Demonstration of the heterogeneous distribution of asthma in the lungs using CT and hyperpolarized helium‐3 MRI

Abstract

Asthma is a chronic inflammatory disease that affects both the large and small airways and results in bronchoconstriction, mucous hypersecretion, smooth muscle hypertrophy, and subepithelial fibrosis. To gain insight into the pathophysiology of asthma, chest computed tomography (CT) has been investigated as a noninvasive method to evaluate airway wall thickness of medium and large airways. Hyperpolarized gas MRI can assess the functional alterations of airflow within the lung resulting from the structural changes in the airways. In this article, we review the application of CT-based techniques and hyperpolarized gas MRI to study structural and functional changes in asthma. From the result of studies with CT and hyperpolarized gas MRI, it is becoming apparent that asthma has a regional distribution within the lung, that is, some areas of the lung are more affected than others. Furthermore, there appears to be some persistence to this distribution which may explain the observed patterns of airway remodeling and provide targets for localized therapies such as local application of anti-inflammatory agents or bronchial thermoplasty. Thus, cross sectional imaging in asthma is providing new insights into the pathophysiology of the disease and has the potential to become essential in the guidance of localized treatments.

Distribution of airway smooth muscle remodelling in asthma: Relation to airway inflammation

“…The detection of airway remodelling (increased wall area and reduced luminal area) has been shown in asthma by using CT and MRI. 7,10,11 These studies, however, while showing evidence of regional remodelling are limited as they cannot determine structural differences that are present (e.g. increased ASM, mucous glands or reticular basement membrane thickness) and have difficulty measuring images beyond the 5th or 6th generation of airways.…”

“…While the aetiology of ventilation abnormalities is not fully understood, it is suspected to be the result of regional airway narrowing which may be due to local airway remodelling. 11 Very little is known about the variability of distribution of ASM remodelling within and between asthma cases. The aim of the present study was to examine the distribution (large and/or small airways) and type (hyperplasia and/or hypertrophy) of ASM remodelling within the bronchial tree.…”

Remodeling in asthma

“…Noninvasive imaging techniques used for this purpose include computed tomography (CT), magnetic resonance imaging, 197 and optical coherence tomography. 198 Of these methods, CT is the most well characterized.…”

Regional Ventilation Changes in the Lung: Treatment Response Mapping by Using Hyperpolarized Gas MR Imaging as a Quantitative Biomarker

“…Functional lung imaging with hyperpolarized gas magnetic resonance (MR) imaging provides three-dimensional (3D) images of lung ventilation in a short breath hold. Hyperpolarized helium 3 ( 3 He) MR imaging has been shown to be a sensitive measure of ventilation heterogeneity in asthma (7,8). Although numerous metrics have been derived to describe ventilation heterogeneity from both hyperpolarized xenon 129 ( 129 Xe) and 3 He images by using texture-based methods like feature analysis or clustering methods such as k-means clustering (9)(10)(11)(12), efforts have been focused on cross-sectional assessment of cohorts.…”