Effects of Anti-T2 Biologic Treatment on Lung Ventilation Evaluated by MRI in Adults With Prednisone-Dependent Asthma

Biologics and airway remodeling in asthma: early, late, and potential preventive effects

Although airway remodeling in severe and/or fatal asthma is still considered irreversible, its individual components as a cause of clinical symptoms and/or lung function changes remain largely unknown. While inhaled glucocorticoids have not consistently been shown to affect airway remodeling, biologics targeting specific pathways of airway inflammation have been shown to improve lung function, mucus plugging, and airway structural changes that can exceed those seen with glucocorticoids. This superiority of biologic treatment, which cannot be solely explained by insufficient doses or limited durations of glucocorticoid therapies, needs to be further explored. For this field of research, we propose a novel classification of the potential effects of biologics on airway remodeling into three temporal effects: early effects (days to weeks, primarily modulating inflammatory processes), late effects (months to years, predominantly affecting structural changes), and potential preventive effects (outcomes of early treatment with biologics). For the identification of potential preventive effects of biologics, we call for studies exploring the impact of early biological treatment on airway remodeling in patients with moderate-to-severe asthma, which should be accompanied by a long-term evaluation of clinical parameters, biomarkers, treatment burden, and socioeconomic implications.

New frontiers in asthma chest imaging

Modern pulmonary imaging can reveal underlying pathologic and pathophysiologic changes in the lungs of people with asthma, with important clinical implications. A multitude of imaging modalities, including computed tomography, magnetic resonance imaging, optical coherence tomography, and endobronchial ultrasound, are now being used to examine underlying structure-function relationships. Imaging-based biomarkers from these techniques, including airway dimensions, blood vessel volumes, mucus scores, extent of ventilation defect, and extent of air trapping, often have increased sensitivity compared with that of traditional lung function measurements and are increasingly being used as end points in clinical trials. Imaging has been crucial to recent improvements in our understanding of the relationships between type 2 inflammation, eosinophilia, and mucus extent. With the advent of effective anti-type 2 biologic therapies, computed tomography and magnetic resonance imaging techniques can identify not just which patients benefit from therapy but why they benefit. Clinical trials have begun to assess the utility of imaging to prospectively plan airway therapy targets in bronchial thermoplasty and have potential to direct future bronchoscopic therapies. Together, imaging techniques provide a diverse set of tools to investigate how spatially distributed airway, blood, and parenchymal abnormalities shape disease heterogeneity in patients with asthma.

Mucus Plug Score Predicts Clinical and Pulmonary Function Response to Biologic Therapy in Patients With Severe Asthma

BACKGROUND

Mucus plugging has been identified as an important feature of severe asthma contributing to airway obstruction and disease severity. Recently, improvement in mucus plugging has been found on treatment with several biologic therapies.

OBJECTIVES

To analyze associations of baseline characteristic with the mucus plugging score (MPS) and to determine whether the MPS at baseline predicts the clinical and functional response to biologic treatment in patients with severe asthma.

METHODS

We retrospectively analyzed biologic-naive patients with a suitable computed tomography scan available at baseline. We calculated the MPS and analyzed correlations with baseline parameters and improvements in biomarkers, pulmonary function, and clinical parameters after 4 months of biologic therapy.

RESULTS

We included 113 patients in the baseline cohort, 101 patients of whom had sufficient data after 4 months of biologic therapy for the follow-up analysis. Computed tomography showed mucus plugging in 77% of patients (median MPS, 4). Multivariate regression analysis showed a correlation of MPS with lower FEV1 (ρ = -0.24; P = .009) and diffusing capacity for carbon monoxide (ρ = -0.26; P = .01), and higher FeNO (ρ = .36; P = .0003) at baseline. Patients received treatment with anti-IgE (8.8%), anti-IL-5 (27.4%), anti-IL-5R (37.2%), anti-IL-4R (25.7%), and anti-thymic stromal lymphopoietin (0.9%) in clinical routine. Baseline MPS correlated with improvements in FEV1 (β = 0.72; P = .01) and Asthma Control Test (β = 0.24; P = .001) in multivariate regression analysis.

CONCLUSION

Our study suggests that a higher MPS correlates with worse pulmonary function at baseline but also predicts a larger clinical and pulmonary function response to biologic therapies in severe asthma.

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.

Ventilation Heterogeneity Is a Treatable Trait in Severe Asthma

BACKGROUND

Ventilation heterogeneity (VH) is a feature of asthma and indicates small airway disease. Nuclear imaging methods assess VH, which can facilitate clinical diagnosis and further our understanding of disease aetiology.

