MRI-derived regional flow-volume loop parameters detect early-stage chronic lung allograft dysfunction

Free-breathing 3D phase-resolved functional lung MRI vs breath-hold hyperpolarized 129Xe ventilation MRI in patients with chronic obstructive pulmonary disease and healthy volunteers

OBJECTIVES

3D phase-resolved functional lung (PREFUL) MRI offers evaluation of pulmonary ventilation without inhalation of contrast agent. This study seeks to compare ventilation maps obtained from 3D PREFUL MRI with a direct ventilation measurement derived from 129Xe MRI in both patients with chronic obstructive pulmonary disease (COPD) and healthy volunteers.

METHODS

Thirty-one patients with COPD and 12 healthy controls underwent free-breathing 3D PREFUL MRI and breath-hold 129Xe MRI at 1.5 T. For both MRI techniques, ventilation defect (VD) maps were determined and respective ventilation defect percentage (VDP) values were computed. All parameters of both techniques were compared by Spearman correlation coefficient (r) and the differences between VDP values were quantified by Bland-Altman analysis and tested for significance using Wilcoxon signed-rank test. In a regional comparison of VD maps, spatial overlap and Sørensen-Dice coefficients of healthy and defect areas were computed.

RESULTS

On a global level, all 3D PREFUL VDP values correlated significantly to VDP measure derived by 129Xe ventilation imaging (all r > 0.65; all p < 0.0001). 129Xe VDP was significantly greater than 3D PREFUL derived VDPRVent (mean bias = 10.5%, p < 0.001) and VDPFVL-CM (mean bias = 11.3%, p < 0.0001) but not for VDPCombined (mean bias = 1.7%, p = 0.70). The total regional agreement of 129Xe and 3D PREFUL VD maps ranged between 60% and 63%.

CONCLUSIONS

Free-breathing 3D PREFUL MRI showed a strong correlation with breath-hold hyperpolarized 129Xe MRI regarding the VDP values and modest differences in the detection of VDs on a regional level.

CLINICAL RELEVANCE STATEMENT

3D PREFUL MRI correlated with 129Xe MRI, unveiling regional differences in COPD defect identification. This proposes 3D PREFUL MRI as a ventilation mapping surrogate, eliminating the need for extra hardware or inhaled gases.

KEY POINTS

Current non-invasive evaluation techniques for lung diseases have drawbacks; 129Xe MRI is limited by cost and availability. 3D PREFUL MRI correlated with 129Xe MRI, with regional differences in identifying COPD defects. 3D PREFUL MRI can provide ventilation mapping without the need for additional hardware or inhaled gases.

Multicenter Standardization of Phase-Resolved Functional Lung MRI in Patients With Suspected Chronic Thromboembolic Pulmonary Hypertension

BACKGROUND

Detection of pulmonary perfusion defects is the recommended approach for diagnosing chronic thromboembolic pulmonary hypertension (CTEPH). This is currently achieved in a clinical setting using scintigraphy. Phase-resolved functional lung (PREFUL) magnetic resonance imaging (MRI) is an alternative technique for evaluating regional ventilation and perfusion without the use of ionizing radiation or contrast media.

PURPOSE

To assess the feasibility and image quality of PREFUL-MRI in a multicenter setting in suspected CTEPH.

STUDY TYPE

This is a prospective cohort sub-study.

POPULATION

Forty-five patients (64 ± 16 years old) with suspected CTEPH from nine study centers.

FIELD STRENGTH/SEQUENCE

1.5 T and 3 T/2D spoiled gradient echo/bSSFP/T2 HASTE/3D MR angiography (TWIST).

ASSESSMENT

Lung signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were compared between study centers with different MRI machines. The contrast between normally and poorly perfused lung areas was examined on PREFUL images. The perfusion defect percentage calculated using PREFUL-MRI (QDPPREFUL) was compared to QDP from the established dynamic contrast-enhanced MRI technique (QDPDCE). Furthermore, QDPPREFUL was compared between a patient subgroup with confirmed CTEPH or chronic thromboembolic disease (CTED) to other clinical subgroups.

STATISTICAL TESTS

t-Test, one-way analysis of variance (ANOVA), Pearson's correlation. Significance level was 5%.

RESULTS

Significant differences in lung SNR and CNR were present between study centers. However, PREFUL perfusion images showed a significant contrast between normally and poorly perfused lung areas (mean delta of normalized perfusion -4.2% SD 3.3) with no differences between study sites (ANOVA: P = 0.065). QDPPREFUL was significantly correlated with QDPDCE (r = 0.66), and was significantly higher in 18 patients with confirmed CTEPH or CTED (57.9 ± 12.2%) compared to subgroups with other causes of PH or with excluded PH (in total 27 patients with mean ± SD QDPPREFUL = 33.9 ± 17.2%).

DATA CONCLUSION

PREFUL-MRI could be considered as a non-invasive method for imaging regional lung perfusion in multicenter studies.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 1.

Free-Breathing Functional Pulmonary Proton MRI: A Novel Approach Using Voxel-Wise Lung Ventilation (VOLVE) Assessment in Healthy Volunteers and Patients With Chronic Obstructive Pulmonary Disease

BACKGROUND

In respiratory medicine, there is a need for sensitive measures of regional lung function that can be performed using standard imaging technology, without the need for inhaled or intravenous contrast agents.

PURPOSE

To describe VOxel-wise Lung VEntilation (VOLVE), a new method for quantifying regional lung ventilation (V) and perfusion (Q) using free-breathing proton MRI, and to evaluate VOLVE in healthy never-smokers, healthy people with smoking history, and people with chronic obstructive pulmonary disease (COPD).

STUDY TYPE

Prospective pilot.

POPULATION

Twelve healthy never-smoker participants (age 30.3 ± 12.5 years, five male), four healthy participants with smoking history (>10 pack-years) (age 42.5 ± 18.3 years, one male), and 12 participants with COPD (age 62.8 ± 11.1 years, seven male).

FIELD STRENGTH/SEQUENCE

Single-slice free-breathing two-dimensional fast field echo sequence at 3 T.

