRI, can be used.

PERFORMANCE

Functional MRI provides more accurate insight into the pathophysiology of pulmonary function at the regional level. Advantages of MRI over X‑ray are its lack of ionizing radiation, the large number of lung function parameters that can be extracted using different contrast mechanisms, and ability to be used repeatedly over time.

ACHIEVEMENTS

Early assessment of lung function impairment is needed as the structural changes usually occur later in the course of the disease. However, sufficient experience in clinical application exist only for certain functional lung MRI procedures.

PRACTICAL RECOMMENDATIONS

Clinical application of the aforementioned techniques, except for DCE-MRI, should be restricted to scientific studies.

The impact of segmentation on whole-lung functional MRI quantification: Repeatability and reproducibility from multiple human observers and an artificial neural network

PURPOSE

To investigate the repeatability and reproducibility of lung segmentation and their impact on the quantitative outcomes from functional pulmonary MRI. Additionally, to validate an artificial neural network (ANN) to accelerate whole-lung quantification.

METHOD

Ten healthy children and 25 children with cystic fibrosis underwent matrix pencil decomposition MRI (MP-MRI). Impaired relative fractional ventilation (R_FV ) and relative perfusion (R_Q ) from MP-MRI were compared using whole-lung segmentation performed by a physician at two time-points (A_t1 and A_t2 ), by an MRI technician (B), and by an ANN (C). Repeatability and reproducibility were assess with Dice similarity coefficient (DSC), paired t-test and Intraclass-correlation coefficient (ICC).

RESULTS

The repeatability within an observer (A_t1 vs A_t2 ) resulted in a DSC of 0.94 ± 0.01 (mean ± SD) and an unsystematic difference of -0.01% for R_FV (P = .92) and +0.1% for R_Q (P = .21). The reproducibility between human observers (A_t1 vs B) resulted in a DSC of 0.88 ± 0.02, and a systematic absolute difference of -0.81% (P < .001) for R_FV and -0.38% (P = .037) for R_Q . The reproducibility between human and the ANN (A_t1 vs C) resulted in a DSC of 0.89 ± 0.03 and a systematic absolute difference of -0.36% for R_FV (P = .017) and -0.35% for R_Q (P = .002). The ICC was >0.98 for all variables and comparisons.

CONCLUSIONS

Despite high overall agreement, there were systematic differences in lung segmentation between observers. This needs to be considered for longitudinal studies and could be overcome by using an ANN, which performs as good as human observers and fully automatizes MP-MRI post-processing.

The assessment of short and long term changes in lung function in CF using 129Xe MRI

INTRODUCTION

129Xe ventilation MRI is sensitive to detect early CF lung disease and response to treatment. 129Xe-MRI could play a significant role in clinical trials and patient management. Here we present data on the repeatability of imaging measurements and their sensitivity to longitudinal change.

METHODS

29 children and adults with CF and a range of disease severity were assessed twice, a median [IQR] of 16.0 [14.4,19.5] months apart. Patients performed 129Xe-MRI, lung clearance index (LCI), body plethysmography and spirometry at both visits. Eleven patients repeated 129Xe-MRI in the same session to assess the within-visit repeatability. The ventilation defect percentage (VDP) was the primary metric calculated from 129Xe-MRI.

RESULTS

At baseline, mean (sd) age=23.0 (11.1) years and FEV1 z-score=-2.2 (2.0). Median [IQR] VDP=9.5 [3.4,31.6]%, LCI=9.0 [7.7,13.7]. Within-visit and inter-visit repeatability of VDP was high. At 16 months there was no single trend of 129Xe-MRI disease progression. Visible 129Xe-MRI ventilation changes were common, which reflected changes in VDP. Based on the within-visit repeatability, a significant short-term change in VDP is >±1.6%. For longer-term follow up, changes in VDP of up to ±7.7% can be expected, or ±4.1% for patients with normal FEV1. No patient had a significant change in FEV1, however 59% had change in VDP >±1.6%. In patients with normal FEV1, there were significant changes in ventilation and in VDP.