OBJECTIVE

We sought to assess VH in severe eosinophilic asthma (SEA) using ventilation/perfusion single-photon emission computed tomography (V/P SPECT), and to assess its use as an objective test of the effect of biologic treatment for ventilation defects in SEA.

METHODS

Adults (≥18 y) with severe asthma were recruited to participate in a cross-sectional observational study. Participants underwent a clinical assessment and V/P SPECT CT using Technegas as the ventilation agent. Measures were repeated for a nested before-after treatment study in people with SEA commencing biologics.

RESULTS

A total of 62 participants with severe asthma were recruited. From this, 38 participants with SEA were included in the before-after study. The VH was associated with clinical variables such as lung function impairment and significantly improved after monoclonal antibody treatment in the severe asthma group. The changes in VH correlated with change in post bronchodilator forced expiratory volume in 1 second (FEV1) %predicted (r = -0.503; P = .001) and post bronchodilator FEV1/FVC (forced vital capacity) (r = -0.415; P = .01).

CONCLUSIONS

The VH is clinically significant, measurable, and treatable, which establishes VH as a treatable trait in severe asthma.

Specific Ventilation in Severe Asthma Evaluated with Noncontrast Tidal Breathing 1H MRI

Purpose To determine if proton (1H) MRI-derived specific ventilation is responsive to bronchodilator (BD) therapy and associated with clinical biomarkers of type 2 airway inflammation and airways dysfunction in severe asthma. Materials and Methods In this prospective study, 27 participants with severe asthma (mean age, 52 years ± 9 [SD]; 17 female, 10 male) and seven healthy controls (mean age, 47 years ± 16; five female, two male), recruited between 2018 and 2021, underwent same-day spirometry, respiratory oscillometry, and tidal breathing 1H MRI. Participants with severe asthma underwent all assessments before and after BD therapy, and type 2 airway inflammatory biomarkers were determined (blood eosinophil count, sputum eosinophil percentage, sputum eosinophil-free granules, and fraction of exhaled nitric oxide) to generate a cumulative type 2 biomarker score. Specific ventilation was derived from tidal breathing 1H MRI and its response to BD therapy, and relationships with biomarkers of type 2 airway inflammation and airway dysfunction were evaluated. Results Mean MRI specific ventilation improved with BD inhalation (from 0.07 ± 0.04 to 0.11 ± 0.04, P < .001). Post-BD MRI specific ventilation (P = .046) and post-BD change in MRI specific ventilation (P = .006) were greater in participants with asthma with type 2 low biomarkers compared with participants with type 2 high biomarkers of airway inflammation. Post-BD change in MRI specific ventilation was correlated with change in forced expiratory volume in 1 second (r = 0.40, P = .04), resistance at 5 Hz (r = -0.50, P = .01), resistance at 19 Hz (r = -0.42, P = .01), reactance area (r = -0.54, P < .01), and reactance at 5 Hz (r = 0.48, P = .01). Conclusion Specific ventilation evaluated with tidal breathing 1H MRI was responsive to BD therapy and was associated with clinical biomarkers of airways disease in participants with severe asthma. Keywords: MRI, Severe Asthma, Ventilation, Type 2 Inflammation Supplemental material is available for this article. © RSNA, 2023 See also the commentary by Moore and Chandarana in this issue.

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.

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.

CT Mucus Score and 129Xe MRI Ventilation Defects After 2.5 Years' Anti-IL-5Rα in Eosinophilic Asthma

BACKGROUND

We previously showed in patients with poorly controlled eosinophilic asthma that a single dose of benralizumab resulted in significantly improved asthma-control-questionnaire (ACQ-6) score and ¹²⁹Xe MRI ventilation defect percent (VDP), 28 days post-injection, and ¹²⁹Xe MRI VDP and CT airway mucus occlusions were shown to independently predict this early ACQ-6 response to benralizumab.

RESEARCH QUESTION

Do early VDP responses at 28 days persist, and do FEV₁, fractional exhaled nitric oxide (Feno), and mucus plug score improve during a 2.5 year treatment period?

STUDY DESIGN AND METHODS

Participants with poorly controlled eosinophilic asthma completed spirometry, ACQ-6, and MRI, 28 days, 1, and 2.5 years after benralizumab; chest CT was acquired at enrollment and 2.5 years later.