ASSESSMENT

A novel postprocessing was developed to evaluate the MR signal changes in the lung parenchyma using a linear regression-based approach, which makes use of all the data in the time series for maximum sensitivity. V/Q-weighted maps were produced by computing the cross-correlation, lag and gradient between the respiratory/cardiac phase time course and lung parenchyma signal time courses. A comparison of histogram median and skewness values and spirometry was performed.

STATISTICAL TESTS

Kruskal-Wallis tests with Dunn's multiple comparison tests to compare VOLVE metrics between groups; Spearman correlation to assess the correlation between MRI and spirometry-derived parameters; and Bland-Altman analysis and coefficient of variation to evaluate repeatability were used. A P-value <0.05 was considered significant.

RESULTS

Significant differences between the groups were found for ventilation between healthy never-smoker and COPD groups (median XCCV, LagV, and GradV) and perfusion (median XCCQ, LagQ, and GradQ). Minimal bias and no significant differences between intravisit scans were found (P range = 0.12-0.97).

DATA CONCLUSION

This preliminary study showed that VOLVE has potential to provide metrics of function quantification.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 1.

Estimating ventilation correlation coefficients in the lungs using PREFUL-MRI in chronic obstructive pulmonary disease patients and healthy adults

PURPOSE

Various parameters of regional lung ventilation can be estimated using phase-resolved functional lung (PREFUL)-MRI. The parameter "ventilation correlation coefficient (Vent-CC)" was shown advantageous because it assesses the dynamics of regional air flow. Calculating Vent-CC depends on a voxel-wise comparison to a healthy reference flow curve. This work examines the effect of placing a reference region of interest (ROI) in various lung quadrants or in different coronal slices. Furthermore, algorithms for automated ROI selection are presented and compared in terms of test-retest repeatability.

METHODS

Twenty-eight healthy subjects and 32 chronic obstructive pulmonary disease (COPD) patients were scanned twice using PREFUL-MRI. Retrospective analyses examined the homogeneity of air flow curves of various reference ROIs using cross-correlation. Vent-CC and ventilation defect percentage (VDP) calculated using various reference ROIs were compared using one-way analysis of variance (ANOVA). The coefficient of variation was calculated for Vent-CC and VDP when using different reference selection algorithms.

RESULTS

Flow-volume curves were highly correlated between ROIs placed at various lung quadrants in the same coronal slice (r > 0.97) with no differences in Vent-CC and VDP (ANOVA: p > 0.5). However, ROIs placed at different coronal slices showed lower correlation coefficients and resulted in significantly different Vent-CC and VDP values (ANOVA: p < 0.001). Vent-CC and VDP showed higher repeatability when calculated using the presented new algorithm.

CONCLUSION

In COPD and healthy cohorts, assessing regional ventilation dynamics using PREFUL-MRI in terms of the Vent-CC metric showed higher repeatability using a new algorithm for selecting a homogenous reference ROI from the same slice.

Phase-Resolved Functional Lung (PREFUL) MRI to Quantify Ventilation: Feasibility and Physiological Relevance in Severe Asthma

RATIONALE AND OBJECTIVES

Emergent evidence in several respiratory diseases supports translational potential for Phase-Resolved Functional Lung (PREFUL) MRI to spatially quantify ventilation but its feasibility and physiological relevance have not been demonstrated in patients with asthma. This study compares PREFUL-derived ventilation defect percent (VDP) in severe asthma patients to healthy controls and measures its responsiveness to bronchodilator therapy and relation to established measures of airways disease.

MATERIALS AND METHODS

Forty-one adults with severe asthma and seven healthy controls performed same-day free-breathing 1H MRI, 129Xe MRI, spirometry, and oscillometry. A subset of participants (n = 23) performed chest CT and another subset of participants with asthma (n = 19) repeated 1H MRI following the administration of a bronchodilator. VDP was calculated for both PREFUL and 129Xe MRI. Additionally, the percent of functional small airways disease was determined from CT parametric response maps (PRMfSAD).

RESULTS

PREFUL VDP measured pre-bronchodilator (19.1% [7.4-43.3], p = 0.0002) and post-bronchodilator (16.9% [6.1-38.4], p = 0.0007) were significantly greater than that of healthy controls (7.5% [3.7-15.5]) and was significantly decreased post-bronchodilator (from 21.9% [10.1-36.9] to 16.9% [6.1-38.4], p = 0.0053). PREFUL VDP was correlated with spirometry (FEV1%pred: r = -0.46, p = 0.0023; FVC%pred: r = -0.35, p = 0.024, FEV1/FVC: r = -0.46, p = 0.0028), 129Xe MRI VDP (r = 0.39, p = 0.013), and metrics of small airway disease (CT PRMfSAD: r = 0.55, p = 0.021; Xrs5 Hz: r = -0.44, p = 0.0046, and AX: r = 0.32, p = 0.044).

CONCLUSION

PREFUL-derived VDP is responsive to bronchodilator therapy in asthma and is associated with measures of airflow obstruction and small airway dysfunction. These findings validate PREFUL VDP as a physiologically relevant and accessible ventilation imaging outcome measure in asthma.

Comparison of Free-Breathing 3D Phase-Resolved Functional Lung (PREFUL) MRI With Dynamic 19 F Ventilation MRI in Patients With Obstructive Lung Disease and Healthy Volunteers

BACKGROUND

Non-contrast-enhanced 1 H magnetic resonance imaging (MRI) with full lung coverage shows promise for assessment of regional lung ventilation but a comparison with direct ventilation measurement using 19 F MRI is lacking.

PURPOSE

To compare ventilation parameters calculated using 3D phase-resolved functional lung (PREFUL) MRI with 19 F MRI.

STUDY TYPE

Prospective.

POPULATION

Fifteen patients with asthma, 14 patients with chronic obstructive lung disease, and 13 healthy volunteers.

FIELD STRENGTH/SEQUENCE

A 3D gradient-echo pulse sequence with golden-angle increment and stack-of-stars encoding at 1.5 T.