CONCLUSIONS

129Xe-MRI is a highly effective method for assessing longitudinal lung disease in patients with CF. VDP has great potential as a sensitive clinical outcome measure of lung function and endpoint for clinical trials.

The current status and further prospects for lung magnetic resonance imaging in pediatric radiology

Lung MRI makes it possible to replace up to 90% of CT examinations with radiation-free magnetic resonance diagnostics of the lungs without suffering any diagnostic loss. The individual radiation exposure can thus be relevantly reduced. This applies in particular to children who repeatedly require sectional imaging of the lung, e.g., in tumor surveillance or in chronic lung diseases such as cystic fibrosis. In this paper we discuss various factors that favor the establishment of lung MRI in the clinical setting. Among the many sequences proposed for lung imaging, respiration-triggered T2-W turbo spin-echo (TSE) sequences have been established as a good standard for children. Additional sequences are mostly dispensable. The most important pulmonary findings are demonstrated here in the form of a detailed pictorial essay. T1-weighted gradient echo sequences with ultrashort echo time are a new option. These sequences anticipate signal loss in the lung and deliver CT-like images with high spatial resolution. When using self-gated T1-W ultrashort echo time 3-D sequences that acquire iso-voxel geometry in the sub-millimeter range, secondary reconstructions are possible.

A multi-scale model of gas transport in the lung to study heterogeneous lung ventilation during the multiple-breath washout test

The multiple-breath washout (MBW) is a lung function test that measures the degree of ventilation inhomogeneity (VI). The test is used to identify small airway impairment in patients with lung diseases like cystic fibrosis. However, the physical and physiological factors that influence the test outcomes and differentiate health from disease are not well understood. Computational models have been used to better understand the interaction between anatomical structure and physiological properties of the lung, but none of them has dealt in depth with the tracer gas washout test in a whole. Thus, our aim was to create a lung model that simulates the entire MBW and investigate the role of lung morphology and tissue mechanics on the tracer gas washout procedure. To this end, we developed a multi-scale lung model to simulate the inert gas transport in airways of all size. We then applied systematically different modifications to geometrical and mechanical properties of the lung model (compliance, residual airway volume and flow resistance) which have been associated with VI. The modifications were applied to distinct parts of the model, and their effects on the gas distribution within the lung and on the gas concentration profile were assessed. We found that variability in compliance and residual volume of the airways, as well as the spatial distribution of this variability in the lung had a direct influence on gas distribution among airways and on the MBW pattern (washout duration, characteristic concentration profile during each expiration), while the effects of variable flow resistance were negligible. Based on these findings, it is possible to classify different types of inhomogeneities in the lung and relate them to specific features of the MBW pattern, which builds the basis for a more detailed association of lung function and structure.

Obstructive lung diseases, like cystic fibrosis or primary ciliary dyskinesia, lead to inhomogeneous ventilation. The degree of observed inhomogeneity represents a clinical measure for the progression of the disease. The multiple-breath washout (MBW) is a lung function test that measures this inhomogeneity in the lung. However, the factors that influence the results of the test and differentiate between health and disease are not well understood. Computational models help us to understand better the relation between anatomical structure and physiological properties of the lung, but none of them has dealt in depth with the MBW test in whole. Our aim was to create a lung model that simulates the entire MBW test and study the role of lung structure and tissue mechanics on the washout procedure. We developed a multi-scale lung model to simulate the inert gas transport in all airways including the gas exchange area. Our model offers the opportunity to understand the ventilation distribution in the healthy lung. It can also mimic certain patterns of lung disease by applying modifications in mechanical properties out of the physiological limits. Thus, it can be used to study MBW characteristics in health and disease.

Within-breath changes in respiratory system impedance in children with cystic fibrosis

BACKGROUND

The aim of this study was to assess within-breath respiratory system impedance by the forced oscillation technique (FOT) in children with cystic fibrosis (CF) and relate it to the underlying lung disease.