RESULTS

Of 29 participants evaluated at 28 days post-benralizumab, 16 participants returned for follow-up while on therapy at 1 year, and 13 participants were evaluable while on therapy at 2.5 years, post-benralizumab initiation. As compared with 28 days post-benralizumab, ACQ-6 score (2.0 ± 1.4) significantly improved after 1 year (0.5 ± 0.6, P = .02; 95% CI, 0.1-1.1) and 2.5 years (0.5 ± 0.5, P = .03; 95% CI, 0.1-1.1). The mean VDP change at 2.5 years (-4% ± 3%) was greater than the minimal clinically important difference, but not significantly different from VDP measured 28 days post-benralizumab. Mucus score (3 ± 4) was significantly improved at 2.5 years (1 ± 1, P = .03; 95% CI, 0.3-5.5). In six of eight participants with previous occlusions, mucus plugs vanished or substantially diminished 2.5 years later. VDP (P < .001) and mucus score (P < .001) measured at baseline, but not Feno or FEV₁, independently predicted ACQ score after 2.5 years.

INTERPRETATION

In poorly controlled eosinophilic asthma, early MRI VDP responses at 28 days post-benralizumab persisted 2.5 years later, alongside significantly improved mucus score and asthma control.

The Pathology of Asthma: What Is Obstructing Our View?

Despite the advent of sophisticated and efficient new biologics to treat inflammation in asthma, the disease persists. Even following treatment, many patients still experience the well-known symptoms of wheezing, shortness of breath, and coughing. What are we missing? Here we examine the evidence that mucus plugs contribute to a substantial portion of disease, not only by physically obstructing the airways but also by perpetuating inflammation. In this way, mucus plugs may act as an immunogenic stimulus even in the absence of allergen or with the use of current therapeutics. The alterations of several parameters of mucus biology, driven by type 2 inflammation, result in sticky and tenacious sputum, which represents a potent threat, first due to the difficulties in expectoration and second by acting as a platform for viral, bacterial, or fungal colonization that allows exacerbations. Therefore, in this way, mucus plugs are an overlooked but critical feature of asthmatic airway disease.

Imaging Regional Airway Involvement of Asthma: Heterogeneity in Ventilation, Mucus Plugs and Remodeling

The imaging of asthma using chest computed tomography (CT) is well-established (Jarjour et al., Am J Respir Crit Care Med 185(4):356-62, 2012; Castro et al., J Allergy Clin Immunol 128:467-78, 2011). Moreover, recent advances in functional imaging of the lungs with advanced computer analysis of both CT and magnetic resonance images (MRI) of the lungs have begun to play a role in quantifying regional obstruction. Specifically, quantitative measurements of the airways for bronchial wall thickening, luminal narrowing and distortion, the amount of mucus plugging, parenchymal density, and ventilation defects that could contribute to the patient's disease course are instructive for the entire care team. In this chapter, we will review common imaging methods and findings that relate to the heterogeneity of asthma. This information can help to guide treatment decisions. We will discuss mucous plugging, quantitative assessment of bronchial wall thickening, delta lumen phenomenon, parenchymal low-density lung on CT, and ventilation defect percentage on MRI as metrics for assessing regional ventilatory dysfunction.

Overall Response to Anti-IL-5/Anti-IL5-Rα Treatment in Severe Asthma Does Not Depend on Initial Bronchodilator Responsiveness

BACKGROUND

Positive bronchodilator responsiveness (BDR) (change in forced expiratory volume in 1 second [ΔFEV₁] ≥ +200 mL and ≥ +12%) after inhalation of a short-acting beta-2 agonist has been an inclusion criterion in licensing trials of anti-interleukin 5/anti-interleukin 5 receptor alpha (anti-IL-5/anti-IL-5Rα) biologics in severe asthma. However, in clinical practice, patients with severe uncontrolled asthma frequently show a negative BDR.

OBJECTIVE

To investigate whether the response to anti-IL5/anti-IL5Rα therapies differs between patients with positive and negative BDR at baseline.

METHODS

Retrospective multicenter analysis of treatment outcomes in patients with severe asthma receiving anti-IL-5/anti-IL-5Rα stratified for baseline BDR.