ASSESSMENT

All participants underwent 3D PREFUL MRI and 19 F MRI. For 3D PREFUL, static regional ventilation (RVent) and dynamic flow-volume cross-correlation metric (FVL-CM) were calculated. For both parameters, ventilation defect percentage (VDP) values and ventilation defect (VD) maps (including a combination of both parameters [VDPCombined ]) were determined. For 19 F MRI, images from eight consecutive breaths under volume-controlled inhalation of perfluoropropane were acquired. Time-to-fill (TTF) and wash-in (WI) parameters were extracted. For all 19 F parameters, a VD map was generated and the corresponding VDP values were calculated.

STATISTICAL TESTS

For all parameters, the relationship between the two techniques was assessed using a Spearman correlation (r). Differences between VDP values were compared using Bland-Altman analysis. For regional comparison of VD maps, spatial overlap and Sørensen-Dice coefficients were computed.

RESULTS

3D PREFUL VDP values were significantly correlated to VDP measures by 19 F (r range: 0.59-0.70). For VDPRVent , no significant bias was observed with VDP of the third and fourth breath (bias range = -6.8:7.7%, P range = 0.25:0.30). For VDPFVL-CM , no significant bias was found with VDP values of fourth-eighth breaths (bias range = -2.0:12.5%, P range = 0.12:0.75). The overall spatial overlap of all VD maps increased with each breath, ranging from 61% to 81%, stabilizing at the fourth breath.

DATA CONCLUSION

3D PREFUL MRI parameters showed moderate to strong correlation with 19 F MRI. Depending on the 3D PREFUL VD map, the best regional agreement was found to 19 F VD maps of third-fifth breath.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 2.

Inter- and intravisit repeatability of free-breathing MRI in pediatric cystic fibrosis lung disease

PURPOSE

The purpose of this study is to assess the intra- and interscan repeatability of free-breathing phase-resolved functional lung (PREFUL) MRI in stable pediatric cystic fibrosis (CF) lung disease in comparison to static breath-hold hyperpolarized 129-xenon MRI (Xe-MRI) and pulmonary function tests.

METHODS

Free-breathing 1-hydrogen MRI and Xe-MRI were acquired from 15 stable pediatric CF patients and seven healthy age-matched participants on two visits, 1 month apart. Same-visit MRI scans were also performed on a subgroup of the CF patients. Following the PREFUL algorithm, regional ventilation (RVent) and regional flow volume loop cross-correlation maps were determined from the free-breathing data. Ventilation defect percentage (VDP) was determined from RVent maps (VDP_RVent ), regional flow volume loop cross-correlation maps (VDP_CC ), VDP_RVent ∪ VDP_CC , and multi-slice Xe-MRI. Repeatability was evaluated using Bland-Altman analysis, coefficient of repeatability (CR), and intraclass correlation.

RESULTS

Minimal bias and no significant differences were reported for all PREFUL MRI and Xe-MRI VDP parameters between intra- and intervisits (all P > 0.05). Repeatability of VDP_RVent , VDP_CC , VDP_RVent ∪ VDP_CC , and multi-slice Xe-MRI were lower between the two-visit scans (CR = 14.81%, 15.36%, 16.19%, and 9.32%, respectively) in comparison to the same-day scans (CR = 3.38%, 2.90%, 1.90%, and 3.92%, respectively). pulmonary function tests showed high interscan repeatability relative to PREFUL MRI and Xe-MRI.

CONCLUSION

PREFUL MRI, similar to Xe-MRI, showed high intravisit repeatability but moderate intervisit repeatability in CF, which may be due to inherent disease instability, even in stable patients. Thus, PREFUL MRI may be considered a suitable outcome measure for future treatment response studies.

Functional lung imaging using novel and emerging MRI techniques

Respiratory diseases are leading causes of death and disability in the world. While early diagnosis is key, this has proven difficult due to the lack of sensitive and non-invasive tools. Computed tomography is regarded as the gold standard for structural lung imaging but lacks functional information and involves significant radiation exposure. Lung magnetic resonance imaging (MRI) has historically been challenging due to its short T2 and low proton density. Hyperpolarised gas MRI is an emerging technique that is able to overcome these difficulties, permitting the functional and microstructural evaluation of the lung. Other novel imaging techniques such as fluorinated gas MRI, oxygen-enhanced MRI, Fourier decomposition MRI and phase-resolved functional lung imaging can also be used to interrogate lung function though they are currently at varying stages of development. This article provides a clinically focused review of these contrast and non-contrast MR imaging techniques and their current applications in lung disease.

Evaluation of image registration algorithms for 3D phase-resolved functional lung ventilation magnetic resonance imaging in healthy volunteers and chronic obstructive pulmonary disease patients

The purpose of the current study was to assess the influence of the registration algorithms on the repeatability of three-dimensional (3D) phase-resolved functional lung (PREFUL) ventilation magnetic resonance imaging (MRI). Twenty-three healthy volunteers and 10 patients with chronic obstructive pulmonary disease (COPD) underwent 3D PREFUL MRI during tidal breathing. The registration of dynamically acquired data to a fixed image was executed using single-step, stepwise, and group-oriented registration (GOREG) approaches. Advanced Normalization Tools (ANTs) and the Forsberg image-registration package were used for the registration. Image registration algorithms were tested for differences and evaluated by the repeatability analysis of ventilation parameters using coefficient of variation (CoV), intraclass-correlation coefficient, Bland-Altman plots, and correlation to spirometry. Also, the registration time and image quality were computed for all registration approaches. Very strong to strong correlations (r range: 0.917-0.999) were observed between ventilation parameters derived using various registration approaches. Median CoV values of the cross-correlation (CC) parameter were significantly lower (all p ≤ 0.0054) for ANTs GOREG compared with single-step and stepwise ANTs registration. The majority of comparisons between COPD patients and age-matched healthy volunteers showed agreement among the registration approaches. The repeatability of regional ventilation (RVent)-based ventilation defect percentage (VDP_RVent ) and VDP_CC was significantly higher (both p ≤ 0.0054) for Forsberg GOREG compared with ANTs GOREG. All 3D PREFUL-derived ventilation parameters correlated with forced expiratory volume in 1 s (FEV₁ ) and the FEV₁ / forced vital capacity (FVC) ratio (all |r| > 0.40, all p < 0.03). The image sharpness of RVent maps was statistically elevated (all p < 0.001) using GOREG compared with single-step and stepwise registration approaches using ANTs. The best computational performance was achieved with Forsberg GOREG. The GOREG scheme improves the repeatability and image quality of dynamic 3D PREFUL ventilation parameters. Registration time can be ~10-fold reduced to 9 min using the Forsberg method with equal or even improved repeatability and comparable PREFUL ventilation results compared with the ANTs method.