METHODS

Thirty-three children with CF (median [range] age 12.0 [6-17] years) underwent FOT at 8 Hz during tidal breathing, multiple breath nitrogen washout (LCI), spirometry (FEV1), body plethysmography (RV/TLC), and magnetic resonance imaging (MRI). FOT outcomes included: mean inspiratory, expiratory, and whole breath resistance (R8_INSP , R8_EXP , R8_TOT ) and reactance (X8_INSP , X8_EXP , X8_TOT ), and the differences between X8_INSP and X8_EXP (ΔX8). Morphological changes were evaluated by MRI using CF-specific morphological scores. Spearman correlation was performed to examine the correlation between FOT indices and other parameters.

RESULTS

FEV1 was negatively correlated with R8_EXP (r = -0.52, P = 0.002) and ΔX8 (r = -0.55, P = 0.001), and positively correlated with and X8_EXP (r = 0.56, P < 0.001). RV/TLC was positively correlated with R8_EXP (r = 0.43, P = 0.013), and ΔX8 (r = 0.54, P = 0.001) and negatively correlated with X8_EXP (r = -0.54, P = 0.001). We found poor correlation between FOT parameters and LCI and no correlation between FOT parameters and MRI scores.

CONCLUSION

In children with CF, changes in within-breath FOT parameters are consistent with peripheral obstruction and dynamic airway compression, while they are not associated with ventilation heterogeneities and morphological alterations.

Free-breathing quantification of regional ventilation derived by phase-resolved functional lung (PREFUL) MRI

PURPOSE

To test the feasibility of regional fully quantitative ventilation measurement in free breathing derived by phase-resolved functional lung (PREFUL) MRI in the supine and prone positions. In addition, the influence of T₂ * relaxation time on ventilation quantification is assessed.

METHODS

Twelve healthy volunteers underwent functional MRI at 1.5 T using a 2D triple-echo spoiled gradient echo sequence allowing for quantitative measurement of T₂ * relaxation time. Minute ventilation (ΔV) was quantified by conventional fractional ventilation (FV) and the newly introduced regional ventilation (VR), which corrects volume errors due to image registration. ΔV_FV versus ΔV_VR and ΔV_VR versus ΔV_VR with T₂ * correction were compared using Bland-Altman plots and correlation analysis. The repeatability and physiological plausibility of all measurements were tested in the supine and prone positions.

RESULTS

On global and regional scales a strong correlation was observed between ΔV_FV versus ΔV_VR and ΔV_VR versus ΔV_VRT2* (r > 0.93); however, regional Bland-Altman analysis showed systematic differences (p < 0.0001). Unlike ΔV_VRT2* , ΔV_VR and ΔV_FV showed expected physiologic anterior-posterior gradients, which decreased in the supine but not in the prone position at second measurement during 3 min in the same position. For all quantification methods a moderate repeatability (coefficient of variation <20%) of ventilation was found.

CONCLUSION

A fully quantified regional ventilation measurement using ΔV_VR in free breathing is feasible and shows physiologically plausible results. In contrast to conventional ΔV_FV, volume errors due to image registration are eliminated with the ΔV_VR approach. However, correction for the T₂ * effect remains challenging.

Quantitative multivolume proton-magnetic resonance imaging in patients with cystic fibrosis lung disease: comparison with clinical indicators