RESULTS

Of 133 patients included, 37 had a positive and 96 had a negative BDR at baseline. Following anti-IL-5/anti-IL-5Rα treatment, FEV₁ improved significantly in both groups compared with baseline (P < .0001), with no significant difference between patients with positive and negative BDR (ΔFEV₁ +493 mL vs +306 mL; P = .06). Forced vital capacity (FVC) increased (ΔFVC: +85 mL vs +650 mL; P < .01) and residual volume (RV) decreased (ΔRV +113 mL vs -307 mL; P < .01) significantly in patients with negative BDR. Median annualized exacerbations (0 vs 0; P = .7), reduction of exacerbation rate (Δexacerbations 0 vs -2; P = .07), continuous oral corticosteroids (OCS) use (Δpatients on OCS -35% vs -39%; P = .99) and improvement of Asthma Control Test (ACT) score (ΔACT 6 vs 5; P = .7) were similar in both groups. Multivariate logistic regression analysis showed no significant correlations of positive versus negative BDR with response parameters.

CONCLUSIONS

Both groups improved following treatment with similar responses concerning reduction of OCS therapy, exacerbations, and improvement of symptom control. Pulmonary function also improved in both groups during anti-IL-5/anti-IL-5Rα treatment, with differences in response patterns noted.

Pulmonary MRI and Cluster Analysis Help Identify Novel Asthma Phenotypes

BACKGROUND

Outside eosinophilia, current clinical asthma phenotypes do not show strong relationships with disease pathogenesis or treatment responses. While chest x-ray computed tomography (CT) phenotypes have previously been explored, functional MRI measurements provide complementary phenotypic information.

PURPOSE

To derive novel data-driven asthma phenotypic clusters using functional MRI airway biomarkers that better describe airway pathologies in patients.

STUDY TYPE

Retrospective.

POPULATION

A total of 45 patients with asthma who underwent post-bronchodilator ¹²⁹ Xe MRI, volume-matched CT, spirometry and plethysmography within a 90-minute visit.

FIELD STRENGTH/SEQUENCE

Three-dimensional gradient-recalled echo ¹²⁹ Xe ventilation sequence at 3 T.

ASSESSMENT

We measured MRI ventilation defect percent (VDP), CT airway wall-area percent (WA%), wall-thickness (WT, WT* [*normalized for age/sex/height]), lumen-area (LA), lumen-diameter (D, D*) and total airway count (TAC). Univariate relationships were utilized to select variables for k-means cluster analysis and phenotypic subgroup generation. Spirometry and plethysmography measurements were compared across imaging-based clusters.

STATISTICAL TESTS

Spearman correlation (ρ), one-way analysis of variance (ANOVA) or Kruskal-Wallis tests with post hoc Bonferroni correction for multiple comparisons, significance level 0.05.

RESULTS

Based on limited common variance (Kaiser-Meyer-Olkin-measure = 0.44), four unique clusters were generated using MRI VDP, TAC, WT* and D* (52 ± 14 years, 27 female). Imaging measurements were significantly different across clusters as was the forced expiratory volume in 1-second (FEV₁ %_pred ), residual volume/total lung capacity and airways resistance. Asthma-control (P = 0.9), quality-of-life scores (P = 0.7) and the proportions of severe-asthma (P = 0.4) were not significantly different. Cluster1 (n = 15/8 female) reflected mildly abnormal CT airway measurements and FEV₁ with moderately abnormal VDP. Cluster2 (n = 12/12 female) reflected moderately abnormal TAC, WT and FEV₁ . In Cluster3 and Cluster4 (n = 14/6 female, n = 4/1 female, respectively), there was severely reduced TAC, D and FEV₁ , but Cluster4 also had significantly worse, severely abnormal VDP (7 ± 5% vs. 41 ± 12%).

DATA CONCLUSION

We generated four proof-of-concept MRI-derived clusters of asthma with distinct structure-function pathologies. Cluster analysis of asthma using ¹²⁹ Xe MRI in combination with CT biomarkers is feasible and may challenge currently used paradigms for asthma phenotyping and treatment decisions.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage.

[Markers of severity and predictors of response to treatment in severe asthma]