Pulmonary Dysfunction after Pediatric COVID-19

Background Long COVID occurs at a lower frequency in children and adolescents than in adults. Morphologic and free-breathing phase-resolved functional low-field-strength MRI may help identify persistent pulmonary manifestations after SARS-CoV-2 infection. Purpose To characterize both morphologic and functional changes of lung parenchyma at low-field-strength MRI in children and adolescents with post-COVID-19 condition compared with healthy controls. Materials and Methods Between August and December 2021, a cross-sectional clinical trial using low-field-strength MRI was performed in children and adolescents from a single academic medical center. The primary outcome was the frequency of morphologic changes at MRI. Secondary outcomes included MRI-derived functional proton ventilation and perfusion parameters. Clinical symptoms, the duration from positive reverse transcriptase-polymerase chain reaction test result, and serologic parameters were compared with imaging results. Nonparametric tests for pairwise and corrected tests for groupwise comparisons were applied to assess differences in healthy controls, recovered participants, and those with long COVID. Results A total of 54 participants after COVID-19 infection (mean age, 11 years ± 3 [SD]; 30 boys [56%]) and nine healthy controls (mean age, 10 years ± 3; seven boys [78%]) were included: 29 (54%) in the COVID-19 group had recovered from infection and 25 (46%) were classified as having long COVID on the day of enrollment. Morphologic abnormality was identified in one recovered participant. Both ventilated and perfused lung parenchyma (ventilation-perfusion [V/Q] match) was higher in healthy controls (81% ± 6.1) compared with the recovered group (62% ± 19; P = .006) and the group with long COVID (60% ± 20; P = .003). V/Q match was lower in patients with time from COVID-19 infection to study participation of less than 180 days (63% ± 20; P = .03), 180-360 days (63% ± 18; P = .03), and 360 days (41% ± 12; P < .001) as compared with the never-infected healthy controls (81% ± 6.1). Conclusion Low-field-strength MRI showed persistent pulmonary dysfunction in children and adolescents who recovered from COVID-19 and those with long COVID. Clinical trial registration no. NCT04990531 © RSNA, 2022 Supplemental material is available for this article. See also the editorial by Paltiel in this issue.

Assessment of lung ventilation of premature infants with bronchopulmonary dysplasia at 1.5 Tesla using phase-resolved functional lung magnetic resonance imaging

BACKGROUND

The most common chronic complication of preterm birth is bronchopulmonary dysplasia (BPD), widely referred to as chronic lung disease of prematurity. All current definitions rely on characterizing the disease based on respiratory support level and do not provide full understanding of the underlying cardiopulmonary pathophysiology.

OBJECTIVE

To evaluate a rapid functional lung imaging technique in premature infants and to quantitate pulmonary ventilation using 1.5 Tesla magnetic resonance imaging (MRI).

MATERIALS AND METHODS

We conducted a prospective MRI study of 12 premature infants in the neonatal intensive care unit (NICU) using the phase resolved functional lung MRI technique to calculate pulmonary ventilation parameters in preterm infants with and without BPD grade 0/1 (n = 6) and grade 2/3 (n = 6).

RESULTS

The total ventilation defect percentage showed a significant difference between groups (16.0% IQR (11.0%,18%) BPD grade 2/3 vs. 8.0% IQR (4.5%,9.0%) BPD grade 0/1, p = 0.01).

CONCLUSION

Phase-resolved functional lung MRI is feasible for assessment of ventilation defect percentages in preterm infants and shows regional variation in localized lung function in this population.

Biomarkers for Chronic Lung Allograft Dysfunction: Ready for Prime Time?

Chronic lung allograft dysfunction (CLAD) remains a major hurdle impairing lung transplant outcome. Parallel to the better clinical identification and characterization of CLAD and CLAD phenotypes, there is an increasing urge to find adequate biomarkers that could assist in the earlier detection and differential diagnosis of CLAD phenotypes, as well as disease prognostication. The current status and state-of-the-art of biomarker research in CLAD will be discussed with a particular focus on radiological biomarkers or biomarkers found in peripheral tissue, bronchoalveolar lavage' and circulating blood' in which significant progress has been made over the last years. Ultimately, although a growing number of biomarkers are currently being embedded in the follow-up of lung transplant patients, it is clear that one size does not fit all. The future of biomarker research probably lies in the rigorous combination of clinical information with findings in tissue, bronchoalveolar lavage' or blood. Only by doing so, the ultimate goal of biomarker research can be achieved, which is the earlier identification of CLAD before its clinical manifestation. This is desperately needed to improve the prognosis of patients with CLAD after lung transplantation.

Monitoring practices of chronic lung allograft dysfunction in pediatric lung transplantation

INTRODUCTION

Chronic lung allograft dysfunction (CLAD) continues to negatively impact the survival of pediatric lung transplant (LTx) recipients. Current consensus guidelines are adult-focused. We sought to examine CLAD detection and monitoring practices at pediatric LTx programs.

METHODS

We conducted a survey among the International Pediatric Lung Transplant Collaborative. Questions consisted of practitioner's experience, LTx program demographics, and querying tests used for CLAD surveillance and detection. Investigations queried included: chest x-ray (CXR), chest computed tomography (CT), lung magnetic resonance imaging (MRI), ventilation/perfusion scanning, conventional pulmonary function testing (PFT), multiple breath washout (MBW), infant/preschool PFT, bronchoalveolar lavage, transbronchial biopsies (TBBx), or other tissue sampling techniques. Preferences for certain modalities over others were questioned based on a five-point Likert scale.

RESULTS

Twenty-four of 25 programs responded. Chest CT and CXR are used generally for both CLAD surveillance and detection. No programs use lung MRI clinically, it may have some utility in the future. While all centers use conventional PFT, MBW, and infant/preschool PFT are used in one-fifth and one-third of centers, respectively. While the majority of programs use TBBx, only 41.7% would obtain a diagnosis based on tissue histopathology over noninvasive techniques if CLAD is suspected. Utilization of biomarkers is still limited.

