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

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.