Asthma is a multifactorial disease with complex pathophysiology. Knowledge of its immunopathology and inflammatory mechanisms is progressing and has led to the development over recent years of increasingly targeted therapeutic strategies. The objective of this review is to pinpoint the different predictive markers of asthma severity and therapeutic response. Obesity, nasal polyposis, gastroesophageal reflux disease and intolerance to aspirin have all been considered as clinical markers associated with asthma severity, as have functional markers such as bronchial obstruction, low FEV1, small daily variations in FEV1, and high FeNO. While sinonasal polyposis and allergic comorbidities are associated with better response to omalizumab, nasal polyposis or long-term systemic steroid use are associated with better response to antibodies targeting the IL5 pathway. Elevated total IgE concentrations and eosinophil counts are classic biological markers regularly found in severe asthma. Blood eosinophils are predictive biomarkers of response to anti-IgE, anti-IL5, anti-IL5R and anti-IL4R biotherapies. Dupilumab is particularly effective in a subgroup of patients with marked type 2 inflammation (long-term systemic corticosteroid therapy, eosinophilia≥150/μl or FENO>20 ppb). Chest imaging may help to identify severe patients by seeking out bronchial wall thickening and bronchial dilation. Study of the patient's environment is crucial insofar as exposure to tobacco, dust mites and molds, as well as outdoor and indoor air pollutants (cleaning products), can trigger asthma exacerbation. Wider and more systematic use of markers of severity or response to treatment could foster increasingly targeted and tailored approaches to severe asthma.

Small Airways: The “Silent Zone” of 2021 GINA Report?

Asthma is a chronic disease, affecting approximately 350 million people worldwide. Inflammation and remodeling in asthma involve the large airways, and it is now widely accepted that the small airways (those with an internal diameter <2 mm) are involved in the pathogenesis of asthma and are the major determinant of airflow obstruction in this disease. From a clinical perspective, small airways dysfunction (SAD) is associated with more severe bronchial hyperresponsiveness, worse asthma control and more exacerbations. Unlike the GOLD guidelines which, in their definition, identify COPD as a disease of the small airways, the Global Initiative for Asthma (GINA) guidelines do not refer to the prevalence and role of SAD in asthmatic patients. This decision seems surprising, given the growing body of compelling evidence accumulating pointing out the high prevalence of SAD in asthmatic patients and the importance of SAD in poor asthma control. Furthermore, and remarkably, SAD appears to possess the characteristics of a treatable pulmonary trait, making it certainly appealing for asthma control optimization and exacerbation rate reduction. In this mini-review article, we address the most recent evidence on the role of SAD on asthma control and critically review the possible inclusion of SAD among treatable pulmonary traits in international guidelines on asthma.

Lung MRI with hyperpolarised gases: current & future clinical perspectives

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

Pulmonary functional MRI: Detecting the structure-function pathologies that drive asthma symptoms and quality of life

Pulmonary functional MRI (PfMRI) using inhaled hyperpolarized, radiation-free gases (such as ³ He and ¹²⁹ Xe) provides a way to directly visualize inhaled gas distribution and ventilation defects (or ventilation heterogeneity) in real time with high spatial (~mm³ ) resolution. Both gases enable quantitative measurement of terminal airway morphology, while ¹²⁹ Xe uniquely enables imaging the transfer of inhaled gas across the alveolar-capillary tissue barrier to the red blood cells. In patients with asthma, PfMRI abnormalities have been shown to reflect airway smooth muscle dysfunction, airway inflammation and remodelling, luminal occlusions and airway pruning. The method is rapid (8-15 s), cost-effective (~$300/scan) and very well tolerated in patients, even in those who are very young or very ill, because unlike computed tomography (CT), positron emission tomography and single-photon emission CT, there is no ionizing radiation and the examination takes only a few seconds. However, PfMRI is not without limitations, which include the requirement of complex image analysis, specialized equipment and additional training and quality control. We provide an overview of the three main applications of hyperpolarized noble gas MRI in asthma research including: (1) inhaled gas distribution or ventilation imaging, (2) alveolar microstructure and finally (3) gas transfer into the alveolar-capillary tissue space and from the tissue barrier into red blood cells in the pulmonary microvasculature. We highlight the evidence that supports a deeper understanding of the mechanisms of asthma worsening over time and the pathologies responsible for symptoms and disease control. We conclude with a summary of approaches that have the potential for integration into clinical workflows and that may be used to guide personalized treatment planning.

Bronchial thermoplasty guided by hyperpolarised gas magnetic resonance imaging in adults with severe asthma: a 1-year pilot randomised trial