CONCLUSIONS

Our results indicate continued use of conventional PFT along with chest CT and less so CXR for CLAD detection and monitoring in the large majority of centers. Infant/preschool PFT and novel methods such as MBW are used in a few centers only. Respondents agreed there is a timely need for pediatric consensus guidelines on CLAD detection and monitoring.

Free-Breathing Low-Field MRI of the Lungs Detects Functional Alterations Associated With Persistent Symptoms After COVID-19 Infection

OBJECTIVES

With the COVID-19 pandemic, repetitive lung examinations have become necessary to follow-up symptoms and associated alterations. Low-field MRI, benefiting from reduced susceptibility effects, is a promising alternative for lung imaging to limit radiations absorbed by patients during CT examinations, which also have limited capability to assess functional alterations. The aim of this investigative study was to explore the functional abnormalities that free-breathing 0.55 T MRI in combination with the phase-resolved functional lung (PREFUL) analysis could identify in patients with persistent symptoms after COVID-19 infection.

MATERIALS AND METHODS

Seventy-four COVID-19 patients and 8 healthy volunteers were prospectively scanned in free-breathing with a balanced steady-state free-precession sequence optimized at 0.55 T, 5 months postinfection on average. Normalized perfusion (Q), fractional ventilation (FV), and flow-volume loop correlation (FVLc) maps were extracted with the PREFUL technique. Q, FV, and FVLc defects as well as defect overlaps between these metrics were quantified. Morphological turbo-spin-echo images were also acquired, and the extent of abnormalities was scored by a board-certified radiologist. To investigate the functional correlates of persistent symptoms, a recursive feature elimination algorithm was applied to find the most informative variables to detect the presence of persistent symptoms with a logistic regression model and a cross-validation strategy. All MRI metrics, sex, age, body mass index, and the presence of preexisting lung conditions were included.

RESULTS

The most informative variables to detect persistent symptoms were the percentage of concurrent Q and FVLc defects and of areas free of those defects. A detection accuracy of 71.4% was obtained with these 2 variables when fitting the model on the entire dataset. Although none of the single variables differed between patients with and without persistent symptoms ( P > 0.05), the combined score of these 2 variables did ( P < 0.02). This score also showed a consistent increase from healthy volunteers (7.7) to patients without persistent symptoms (8.2) and with persistent symptoms (8.6). The morphological abnormality score showed poor correlation with the functional parameters.

CONCLUSIONS

Functional pulmonary examinations using free-breathing 0.55 T MRI with PREFUL analysis revealed potential quantitative markers of impaired lung function in patients with persistent symptoms after COVID-19 infection, potentially complementing morphologic imaging. Future work is needed to explore the translational relevance and clinical implication of these findings.

Bronchiolitis obliterans syndrome after lung or haematopoietic stem cell transplantation: current management and future directions

Bronchiolitis obliterans syndrome (BOS) may develop after either lung or haematopoietic stem cell transplantation (HSCT), with similarities in histopathological features and clinical manifestations. However, there are differences in the contributory factors and clinical trajectories between the two conditions. BOS after HSCT occurs due to systemic graft-versus-host-disease (GVHD), whereas BOS after lung transplantation is limited to the lung allograft. BOS diagnosis after HSCT is more challenging, as the lung function decline may occur due to extrapulmonary GVHD, causing sclerosis or inflammation in the fascia or muscles of the respiratory girdle. Treatment is generally empirical with no established effective therapies. This review provides rare insights and commonalities of both conditions, that are not well elaborated elsewhere in contemporary literature, and highlights the importance of cross disciplinary learning from experts in other transplant modalities. Treatment algorithms for each condition are presented, based on the published literature and consensus clinical opinion. Immunosuppression should be optimised, and other conditions or contributory factors treated where possible. When initial treatment fails, the ultimate therapeutic option is lung transplantation (or re-transplantation in the case of BOS after lung transplantation) in carefully selected candidates. Novel therapies under investigation include aerosolised liposomal cyclosporine, Janus kinase inhibitors, antifibrotic therapies, and (in patients with BOS after lung transplantation) B-cell–directed therapies. Effective novel treatments that have a tangible impact on survival and thereby avoid the need for lung transplantation or re-transplantation are urgently required.

PREFUL MRI Depicts Dual Bronchodilator Changes in COPD: A Retrospective Analysis of a Randomized Controlled Trial

Purpose

To assess whether dynamic ventilation and perfusion (Q) biomarkers derived by phase-resolved functional lung (PREFUL) MRI can measure treatment response to 14-day therapy with indacaterol-glycopyrronium (IND-GLY) and correlate to clinical outcomes including lung function, symptoms, and cardiac function in patients with chronic obstructive pulmonary disease (COPD), as determined by spirometry, body plethysmography, cardiac MRI, and dyspnea score measurements.

Materials and Methods

The cardiac left ventricular function in COPD (CLAIM) study enrolled patients aged 40 years or older with COPD, stable cardiovascular function, and hyperinflation (residual volume > 135% predicted). Dynamic MRI data of these patients were retrospectively analyzed using the PREFUL technique to assess the effect of 14-day IND-GLY treatment versus placebo on regional measurements of ventilation dynamics. After manual segmentation of the lung parenchyma, flow-volume loops of each voxel were correlated to an individualized reference flow-volume loop, creating a two-dimensional flow-volume loop correlation map (FVL-CM) as a measure of ventilation dynamics. Ventilation-perfusion match (VQM) was evaluated in combination with perfusion and regional ventilation (VQM_RVent) and with perfusion and the FVL-CM measurement (VQM_CM). For image and statistical analysis, the lung parenchyma was segmented as a region of interest by manually delineating the lung boundary and excluding the large (central) vessels for each section. Differences in ventilation, perfusion, and VQM between IND-GLY and placebo were compared using analysis of variance, with study treatment, patient, and period included as factors.