This cross-sectional study aims to verify the relationship between quantitative multivolume proton-magnetic resonance imaging (¹H-MRI) and clinical indicators of ventilatory abnormalities in cystic fibrosis (CF) lung disease.Non-enhanced chest MRI, spirometry and multiple breath washout was performed by 28 patients (10-27 years) with CF lung disease. Images acquired at end-inspiration and end-expiration were registered by optical flow to estimate expiratory-inspiratory proton-density change (Δ¹H-MRI) as a measure of regional ventilation. Magnetic resonance images were also evaluated using a CF-specific scoring system.Biomarkers of CF ventilation impairment were defined from the Δ¹H-MRI as follows: Δ¹H-MRI median, Δ¹H-MRI quartile coefficient of variation (QCV) and percentage of low-ventilation volume (%LVV). Imaging biomarkers correlated to all the clinical measures of ventilation abnormality, with the strongest correlation between Δ¹H-MRI median and forced expiratory volume in 1 s (r²=0.44, p<0.001), Δ¹H-MRI QCV and lung clearance index (LCI) (r²=0.51, p<0.001) and %LVV and LCI (r²=0.66, p<0.001). Correlations were also found between imaging biomarkers of ventilation and morphological scoring.The study showed a significant correlation between quantitative multivolume MRI and clinical indicators of CF lung disease. MRI, as a non-ionising imaging technique, may be particularly attractive in CF care for longitudinal evaluation, providing a new imaging biomarker to detect early ventilatory abnormalities.

Single-breath washout and association with structural lung disease in children with cystic fibrosis

BACKGROUND

In children with cystic fibrosis (CF) lung clearance index (LCI) from multiple-breath washout (MBW) correlates with structural lung disease. As a shorter test, single-breath washout (SBW) represents an attractive alternative to assess the ventilation distribution, however, data for the correlation with lung imaging are lacking.

METHODS

We assessed correlations between phase III slope (SIII) of double-tracer gas SBW, nitrogen MBW indices (LCI and moment ratios for overall ventilation distribution, Scond, and Sacin for conductive and mainly acinar ventilation, respectively) and structural lung disease assessed by chest computed tomography (CT) in children with CF.

RESULTS

In a prospective cross-sectional study data from MBW, SBW, and chest CT were obtained in 32 children with CF with a median (range) age of 8.2 (5.2-16.3) years. Bronchiectasis was present in 24 (75%) children and air trapping was present in 29 (91%). Median (IQR) SIII of SBW was -138.4 (150.6) mg/mol. We found no association between SIII with either the MBW outcomes or CT scores (n = 23, association with bronchiectasis extent r = 0.10, P = 0.64). LCI and Scond were associated with bronchiectasis extent (n = 23, r = 0.57, P = 0.004; r = 0.60, P = 0.003, respectively).

CONCLUSIONS

Acinar ventilation inhomogeneity measured by SBW was not associated with structural lung disease on CT. Double-tracer SBW added no benefit to indices measured by MBW.

Ventilation and perfusion assessed by functional MRI in children with CF: reproducibility in comparison to lung function

BACKGROUND

Chronic lung diseases such as cystic fibrosis (CF) can be monitored by imaging and lung function modalities. Magnetic resonance imaging (MRI) techniques such as matrix pencil (MP) decomposition allows for evaluation of regional impairment of fractional ventilation (R_FV) and relative perfusion (R_Q). However, reproducibility of MP MRI outcomes in children with CF is unknown. We examined short-term variability of ventilation and perfusion impairment from MP MRI and compared this to lung function outcomes.

METHOD

Twenty-threeCF and 12 healthy school-aged children underwent MRI and lung function tests on the same day on two occasions 24 h apart. Global ventilation inhomogeneity was assessed by the lung clearance index (LCI) from nitrogen-multiple breath washout (N₂-MBW) technique. Intra-class-coefficient (ICC), percentage change, and Bland-Altman limits of agreement were evaluated to assess reproducibility.

RESULTS

Sixty-nine measurements from MP MRI and N₂-MBW were performed. The ICC between two visits for R_FV, R_Q and LCI ranged between 0.60 and 0.90 in individuals with CF and healthy controls. In individuals with CF, percentage of change between the visits was 0.02% for R_FV, -1.11% for R_Q and 2.91% for LCI and limits of agreement between visits were - 4.3% and 3.9% for R_FV, -4.4% and 3.7% for R_Q, and -2.6 and 3.0 for LCI.

CONCLUSIONS

Functional imaging is reproducible and short-term changes in R_FV and R_Q greater than ±4.4% can be considered clinical meaningful. Very good short-term reproducibility, and easy application without the need for breathing maneuvers or contrast agent, makes MP MRI a promising surveillance method for CF.