Patient-specific localisation of ventilation defects using hyperpolarised gas magnetic resonance imaging (MRI) introduces the possibility of regionally targeted bronchial thermoplasty (BT) for the treatment of severe asthma. We aimed to demonstrate that BT guided by MRI to ventilation defects reduces the number of radiofrequency activations while resulting in improved asthma quality-of-life and control scores that are non-inferior to standard BT. In a 1-year pilot randomised controlled trial, 14 patients with severe asthma who were clinically eligible to receive BT underwent hyperpolarised gas MRI to characterise ventilation defects and were randomised to MRI-guided or standard BT. End-points were improved Asthma Quality of Life Questionnaire (AQLQ) and Asthma Control Questionnaire (ACQ) scores, the proportion of AQLQ and ACQ responders and the number of radiofrequency activations and bronchoscopy sessions. Participants who underwent MRI-guided BT received 53% fewer radiofrequency activations than those who had standard BT (p=0.003). At 12 months, the mean improvement from baseline was similar between the MRI-guided group (n=5) and the standard group (n=7) for AQLQ score (MRI-guided: 1.8, 95% CI 0.1-3.5, p=0.04; standard: 0.7, 95% CI -0.9-2.3, p=0.30) (p=0.25) and ACQ-5 score (MRI-guided: -1.4, 95% CI -2.6- -0.2, p=0.03; standard: -0.7, 95% CI -1.3-0.0, p=0.04) (p=0.17). A similar proportion of participants in both groups achieved a clinically relevant improvement in AQLQ score (MRI-guided: 80%; standard: 71%) and ACQ-5 score (MRI-guided: 80%; standard: 57%). Hyperpolarised gas MRI-guided BT reduced the number of radiofrequency activations, and resulted in asthma quality of life and control improvements at 12 months that were non-inferior to standard BT.

Small airway dysfunction and poor asthma control: a dangerous liaison

Asthma is a common chronic condition, affecting approximately 339 million people worldwide. The main goal of the current asthma treatment guidelines is to achieve clinical control, encompassing both the patient symptoms and limitations and the future risk of adverse asthma outcomes. Despite randomized controlled trials showing that asthma control is an achievable target, a substantial proportion of asthmatics remain poorly controlled in real life. The involvement of peripheral small airways has recently gained greater recognition in asthma, and many studies suggest that the persistent inflammation at these sites leads to small airway dysfunction (SAD), strongly contributing to a worse asthma control. Overall, the impulse oscillometry (IOS), introduced in the recent years, seems to be able to sensitively assess small airways, while conventional spirometry does not. Therefore, IOS may be of great help in characterizing SAD and guiding therapy choice. The aim of this article is to review the literature on SAD and its influence on asthma control, emphasizing the most recent evidence.

Imaging for precision medicine: can V-P SPECT measure mepolizumab response in asthma?

Monoclonal antibody therapies are effective for many but not all people with severe asthma. Precision medicine guides treatment selection using biomarkers to select patients most likely to respond according to their inflammatory endotypes. However, when assessing response to treatment, greater precision is required. We report a case series describing treatment response to mepolizumab in four severe asthma patients, assessed by traditional methods and with objective ventilation/perfusion single photon emission computed tomography (V-P SPECT). In this series, patients with severe asthma received mepolizumab treatment with clinical outcomes recorded at commencement and at approximately 16 weeks post-treatment initiation. V-P SPECT imaging was performed before and after treatment to determine ventilation heterogeneity and perfusion, and its ability to assess treatment responsiveness. V-P SPECT shows promise as an objective measure to assess lung ventilation and perfusion to observe and assess responsiveness to mepolizumab. With quantification, this measure may allow better precision in determining treatment improvements.

[Lung imaging in severe asthma]

INTRODUCTION

Asthma is a common disease whose diagnosis does not typically rely on the results of imaging. However, chest CT has gained a key place over the last decade to support the management of patients with difficult to treat and severe asthma.

STATE OF THE ART

Bronchial wall thickening and mild dilatation or narrowing of bronchial lumen are frequently observed on chest CT in people with asthma. Bronchial wall thickening is correlated to the degree of obstruction and to bronchial wall remodeling and inflammation. Diverse conditions which can mimic asthma should be recognized on CT, including endobronchial tumours, interstitial pneumonias, bronchiectasis and bronchiolitis. Ground-glass opacities and consolidation may be related to transient eosinophilic infiltrates, infection or an associated disease (vasculitis, chronic eosinophilic pneumonia). Hyperdense mucous plugging is highly specific for allergic bronchopulmonary aspergillosis.

PERSPECTIVES

Airway morphometry, air trapping and quantitative analysis of ventilatory defects, with CT or MRI, can help to identify different morphological subgroups of patients with different functional or inflammatory characteristics. These imaging tools could emerge as new biomarkers for the evaluation of treatment response.

CONCLUSION

Chest CT is indicated in people with severe asthma to search for additional or alternative diagnoses. Quantitative imaging may contribute to phenotyping this patient group.