Results

Fifty patients (mean age, 64.3 years ± 7.65 [SD]; 35 men) were included in this analysis. IND-GLY significantly increased mean correlation as measured with FVL-CM versus that of placebo (least squares [LS] means treatment difference: 0.05 [95% CI: 0.03, 0.07]; P < .0001). Compared with placebo, IND-GLY increased mean Q (LS means treatment difference: 9.27 mL/min/100 mL [95% CI: 0.05, 18.49]; P = .049) and improved both VQM_CM and VQM_RVent (LS means treatment difference: 0.06 [95% CI: 0.03, 0.08]; P < .0001 and 0.05 [95% CI: 0.02, 0.08]; P = .001, respectively).

Conclusion

Regional ventilation dynamics and VQM measured by PREFUL MRI show treatment response in COPD.

Supplemental material is available for this article.

Clinical trial registration no. NTR6831

Keywords: MRI, COPD, Perfusion, Ventilation, Lung, Pulmonary

Published under a CC BY 4.0 license

Abnormal dynamic ventilation function of COVID-19 survivors detected by pulmonary free-breathing proton MRI

Objectives

To visualize and quantitatively assess regional lung function of survivors of COVID-19 who were hospitalized using pulmonary free-breathing ¹H MRI.

Methods

A total of 12 healthy volunteers and 27 COVID-19 survivors (62.4 ± 8.1 days between infection and image acquisition) were recruited in this prospective study and performed chest ¹H MRI acquisitions with free tidal breathing. Then, conventional Fourier decomposition ventilation (FD-V) and global fractional ventilation (FV_Global) were analyzed. Besides, a modified PREFUL (mPREFUL) method was developed to adapt to COVID-19 survivors and generate dynamic ventilation maps and parameters. All the ventilation maps and parameters were analyzed using Student’s t-test. Pearson’s correlation and a Bland-Altman plot between FV_Global and mPREFUL were analyzed.

Results

There was no significant difference between COVID-19 and healthy groups regarding a static FD-V map (0.47 ± 0.12 vs 0.42 ± 0.08; p = .233). However, mPREFUL demonstrated lots of regional high ventilation areas (high ventilation percentage (HVP): 23.7% ± 10.6%) existed in survivors. This regional heterogeneity (i.e., HVP) in survivors was significantly higher than in healthy volunteers (p = .003). The survivors breathed deeper (flow-volume loop: 5375 ± 3978 vs 1688 ± 789; p = .005), and breathed more air in respiratory cycle (total amount: 62.6 ± 19.3 vs 37.3 ± 9.9; p < .001). Besides, mPREFUL showed both good Pearson’s correlation (r = 0.74; p < .001) and Bland-Altman consistency (mean bias = −0.01) with FV_Global.

Conclusions

Dynamic ventilation imaging using pulmonary free-breathing ¹H MRI found regional abnormity of dynamic ventilation function in COVID-19 survivors.

Key Points

• Pulmonary free-breathing¹H MRI was used to visualize and quantitatively assess regional lung ventilation function of COVID-19 survivors.

• Dynamic ventilation maps generated from¹H MRI were more sensitive to distinguish the COVID-19 and healthy groups (total air amount: 62.6 ± 19.3 vs 37.3 ± 9.9; p < .001), compared with static ventilation maps (FD-V value: 0.47 ± 0.12 vs 0.42 ± 0.08; p = .233).

• COVID-19 survivors had larger regional heterogeneity (high ventilation percentage: 23.7% ± 10.6% vs 13.1% ± 7.9%; p = .003), and breathed deeper (flow-volume loop: 5375 ± 3978 vs 1688 ± 789; p = .005) than healthy volunteers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-022-08605-w.

Novel biomarkers of chronic lung allograft dysfunction: is there anything reliable?

PURPOSE OF REVIEW

Chronic lung allograft dysfunction (CLAD) remains a major barrier preventing long-term survival following lung transplantation. As our clinical knowledge regarding its definition and presentation has significantly improved over the last years, adequate biomarkers to predict development of CLAD, phenotype of CLAD or prognosis post-CLAD diagnosis are definitely needed.

RECENT FINDINGS

Radiological and physiological markers are gradually entering routine clinical practice. In-depth investigation of biological samples including broncho-alveolar lavage, biopsy and serum has generated potential biomarkers involved in fibrogenesis, airway injury and inflammation but none of these are universally accepted or implemented although progress has been made, specifically regarding donor-derived cell-free DNA and donor-specific antibodies.

SUMMARY

Although a lot of promising biomarkers have been put forward, a very limited number has made it to routine clinical practice. Nevertheless, a biomarker that leads to earlier detection or more adequate disease phenotyping would advance the field enormously.

Quantitative Multivolume Proton-Magnetic Resonance Imaging in Lung Transplant Recipients: Comparison With Computed Tomography and Spirometry

RATIONALE AND OBJECTIVES

Acute and chronic graft rejection remains the major problem in clinical surveillance of lung-transplanted patients and early detection of complications is of capital importance to allow the optimal therapeutic option. The aim of this study was to investigate the role of quantitative non contrast-enhanced magnetic resonance imaging (MRI) as a non-ionizing imaging modality to assess ventilation impairment in patients who have undergone lung transplantation, in comparison with quantitative computed tomography (CT) and spirometry.

MATERIALS AND METHODS

Ten lung-transplanted patients (39 ±12 years, forced-expiratory volume in 1 second (FEV1) = 81 ± 27%, forced vital capacity (FVC) = 87 ± 27%) were acquired in breath-hold at full-expiration and full-inspiration with 1.5T MRI and CT. Maps of expiratory-inspiratory difference in MR signal-intensity and CT-density were computed to estimate regional ventilation. Based on expiratory, inspiratory, and expiratory-inspiratory difference values, each pixel was classified as healthy (H), low ventilation (LV), air trapping (AT), and consolidation (C) and the percent extent of each class was quantified.

RESULTS

Overall, expiratory-inspiratory difference in MR signal-intensity correlated to CT-density (r = 0.64, p < 0.0001) and to FEV1 (ρ = 0.71, p = 0.02). The linear correlation between MRI and CT functional maps considering all the four classes is r = 0.93 (p < 0.0001). MRI percent volumes of H, AT, and C correlated to FEV1 %pred, with the highest correlation reported for AT (ρ = -0.82).

CONCLUSION

Results demonstrated a good agreement between MRI and CT ventilation imaging and between the corresponding percent volumes of lung damage. Quantitative MRI may represent an accurate non-ionizing imaging technique for longitudinal monitoring of lung transplant recipients.

Repeatability of dynamic 3D phase-resolved functional lung (PREFUL) ventilation MR Imaging in patients with chronic obstructive pulmonary disease and healthy volunteers

BACKGROUND

A previous study has demonstrated the feasibility of 3D phase-resolved functional lung (PREFUL) MRI in healthy volunteers and patients with chronic pulmonary disease. Before clinical use, the repeatability of the ventilation parameters derived from 3D PREFUL MRI must be determined.

PURPOSE

To evaluate repeatability of 3D PREFUL and to compare with pulmonary functional lung testing (PFT).

STUDY TYPE

Prospective.

POPULATION

Fifty-three healthy subjects and 13 patients with chronic obstructive pulmonary disease (COPD).

FIELD STRENGTH/SEQUENCE

A prototype 3D stack-of-stars spoiled-gradient-echo sequence at 1.5 T.

ASSESSMENT

Study participants underwent repeated MRI examination (median time interval between scans COPD/healthy subjects [interquartile range]: 7/0 days [6-8/0-0 days]) and one PFT carried out at the time of the baseline MRI. For 3D PREFUL, regional ventilation (RVent) and flow-volume loops were computed and rated by cross-correlation (CC). Also, ventilation time-to-peak (VTTP) was computed. Ventilation defect percentage (VDP) maps were obtained for RVent and CC.

STATISTICAL TESTS

Repeatability of 3D PREFUL parameters was evaluated using Bland-Altman analysis, coefficient of variation (COV) and intraclass correlation coefficient (ICC). The relation between 3D PREFUL and PFT measures (forced expiratory volume in 1 second (FEV₁ ) and forced vital capacity (FVC) was assessed using the Pearson correlation coefficient (r).

RESULTS

In healthy subjects and COPD patients, no significant bias (all P range: 0.09-0.77) and a moderate to good repeatability of RVent, VTTP, and VDP_RVent were found (COV range: 0.1%-18.2%, ICC range: 0.51-0.88). For CC and VDP_CC moderate repeatability was found (COV range: 0.6%-43.6%, ICC: 0.38-0.60). CC, VDP_RVent , and VDP_CC showed a good correlation with FEV₁ (all |r| > 0.58, all P < 0.05) and FEV₁ /FVC ratio (all |r| > 0.62, all P < 0.05).

DATA CONCLUSION

3D PREFUL provided a good repeatability of RVent, VTTP, and VDP_RVent and moderate repeatability of CC and VDP_CC in healthy volunteers and COPD patients, and correlated well with FEV₁ and FEV₁ /FVC.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 2.

Chronic Lung Allograft Dysfunction: Review of CT and Pathologic Findings

Chronic lung allograft dysfunction (CLAD) is the most common cause of mortality in lung transplant recipients after the 1st year of transplantation. CLAD has traditionally been classified into two distinct obstructive and restrictive forms: bronchiolitis obliterans syndrome and restrictive allograft syndrome. However, CLAD may manifest with a spectrum of imaging and pathologic findings and a combination of obstructive and restrictive physiologic abnormalities. Although the initial CT manifestations of CLAD may be nonspecific, the progression of findings at follow-up should signal the possibility of CLAD and may be present on imaging studies prior to the development of functional abnormalities of the lung allograft. This review encompasses the evolution of CT findings in CLAD, with emphasis on the underlying pathogenesis and pathologic condition, to enhance understanding of imaging findings. The purpose of this article is to familiarize the radiologist with the initial and follow-up CT findings of the obstructive, restrictive, and mixed forms of CLAD, for which early diagnosis and treatment may result in improved survival. Supplemental material is available for this article. © RSNA, 2021.

Flow Volume Loop and Regional Ventilation Assessment Using Phase-Resolved Functional Lung (PREFUL) MRI: Comparison With 129 Xenon Ventilation MRI and Lung Function Testing

BACKGROUND

Regional flow volume loop ventilation-weighted noncontrast-enhanced proton lung MRI in free breathing has emerged as a novel technique for assessment of regional lung ventilation, but has yet not been validated with ¹²⁹ Xenon MRI (¹²⁹ Xe-MRI), a direct visualization of ventilation in healthy volunteers, cystic fibrosis (CF), and chronic obstructive pulmonary disease (COPD) patients.

PURPOSE

To compare regional ventilation and regional flow volume loops measured by noncontrast-enhanced ventilation-weighted phase-resolved functional lung MRI (PREFUL-MRI) with ¹²⁹ Xe-MRI ventilation imaging and with lung function test parameters.

STUDY TYPE

Retrospective study.

POPULATION

Twenty patients with COPD, eight patients with CF, and six healthy volunteers.

FIELD STRENGTH/SEQUENCE

PREFUL and ¹²⁹ Xe-MRI gradient echo sequences were acquired at 1.5T.

ASSESSMENT

Coronal slices of PREFUL-MRI (free breathing) and ¹²⁹ Xe-MRI (single breath-hold) were acquired on the same day, matched by their ventrodorsal position and coregistered for evaluation. Ventilation defect percentage (VDP) was calculated based on regional ventilation (RV), regional flow volume loops (RFVL), or ¹²⁹ Xe-MRI with two different threshold methods. A combined VDP was calculated for RV and RFVL. Additionally, lung function testing was performed (such as the forced expiratory volume in 1 second [FEV₁ ]) was used.

STATISTICAL TESTS

The obtained parameters were compared using Wilcoxon tests, correlated using Spearman's correlation coefficient (r), and agreement between PREFUL and ¹²⁹ Xe-MRI parameters was assessed using Bland-Altman analysis and Dice coefficients.

RESULTS

VDP measured by PREFUL and ¹²⁹ Xe were significantly correlated with both thresholding techniques (r = 0.62-0.69, P < 0.05 for all) and with lung function test parameters. Combined RV and RFVL PREFUL defect maps correlated with lung function testing (eg, with FEV₁ r = -0.87 P < 0.05), and showed better regional agreement to ¹²⁹ Xe-MRI ventilation defects (Dice coefficient defect 0.413) with significantly higher VDP values (10.2 ± 27.3, P = 0.04) than either PREFUL defect map alone.

DATA CONCLUSION

Combined RV and RFVL PREFUL defect maps likely increase sensitivity to mild airway obstruction with increased VDP values compared to ¹²⁹ Xe-MRI, and correlate strongly with lung function test parameters.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 2.

3D phase-resolved functional lung ventilation MR imaging in healthy volunteers and patients with chronic pulmonary disease

PURPOSE

To test the feasibility of 3D phase-resolved functional lung (PREFUL) MRI in healthy volunteers and patients with chronic pulmonary disease, to compare 3D to 2D PREFUL, and to investigate the required temporal resolution to obtain stable 3D PREFUL measurement.

METHODS

Sixteen participants underwent MRI using 2D and 3D PREFUL. Retrospectively, the spatial resolution of 3D PREFUL (4 × 4 × 4 mm³ ) was decreased to match the spatial resolution of 2D PREFUL (4 × 4 × 15 mm³ ), abbreviated as 3D_lowres . In addition to regional ventilation (RVent), flow-volume loops were computed and rated by a cross-correlation (CC). Ventilation defect percentage (VDP) maps were obtained. RVent, CC, VDP_RVent , and VDP_CC were compared for systematic differences between 2D, 3D_lowres , and 3D PREFUL. Dividing the 3D PREFUL data into 4- (≈ 20 phases), 8- (≈ 40 phases), and 12-min (≈ 60 phases) acquisition pieces, the ventilation parameter maps, including the heterogeneity of ventilation time to peak, were tested regarding the required temporal resolution.

RESULTS

RVent, CC, VDP_RVent , and VDP_CC  presented significant correlations between 2D and 3D PREFUL (r = 0.64-0.94). CC and VDP_CC  of 2D and 3D_lowres  PREFUL were significantly different (P < .0113). Comparing 3D_lowres  and 3D PREFUL, all parameters were found to be statistically different (P < .0045).

CONCLUSION

3D PREFUL MRI depicts the whole lung volume and breathing cycle with superior image resolution and with likely more precision compared to 2D PREFUL. Furthermore, 3D PREFUL is more sensitive to detect regions of hypoventilation and ventilation heterogeneity compared to 3D_lowres  PREFUL, which is important for early detection and improved monitoring of patients with chronic lung disease.

Noninvasive methods for detection of chronic lung allograft dysfunction in lung transplantation

Lung transplantation (LTx) is the only therapeutic option for end-stage lung diseases. Chronic lung allograft dysfunction (CLAD), which manifests as airflow restriction and/or obstruction, is the primary factor limiting the long-term survival of patients after surgery. According to histopathological and radiographic findings, CLAD comprises two phenotypes, bronchiolitis obliterans syndrome and restrictive allograft syndrome. Half of all lung recipients will develop CLAD in 5 years, and this rate may increase up to 75% 10 years after surgery owing to the paucity in accurate and effective early detection and treatment methods. Recently, many studies have presented noninvasive methods for detecting CLAD and improving diagnosis and intervention. However, the significance of accurately detecting CLAD remains controversial. We reviewed published studies that have presented noninvasive methods for detecting CLAD to highlight the current knowledge on clinical symptoms, spirometry, imaging examinations, and other methods to detect the disease.

Proton MRI of the Lung: How to Tame Scarce Protons and Fast Signal Decay

Pulmonary proton MRI techniques offer the unique possibility of assessing lung function and structure without the requirement for hyperpolarization or dedicated hardware, which is mandatory for multinuclear acquisition. Five popular approaches are presented and discussed in this review: 1) oxygen enhanced (OE)-MRI; 2) arterial spin labeling (ASL); 3) Fourier decomposition (FD) MRI and other related methods including self-gated noncontrast-enhanced functional lung (SENCEFUL) MR and phase-resolved functional lung (PREFUL) imaging; 4) dynamic contrast-enhanced (DCE) MRI; and 5) ultrashort TE (UTE) MRI. While DCE MRI is the most established and well-studied perfusion measurement, FD MRI offers a free-breathing test without any contrast agent and is predestined for application in patients with renal failure or with low compliance. Additionally, FD MRI and related methods like PREFUL and SENCEFUL can act as an ionizing radiation-free V/Q scan, since ventilation and perfusion information is acquired simultaneously during one scan. For OE-MRI, different concentrations of oxygen are applied via a facemask to assess the regional change in T₁ , which is caused by the paramagnetic property of oxygen. Since this change is governed by a combination of ventilation, diffusion, and perfusion, a compound functional measurement can be achieved with OE-MRI. The known problem of fast T₂ * decay of the lung parenchyma leading to a low signal-to-noise ratio is bypassed by the UTE acquisition strategy. Computed tomography (CT)-like images allow the assessment of lung structure with high spatial resolution without ionizing radiation. Despite these different branches of proton MRI, common trends are evident among pulmonary proton MRI: 1) free-breathing acquisition with self-gating; 2) application of UTE to preserve a stronger parenchymal signal; and 3) transition from 2D to 3D acquisition. On that note, there is a visible convergence of the different methods and it is not difficult to imagine that future methods will combine different aspects of the presented methods.

Imaging indications and findings in evaluation of lung transplant graft dysfunction and rejection

Lung transplantation is a treatment option in end-stage lung disease. Complications can develop along a continuum in the immediate or longer post-transplant period, including surgical and technical complications, primary graft dysfunction, rejection, infections, post-transplant lymphoproliferative disorder, and recurrence of the primary disease. These complications have overlapping clinical and imaging features and often co-exist. Time of onset after transplant is helpful in narrowing the differential diagnosis. In the early post transplantation period, imaging findings are non-specific and need to be interpreted in the context of the clinical picture and other investigations. In contrast, imaging plays a key role in diagnosing and monitoring patients with chronic lung allograft dysfunction. The goal of this article is to review primary graft dysfunction, acute rejection, and chronic rejection with emphasis on the role of imaging, pathology findings, and differential diagnosis.

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.